LMLechko

Chapter 17, part 2
The Special Senses
Fibrous tunic
Defined as the outermost layer of the eye
Provides mechanical support and protection
Serves as an attachment site for the extrinstic muscles of the eyes
Contain aids for focusing

Outer surface
Large part of the outer surface is called the sclera of the white of the eye
Composed of dense connective tissue containing collage and elastic fibers
Thickest over the posterior surface of the eye and thinnest on the anterior surface of the eye near the optic nerve
Six extrinsic eye muscles insert on the sclera of the eye


Sclera composition
Small blood vessels and nerves that penetrate into the internal structures of the eye
The cornea is continuous with the sclera and the border between the sclera and the cornea is called the limbus

Cornea composition
No blood vessels
Nutrients and oxygen are obtained from tears
Also has many free nerve endings
Vascular tunic
Composition:
Blood vessels
Lymph vessels
Intristic eye muscles

Function:
Provides a route for blood and lymph vessels
Regulates the amount of light that enters the eye
Secreting and reabsorbing the aqueous humor
Control the shape of the lens

More on composition
Iris
Ciliary body
choroid
Iris
Contains
Blood vessels
Pigment cells
Two layers of smooth muscle tissue which regulate the diameter of the pupil, these sphincter muscles are under autonomic control
Pupillary constrictor muscles
Pupillary dilator muscles

The body of the iris
High vascularized pigmented loose connective tissue
The anterior portion contains the melanocytes which are responsible for the color on the surface of the eye
Ciliary Body
The iris is anchored to the ciliary body at its periphery
This ciliary body begins at the junction of the cornea and the sclera and ends at the orta serrata
The bulk of this ciliary body consists of ciliary muscle
Suspensory ligaments attach to the ciliary processes


Choroid
Has an extensive capillary network that delivers oxygen to the retina

Neutral Tunic
Also called the retina
Inner most portion of the eye

Composition
Outer most layer called the pigment part
Inner most layer called the neural part
Job functions
Pigment part absorbs the light the passes through the neutral part and prevents light from bouncing back to the neural part
The neural part contains blood vessels and processes preliminary visual information
Extent of the layers
Pigment part extends over the ciliary body and iris
The neural part extend just to the orta serrata

Retina: organization: the photoreceptors
Retina contains rods and cones
Cones densely packed at fovea (center of the macula lutea)
Retinal pathway
Rods and cones synapse with 6 million bipolar neurons which pass on information to ganglion cells, to the brain via the optic nerve
Axons of ganglion cells converge at blind spot (optic disc)
Horizontal cells and amacrine cells modify the signal passed along the retinal neurons by facilitation or inhibition
What are the jobs of the rods and cones?
The rods do not discriminate colors of light
The cones provides us with color vision
Three cone types determine the color you see
Also give us sharper clear images
However, they require more intense light to be active

Rod and cone distribution
125 million rods are found along the periphery of the retina
6 million cones span the posterior surface
Most found near the macula lutea
This region contain NO rods!
The highest concentration of the cones occurs at the center of the muscula lutea and this region is called the fovea
Region of sharpest vision
Optic disc
The axons from 1 million ganglion cells converge on the optic disc
This disc is the origin of cranial nerve II which proceeds to the diencephalon
The central retinal artery and vein can be found here
The optic disc has no photoreceptors
This area of contact is called the blind spot

Chamber of the eye
Anterior cavity
Anterior chamber
Posterior chamber
Posterior chamber

Aqueous humor
A fluid which circulates within the anterior cavity passing from the posterior chamber to the anterior chamber through the pupil
Formed by cells of the ciliary processes
Similar to CSF
This creates intraocular pressure which forces the neural layer against the pigmented layer
Returns from the posterior chamber back to the anterior chamber by passing through the canal of Schlemm
This is then passed onto the veins of the sclera


Viterous Body
Posterior portion of the eye contains the viterous body
Gelatin like in structure
Stabilizes the shape of the eye
Additional physical support to the retina
Fluid is made up of collagen and proteoglycans (these resemble cellulose like materials)
Never replaced
Figure 17.6 The Organization of the Retina
Eye anatomy: pause and review
Ciliary body and lens divide the anterior cavity of the eye into posterior (vitreous) cavity and anterior cavity
Anterior cavity further divided
anterior chamber in front of eye
posterior chamber between the iris and the lens
Figure 17.8 The Circulation of Aqueous Humor
Fluids in the eye
Aqueous humor circulates within the eye
diffuses through the walls of anterior chamber
passes through canal of Schlemm
re-enters circulation
Vitreous humor fills the posterior cavity.
Not recycled – permanent fluid
Lens
Posterior to the cornea and forms anterior boundary of posterior cavity
Posterior cavity contains vitreous humor
Lens helps focus
Light is refracted as it passes through lens
Accommodation is the process by which the lens adjusts to focus images
Normal visual acuity is 20/20
Figure 17.9 Image Formation
Figure 17.10 Accommodation
Figure 17.11 Visual Abnormalities
Visual physiology
Rods – respond to almost any photon
Cones – specific ranges of specificity
Figure 17.13 Rods and Cones
Photoreceptor structure
Outer segment with membranous discs
Narrow stalk connecting outer segment to inner segment
Light absorption occurs in the visual pigments
Derivatives of rhodopsin
Figure 17.14 Photoreception
Figure 17.14 Photoreception
Figure 17.15 Bleaching and Regeneration of Visual Pigments
Color sensitivity
Integration of information from red, blue and green cones
Colorblindness is the inability to detect certain colors
retinal adaptation
Dark adapted – most visual pigments are fully receptive to stimulation
Light adapted – pupil constricts and pigments bleached.
the visual pathway
Large M-cells monitor rods
Smaller more numerous P cells monitor cones
Figure 17.18 Convergence and Ganglion Cell Function
Seeing in stereo
Vision from the field of view transfers from one side to the other while in transit
Depth perception is obtained by comparing relative positions of objects from the two eyes
Figure 17.19 The Visual Pathways
Visual circadian rhythm
Input to suprachiasmic nucleus affects the function of the brainstem
Circadian rhythm ties to day-night cycle, and affects metabolic rates

Chapter 17, part 1
The Special Senses
Learning Objectives
Describe the sensory organs of smell, and trace the olfactory pathways to their destination in the brain.
Identify the accessory and internal structures of the eye, and explain their function.
Explain how light stimulates the production of nerve impulses, and trace the visual pathways to their destination in the brain.
Describe the structures of the external and middle ear and explain how they function.
Learning Objectives
Describe the parts of the inner ear and their roles in equilibrium and hearing.
Trace the pathways for the sensations of equilibrium and hearing to their destinations in the brain.
SECTION 17-1 Olfaction
What is the composition
The sense of smell as defined as the process called olfaction
These organs are located in the nasal cavity on either side of the nasal septum
Composition
Two layers
Olfactory epithelium
Here are located the olfactory receptors
Basal cells
Stem cells or supporting cells

Where is this epithelium found?
Inferior surface of the cribriform plate
Superior portion of the perpendicular plate
Superior nasal conchae
Underlying portions contain the olfactory glands
Olfactory receptors
They are considered to be highly modified neurons
The exposed tip of the neuron forms a bulb which extends beyond the surface of the epithelium and extends into the mucus
Here the cilia are found and have exposed surfaces for picking up chemicals

Where does olfaction occur?
Occurs on the surface of the cilia
There are special receptors called odorant binding proteins
The chemicals which bring about the response are called an ordorant
Ordorants trigger a chemical response through secondary messengers

Olfactory pathways
It is believed that as few as four molecules can trigger an response
Not all information will reach the olfactory centers
There is significant olfactory central adaptation
There is two or more axons which bundle themselves together after they emerge from the cribiform plate and pass the cerebrum
They also reach the hypothalamus and limbic system
The olfactory information that is collected, does not synapse in the thalamus before it goes to the cerebrum
Olfactory Discrimination
2000 – 400 smells
All olfactory cells look the same
50 primary smells
Pattern of receptor activity are interpreted determine the "smell"
Pattern determination fails with age
Olfactory organs: Review
Contain olfactory epithelium with olfactory receptors, supporting cells, basal cells
Olfactory receptors are modified neurons
Surfaces are coated with secretions from olfactory glands
Olfactory reception involved detecting dissolved chemicals as they interact with odorant binding proteins
Figure 17.1 The Olfactory Organs
Olfaction
Olfactory pathways
No synapse in the thalamus for arriving information
Olfactory discrimination
Can distinguish thousands of chemical stimuli
CNS interprets smells by pattern of receptor activity
Olfactory receptor population shows considerable turnover
Number of receptors declines with age
SECTION 17-2 Gustation
The beginning: where do we find
Taste receptors are distributed over the surface of the tongue and the adjacent portions of the pharynx and the larynx
The most important ones are found on the tongue
Adults have 3000 taste buds
Where find on the tongue? Found everywhere on tongue?
Three types of lingual papillae
Filiform
Fungiform
Circumvallate

Filiform
No taste receptors found here
These provide friction to help move food along

Fungiform
Contains 5 taste buds

Cicumvallate
Largest of the papillae
Contains about 100 taste buds
Form a V with the posterior margin of the tongue

How are taste buds put together?
They are placed in recessed spaces to isolate them from the rest of contents of the rest of the mouth
There are four different cell types within a taste bud
Stage one are the basal cells for repair and replacement
Stage four are the gustratory cells which are responsible for the taste
Each taste bud has a pore for fluids to enter
Gustatory cells last only 10 days
Taste receptors Quick review
Clustered in taste buds
Associated with lingual and circumvallate papillae
Contain basal cells which appear to be stem cells
Gustatory cells extend taste hairs or cilia through a narrow taste pore
Figure 17.2 Gustatory Reception

Gustatory pathways
Taste buds are monitored by cranial nerves VII, IX, and X
Synapse within the solitary nucleus of the medulla oblongata and the medial lemniscus
There the neurons axons that carry somatic sensory information on touch, pressure, and proprioception
Then on to the thalamus and finally the primary sensory cortex
When is there a conception perception?
That of taste is produced as the information received is correlated with other sensory data
This includes information about texture of the food
Other data is carried by the V cranial nerve
Sensitive to taste is enhanced by olfaction

Gustatory discrimination
Primary taste sensations are defined as being:
Sweet, sour, salty, bitter
Receptors also exist for umami and water
Taste sensitivity shows significant individual differences, some of which are inherited
The number of taste buds declines with age
What is umani?
Pleasant taste depending on the presence of amino acids
They are found in the circumvalatte papillae

Water receptors?
Found in the pharynx
Processed in the hypothalamus
It is known that it affects the production of ADH

What is the mechanism of gustatory?
Dissolved chemicals must come in contact with receptors
Different receptors for different tastes
The net is always a stimulation of sensory neurons from the taste receptors that produce an graded potential
Taste receptors adapt slowly but there is central adaptation reduces your sensitivity to a new taste presented

How do we define this threshold?
Two conditions
For unpleasant taste, the receptors respond more quickly
Sour tastes respond quickly
Sweet of salty is responding slower
But more sensitive to bitter, quinine compds

SECTION 17-3 Vision
Accessory structures of the eye; the divisions
Job function:
protection, lubrication, and support
Eyelids (palpebrae) separated by the palpebral fissure
Eyelashes
Tarsal glands
Lacrimal apparatus
The eyelids
Also called the palprebra
Keeps the surface of the eye lubricated and free from dust and debris
Capable of tight closure
The palprebra fissure separates the upper and lower eyelids
The eyelids are connected at the median and lateral canthus

Eyelashes
The eyelashes prevent foreign matter from reaching the eye
Did you know that there are small mites growing on your eyelids
Think of the contain of eyelash liner as a growth chamber for these bugs

Eyelashes and lubrication
We find that along the inner margin of the lid is a gland called the tarsal gland
The oil prevents the lids from sticking together
There are also lacrimal glands that produce secretions that are gritty
All glands subject to infection

Function of Lubrication
Keeps the conjunctival surface clean and moist
Tears reduce friction and prevent bacterial infections
Provide nutrients and oxygen portions to the conjunctival epithelium

Lacrimal appratus construction
Lacrimal glands and associated ducts
Lacrimalcanaliculi
Lacrimal sac
Nasolacrimal duct
How are demands meet?
Nutrient and oxygen demands are met by diffusion from the lacrimal secretions
Lacrimal apparatus: function
Secretions from the lacrimal gland contain lysozyme
Provides the key incredients and most of the volume of the tears that bathe the conjunctival surface
Tears form in the lacrimal glands, wash across the eye and collect in the lacrimal lake
Then pass through the lacrimal punctae, lacrimal canaliculi, lacrimal sac and nasolacrimal duct when these secretions drain from the eye itself
What is produced?
About 1 mL of tears/day
These secretions then mix with oils from accessory glands and form and oil slick that assists in lubrication and the slowly of evaporation
What does blinking do?
Blinking provides a sweeping action across the surface of the eye
Figure 17.3 Eternal Features and Accessory Structures of the Eye
external structures of the eye
Conjunctiva covers most of inner portion of the eyelids and the outer surface of the eye
This is really a mucus membrane made of two parts:
Palpebral conjunctiva
Ocular conjunctive
What is the cornea?
Cornea is transparent anterior portion in which light passes through
The occur conjunctiva ends here
This is covered by corneal epithelium
What is conjunctivitis?
Pink eye
Damage to the conjunctival surface
Characterized by dilation of blood vessels deep to the conjunctival eipthelium
The eye
Three layers
Outer fibrous tunic
Sclera, cornea, limbus
Middle vascular tunic
Iris, ciliary body, choroid
Inner nervous tunic
Retina
Figure 17.4 The Sectional Anatomy of the Eye
Structures
Posterior cavity
Viterous humor
Contains the retinal
Anterior cavity
Aqueous humor
Orbial fat
internal structures of the eye
Ciliary body
Ciliary muscles and ciliary processes, which attach to suspensory ligaments of lens
Retina
Outer pigmented portion
Inner neural part
Rods and cones
Figure 17.4 The Sectional Anatomy of the Eye
Figure 17.5 The Pupillary Muscles

SECTION 16-3 The Parasympathetic Division
Parasympathetic division:
Preganglionic neurons in the brainstem and sacral segments of spinal cord
Ganglionic neurons in peripheral ganglia located within or near target organs
Figure 16.7 The Organization of the Parasympathetic Division of the ANS
Organization and anatomy of the parasympathetic division
Preganglionic fibers leave the brain as cranial nerves III, VI, IX, X
Sacral neurons form the pelvic nerves
Figure 16.8 The Distribution of Parasympathetic Innervation
Parasympathetic activation
Effects produced by the parasympathetic division
relaxation
food processing
energy absorption
Neurotransmitters and parasympathetic functions
All parasympathetic fibers release ACh
Short-lived response as ACH is broken down by AChE and tissue cholinesterase
Postsynaptic membranes have two kinds of receptors
Muscarinic
Ach receptors respond to the poison
Nicotinic
Ach receptors which respond to nicotine
SECTION 16-4 Interactions Between the Sympathetic and Parasympathetic Divisions
Sympathetic and parasympathetic divisions
Sympathetic
Widespread influence on visceral and somatic structures
Parasympathetic
Innervates only visceral structures serviced by cranial nerves or lying within the abdominopelvic cavity
Dual innervation = organs that receive input from both systems
Summary: parasympathetic division
Parasympathetic division includes cranial nerves III, VII, IX, and X and sacral segments S2 – S4
Ganglion are located near target organs
Divisions are cholinergic
Effects are brief and site restricted

Anatomy of dual message delivery
Sympathetic and parasympathetic systems intermingle to form autonomic plexuses
Cardiac plexus
Pulmonary plexus
Esophageal plexus
Celiac plexus
Inferior mesenteric plexus
Hypogastric plexus
Figure 16.9 The Autonomic Plexuses
Comparison of the two divisions
Important physiological and functional differences exist
Figure 16.10 Summary: The Anatomical Differences between the Sympathetic and Parasympathetic Divisions
SECTION 16-5 Integration and Control of Autonomic Functions
Visceral reflexes
Visceral reflex arcs are the simplest function of the ANS
Long reflexes (interneurons)
Short reflexes (bypassing CNS)
Parasympathetic reflexes govern respiration, cardiovascular function and other visceral activities
Figure 16.11 Visceral Reflexes
Higher levels of autonomic control
Activity in the ANS is controlled by centers in the brainstem that deal with visceral functioning
Figure 16.12 Levels of Autonomic Control
SNS and ANS organized in parallel
Integration occurs at the brainstem and higher centers
Figure 16.13 A Comparison of Somatic and Autonomic Function
SECTION 16-6 High Order Functions
Higher order functions
Are performed by the cerebral cortex and involve complex interactions
Involve conscious and unconscious information processing
Are subject to modification and adjustment over time
Memory
Short term or long term
Memory consolidation is moving from short term to long term
Amnesia is the loss of memory due to disease or trauma
Figure 16.14 Memory Storage
Consciousness
Deep sleep, the body relaxes and cerebral cortex activity is low
REM sleep active dreaming occurs
The reticular activating system (RAS) is important to arousal and maintenance of consciousness
Figure 16.16 The Reticular Activating System
SECTION 16-7 Brain Chemistry and Behavior
Neurotransmitters and the brain
Neurotransmitters and brain function
Changes in balance between neurotransmitters can profoundly alter brain function
Personality and self-awareness
Characteristics of the brain as an integrated system rather than one specific component
SECTION 16-8 Aging and the Nervous System
Age-related changes
Reduction in brain size and weight
Reduction in the number of neurons
Decrease in blood flow to the brain
Changes in synaptic organization of the brain
Intracellular and extracellular changes in CNS neurons
You should now be familiar with:
The organization of the autonomic nervous system.
The structures and functions of the sympathetic and parasympathetic divisions of the ANS.
The mechanisms of neurotransmitter release in the sympathetic and parasympathetic divisions.
The effects of sympathetic and parasympathetic neurotransmitters on target organs and tissues.
The hierarchy of interacting levels of control in the ANS.
How memories are created, stored and recalled.
The effects of aging on the nervous system.

Learning Objectives
Compare the organization of the autonomic nervous system with the somatic nervous system.
Describe the structures and functions of the sympathetic and parasympathetic divisions of the ANS.
Describe the mechanisms of neurotransmitter release in the sympathetic and parasympathetic divisions.
Describe the effects of sympathetic and parasympathetic neurotransmitters on target organs and tissues.
Learning Objectives
Describe the hierarchy of interacting levels of control in the ANS
Explain how memories are created, stored and recalled.
Summarize the effects of aging on the nervous system.
SECTION 16-1 An Overview of the ANS
General information
Neural Integration II: The Autonomic Nervous System and Higher Order Functions
There are going to be two major goals here, compare:
The neural interactions that direct motor output
The subdivisions of the ANS based on structural and functional patters

Common ground
Both the somatic and autonomic nervous systems are efferent that carry motor commands to the skeletal system
In the somatic nervous system the commands form the CNS exert direct control over the the skeletal muscle
In the ANS motor neurons of the CNS synapse on visceral motor neurons in autonomic ganglion and it is through the ganglion that control is exerted

More
The visceral motor neurons of the CNS are known as preganglionic neurons and the axons are called prehanglionic fibers
Those that leave the ganglion are called postganglionic fibers


Somatic or visceral information input
Input can trigger visceral reflexes and these motor commands are distributed by the ANS
ANS (review)
Coordinates cardiovascular, respiratory, digestive, urinary and reproductive functions
Preganglionic neurons in the CNS send axons to synapse on ganglionic neurons in autonomic ganglia outside the CNS
Divisions of the ANS
Most often the divisions have opposing effects
However, some divisions are only controlled by one of the divisions
Sympathetic division (thoracolumbar, "fight or flight")
Thoracic and lumbar segments
Parasympathetic division (craniosacral, "rest and repose")
Preganglionic fibers leaving the brain and sacral segments
A general statement
The parasympathetic nervous system dominates under resting conditions
And the sympathetic nervous system kicks in under times of stress

Eneteric nervous system
Generally local control over digestive properties
But the activity can also be influenced by both the sympathetic and parasympathetic divisions
SECTION 16-2 The Sympathetic Division
Sympathetic division anatomy
Preganglionic neurons between segments T1 and L2
Ganglionic neurons in ganglia near vertebral column
The preganlionic fibers are short and the postganglionic fibers are long
The job is to prepare the body for fight of flight responses
Specialized neurons in adrenal glands
Parasympathetic division
The preganlionic fibers originate in the brain stem and the sacral segments of the spinal cord
They synapse in ganglion which are close to the target organ
This means that the preganlionic fibers are long and the postganglionic fibers are short
Job is to conserve energy
This means that if you consume a heavy meals, the activity is for digestions, absorption, and waste removal
Figure 16.3 The Organization of the Sympathetic Division of the ANS
Sympathetic division
The division consists of preganglionic neurons that are located between segments T1 and L2 of the spinal cord
The cell bodies are located in the gray matter of the lateral gray horns of their axons axons enter the ventral root at three segments

Sympathetic chain ganglion
Can also be called paaravertebral ganglion or lateral ganglion
These are found on both sides of the vertebral column
Innervates body wall, inside the thoracic cavity, and head and limbs

Collateral ganglia
Prevertebral ganglia
Innervates tissues and organs in the abdominopelvic cavity


Adrenal medullae
The center of each adrenal gland
Neurotransmitters released directly into the blood stream
Figure 16.4 Sympathetic Pathways
Figure 16.4 Sympathetic Pathways
Figure 16.4 Sympathetic Pathways
Sympathetic chain ganglion
Preganglionic fibers that carry motor commands that target structures in the body wall, thoracic cavity, or in the head, neck, or limbs, it will synapse in one or more sympathetic chain ganglion
Postganglionic fibers paths will differ
Postganglionic fibers
These control effectors in the body wall, head, neck, limbs

Organization and anatomy of the sympathetic division
The T1 and L2 spinal segments contain sympathetic preganglionic fibers
These segments of T1-L2, ventral roots give rise to myelinated white ramus
Which then lead to sympathetic chain ganglia or in the adrenal medulla
Sympathetic chain ganglia
Two final routes
Postganglionic fibers which control visceral effectors in wall, head, neck, or limbs
Potganglionic fibers which innervate structures of the heart and lungs form sympathetic nerves


Summary
The cervical, inferior lumbar, and sacral chain receive preganglionic innervation by preganglionic fibers from spinal segments T1 – L2 and every spinal nerve receives a gray ramus from a ganglionic of the sympathetic chain
Only the thoracic and superior lumbar ganglion T1 – L2 receive preganglionic fibers from white rami
Every spibal nerve receives gray ramus from a ganglion of the sympathetic chain
Collateral Ganglia
Figure 16.5 The Distribution of Sympathetic Innervation
Postganglionic fibers
Rejoin spinal nerves and reach their destination by way of the dorsal and ventral rami
Those targeting structures in the thoracic cavity form sympathetic nerves
Go directly to their destination
Abdominopelvic viscera
Sympathetic innervation via preganglionic fibers synapse within collateral ganglia
Splanchic nerves
Abdominopelvic viscera
Celiac ganglion
Innervates stomach, liver, gall bladder, pancreas, spleen
Superior mesenteric ganglion
Innervates small intestine and initial portion of large intestine
Inferior mesenteric ganglion
Innervates kidney, urinary bladder, sex organs, and final portion of large intestine
Sympathetic activation
In crises, the entire sympathetic division responds
Sympathetic activation
Affects include increased alertness, energy and euphoria, increased cardiovascular and respiratory activities, elevation in muscle tone, mobilization of energy resources
Neurotransmitters and sympathetic function
Stimulation of sympathetic division has two distinct results
Release of ACh or NE at specific locations
Secretion of E and NE into general circulation
Most postganglionic fibers are adrenergic, a few are cholinergic or nitroxidergic
Two types of receptors are alpha receptors and beta receptors
Sympathetic ganglionic neurons end in telodendria studded with varicosities filled with neurotransmitter
Adrenal Medullae
Preganglionic fibers enter an adrenal gland and proceed to its center, which is called adrenal medulla
This is a sympathetic ganglion
Here hormones are released into the blood stream
Secret epinephrine and norepinephrine
Blood is the vehicle which carries these chemical messengers

Sympathetic summary of activation
Increased alertness
Feeling of energy
Increased cardiovascular and respiratory activity
Elevation of muscle tone
Mobilization of energy reserves, breakdown of glycogen in muscle and liver cells and the release of lipids from storage
Figure 16.6 Sympathetic Variosities
Sympathetic summary division.
Two sets of sympathetic chain ganglion
Thee collateral ganglion
Two adrenal medullae
Preganlionic fibers re short
Postganglionic fibers are long
Typical examples of divergence
Single neuron can control many visceral effectors
Preganglionic fibers release ACH
Post ganglionic fibers release NE
Works through secondary messengers

Learning Objectives
Compare the organization of the autonomic nervous system with the somatic nervous system.
Describe the structures and functions of the sympathetic and parasympathetic divisions of the ANS.
Describe the mechanisms of neurotransmitter release in the sympathetic and parasympathetic divisions.
Describe the effects of sympathetic and parasympathetic neurotransmitters on target organs and tissues.
Learning Objectives
Describe the hierarchy of interacting levels of control in the ANS
Explain how memories are created, stored and recalled.
Summarize the effects of aging on the nervous system.
SECTION 16-1 An Overview of the ANS
General information
Neural Integration II: The Autonomic Nervous System and Higher Order Functions
There are going to be two major goals here, compare:
The neural interactions that direct motor output
The subdivisions of the ANS based on structural and functional patters

Common ground
Both the somatic and autonomic nervous systems are efferent that carry motor commands to the skeletal system
In the somatic nervous system the commands form the CNS exert direct control over the the skeletal muscle
In the ANS motor neurons of the CNS synapse on visceral motor neurons in autonomic ganglion and it is through the ganglion that control is exerted

More
The visceral motor neurons of the CNS are known as preganglionic neurons and the axons are called prehanglionic fibers
Those that leave the ganglion are called postganglionic fibers


Somatic or visceral information input
Input can trigger visceral reflexes and these motor commands are distributed by the ANS
ANS (review)
Coordinates cardiovascular, respiratory, digestive, urinary and reproductive functions
Preganglionic neurons in the CNS send axons to synapse on ganglionic neurons in autonomic ganglia outside the CNS
Divisions of the ANS
Most often the divisions have opposing effects
However, some divisions are only controlled by one of the divisions
Sympathetic division (thoracolumbar, "fight or flight")
Thoracic and lumbar segments
Parasympathetic division (craniosacral, "rest and repose")
Preganglionic fibers leaving the brain and sacral segments
A general statement
The parasympathetic nervous system dominates under resting conditions
And the sympathetic nervous system kicks in under times of stress

Eneteric nervous system
Generally local control over digestive properties
But the activity can also be influenced by both the sympathetic and parasympathetic divisions
SECTION 16-2 The Sympathetic Division
Sympathetic division anatomy
Preganglionic neurons between segments T1 and L2
Ganglionic neurons in ganglia near vertebral column
The preganlionic fibers are short and the postganglionic fibers are long
The job is to prepare the body for fight of flight responses
Specialized neurons in adrenal glands
Parasympathetic division
The preganlionic fibers originate in the brain stem and the sacral segments of the spinal cord
They synapse in ganglion which are close to the target organ
This means that the preganlionic fibers are long and the postganglionic fibers are short
Job is to conserve energy
This means that if you consume a heavy meals, the activity is for digestions, absorption, and waste removal
Figure 16.3 The Organization of the Sympathetic Division of the ANS
Sympathetic division
The division consists of preganglionic neurons that are located between segments T1 and L2 of the spinal cord
The cell bodies are located in the gray matter of the lateral gray horns of their axons axons enter the ventral root at three segments

Sympathetic chain ganglion
Can also be called paaravertebral ganglion or lateral ganglion
These are found on both sides of the vertebral column
Innervates body wall, inside the thoracic cavity, and head and limbs

Collateral ganglia
Prevertebral ganglia
Innervates tissues and organs in the abdominopelvic cavity


Adrenal medullae
The center of each adrenal gland
Neurotransmitters released directly into the blood stream
Figure 16.4 Sympathetic Pathways
Figure 16.4 Sympathetic Pathways
Figure 16.4 Sympathetic Pathways
Sympathetic chain ganglion
Preganglionic fibers that carry motor commands that target structures in the body wall, thoracic cavity, or in the head, neck, or limbs, it will synapse in one or more sympathetic chain ganglion
Postganglionic fibers paths will differ
Postganglionic fibers
These control effectors in the body wall, head, neck, limbs

Organization and anatomy of the sympathetic division
The T1 and L2 spinal segments contain sympathetic preganglionic fibers
These segments of T1-L2, ventral roots give rise to myelinated white ramus
Which then lead to sympathetic chain ganglia or in the adrenal medulla
Sympathetic chain ganglia
Two final routes
Postganglionic fibers which control visceral effectors in wall, head, neck, or limbs
Potganglionic fibers which innervate structures of the heart and lungs form sympathetic nerves


Summary
The cervical, inferior lumbar, and sacral chain receive preganglionic innervation by preganglionic fibers from spinal segments T1 – L2 and every spinal nerve receives a gray ramus from a ganglionic of the sympathetic chain
Only the thoracic and superior lumbar ganglion T1 – L2 receive preganglionic fibers from white rami
Every spibal nerve receives gray ramus from a ganglion of the sympathetic chain
Collateral Ganglia
Figure 16.5 The Distribution of Sympathetic Innervation
Postganglionic fibers
Rejoin spinal nerves and reach their destination by way of the dorsal and ventral rami
Those targeting structures in the thoracic cavity form sympathetic nerves
Go directly to their destination
Abdominopelvic viscera
Sympathetic innervation via preganglionic fibers synapse within collateral ganglia
Splanchic nerves
Abdominopelvic viscera
Celiac ganglion
Innervates stomach, liver, gall bladder, pancreas, spleen
Superior mesenteric ganglion
Innervates small intestine and initial portion of large intestine
Inferior mesenteric ganglion
Innervates kidney, urinary bladder, sex organs, and final portion of large intestine
Sympathetic activation
In crises, the entire sympathetic division responds
Sympathetic activation
Affects include increased alertness, energy and euphoria, increased cardiovascular and respiratory activities, elevation in muscle tone, mobilization of energy resources
Neurotransmitters and sympathetic function
Stimulation of sympathetic division has two distinct results
Release of ACh or NE at specific locations
Secretion of E and NE into general circulation
Most postganglionic fibers are adrenergic, a few are cholinergic or nitroxidergic
Two types of receptors are alpha receptors and beta receptors
Sympathetic ganglionic neurons end in telodendria studded with varicosities filled with neurotransmitter
Adrenal Medullae
Preganglionic fibers enter an adrenal gland and proceed to its center, which is called adrenal medulla
This is a sympathetic ganglion
Here hormones are released into the blood stream
Secret epinephrine and norepinephrine
Blood is the vehicle which carries these chemical messengers

Sympathetic summary of activation
Increased alertness
Feeling of energy
Increased cardiovascular and respiratory activity
Elevation of muscle tone
Mobilization of energy reserves, breakdown of glycogen in muscle and liver cells and the release of lipids from storage
Figure 16.6 Sympathetic Variosities
Sympathetic summary division.
Two sets of sympathetic chain ganglion
Thee collateral ganglion
Two adrenal medullae
Preganlionic fibers re short
Postganglionic fibers are long
Typical examples of divergence
Single neuron can control many visceral effectors
Preganglionic fibers release ACH
Post ganglionic fibers release NE
Works through secondary messengers

Chapter 15, part 2
Neural Integration I: Sensory Pathways and the Somatic Nervous System
SECTION 15-3 The Organization of Sensory Pathways
First, second, and third order neurons
First order neurons
Sensory neurons that deliver sensory information to the CNS
Second order neurons
First order neurons synapse on these in the brain or spinal cord
Third order neurons
Found in the thalamus
Second order neurons synapse on these
First order neuron
Delivers sensations to the CNS
The cell body is found in the dorsal root ganglion or the cranial root ganglion
Second order neuron
Often found in the spinal cord or the brain stem
If the sensation is to reach our CNS, then the information must be posted to a third order neuron
Third order neuron
Found in the thalamus
These synapse on sensory areas of the primary sensory cortex

Somatic sensory pathways: divisions
Three major pathways carry sensory information
Posterior column pathway
Anterolateral pathway
Spinocerebellar pathway
Figure 15.6 Sensory Pathways and Ascending Tracts in the Spinal Cord
Posterior column pathway
Carries fine touch, pressure and proprioceptive sensations
Axons ascend within the fasciculus gracilis and fasciculus cuneatus
Relay information to the thalamus via the medial lemniscus
Decussation occurs
How do we locate?
Our ability to determine where something is happening depends on the projection of information to the thalamus to the primary sensory cortex
Sensory information for head and toe arrive at different locations
Without this you could determine light touch but not location
The number of receptors is not determined by the size of the area, the face has more sensory response then the back
The tongue has many more receptors then the back
Figure 15.8 The Posterior Column Pathway and the Spinothalamic Tracts
Anteriorlateral pathways
Conscious sensations of poorly located touch, pressure, pain, and temperature
First order neurons enter the spinal cord synapse on second order neurons in the posterior gray horn
These axons cross to the opposite side of the spinal cord before ascending
This pathway delivers sensations to the reflex centers of the brain stem and then on to the cerebral cortex
The anterior spinothalamic tracts carry crude touch and pressure
The lateral spinothalamic tracts carry pain and temperature
Both of these end on third order neurons in the thalamus
Them relayed to primary sensory cortex regions
Figure 15.8 The Posterior Column Pathway and the Spinothalamic Tracts
Spinocerebellar pathway
Includes the posterior and anterior spinocerebellar tracts
Carries sensation to the cerebellum concerning position of muscles, tendons and joints to the cerebellum
Information does not reach conscious awareness
Axons of first order neurons synapse on interneurons of the gray horns
These second order neurons ascend in two tracts: posterior spinocerebellar and anterior spinocerebellar
Figure 15.9 The Spinocerebellar Pathway
Visceral sensory pathways
Carry information collected by interoceptors
Most of the information collected from cranial nerves V, VII, IX and X delivered to solitary nucleus in medulla oblongata
Dorsal roots of spinal nerves T1 – L2 carry visceral sensory information from organs between the diaphragm and pelvis
Dorsal roots of spinal nerves S2 – S4 carry sensory information below this area
Most information never reaches the primary sensory cortex so we generally remain unaware of these sensations

What kind of receptors are there?
Nociceptors
Thermorecptors
Tactile receptors
Baroreceptors
chemoreceptors
SECTION 15-4 The Somatic Nervous System
Objectives
Describe the components, processes, and functions of the somatic pathways
Describe the levels of information processing involved in motor control
Somatic Motor pathways General
Motor commands issued by the CNS are distributed by the somatic nervous system and the autonomic nervous system
The SAS controls the contractions of skeletal muscle and is under voluntary control
The ANS is responsible for visceral control, or involuntary control
Somatic motor pathways
Upper motor neuron
Cell body lies in a CNS processing center
Lower motor neuron
Cell body located in a motor nucleus of the brain or spinal cord
Figure 15.10 Descending (Motor) Tracts in the Spinal Cord
The corticospinal pathway
Also called the pyramidal system
Provides voluntary skeletal muscle control
This is a direct pathway upper on lower neurons
Also can be indirect by innervating medial and lateral pathways
Corticobulbar tracts terminate at cranial nerve nuclei
Corticospinal tracts synapse on lower motor neurons in the anterior gray horns of the spinal cord
Visible along medulla as pyramids
The three cortisospinal tracts
Corticobullar
Lateral cortiospinal
Anterior corticospinal

Corticobullar tracts
Synapses on lower motor neurons
III, IV, VI, VII, IX, XI, and XII
Provide conscious control over skeletal muscle that move the eye, face, jaw, neck, and pharynx

Corticospinal tracts
Synapse on lower motor neurons in gray horn of spinal cord
These are visible as thick bands of neurons called the pyramids
These tracts then cross over to the other side to enter the descending lateral corticospinal on the opposite side of the cord
The rest continue on the same side of anterior corticospinal tracts
Pyramids (review)
Most of the axons decussate to enter the descending lateral corticospinal tracts
Those that do not cross over enter the anterior corticospinal tracts
Provide rapid direct method for controlling skeletal muscle
Figure 15.11 The Corticospinal Pathway
The Motor homunculus
This is the map region of motor activities
The proportions of motor homunculus are different then the parts of the body they effect
The area is proportional to the number of motor units present in that area
The finer the motor control, the more motor units affected, therefore that area has a larger motor homunculus
The medial and lateral pathways
Several centers in the cerebrum, diencephalon, and brain stem issue somatic motor commands as the result of processing at the subconscious level
These are known as being extrapyramidal system (ESP)
They are better described as being:
The medial and lateral pathways
Issue motor commands as a result of subconscious processing
They can modify or direct muscle contractions by stimulating, facilitating or inhibiting lower motor neurons
What are these connections like?
Axons of the upper motor neurons in the lateral and medial pathways synapse on the same lower motor neurons innervated by the corticospinal pathway
This means that there is dual motor control, primary motor cortex and brain stem but also at the level of the lower motor neuron
Medial pathway
Its job is the primar control of gross movements of the trunk and proximal limbs
The upper motor neurons are located in the:
Receive information over the vestibular-cochlear nerve (VIII) from receptors in the inner ear that monitor position and movement of the head
Primary goal is to maintain posture and balance
The descending fibers in the spinal cord constitute the vestibulospinal tracts

Tectospinal tracts
These arise out of the colliculi
These receive sensory information
Motor axons here descend through this tract
They cross over before they synapse on the lower motor neurons

Reticulospinal tracts
This is a loose network which extend throughout the brain stem
Receives input from all ascending and descending pathways
It has extensive connections with the cerebrum, cerebellum and the brain stem
The axons of the upper motor neurons of the reticular formation descend through this pathway
Different areas control different areas also
lateral pathways
Lateral pathway
Controls muscle tone and movements of the distal muscles of the upper limbs but not as significant as those of the lateral corticospinal tracts
Important in maintaining motor control and muscle tone in upper limbs if the corticospinal pathways are damaged
They upper motor neurons lie within the red nuclei of the mesencephalon
This neurons cross over to the other side and descent through the rubrospinal tracts and extend only to the cervical spinal cord
Job of the baal nuclei and the cerebellum
The coordination and feedback control over muscle contractions for both conscious and subconscious activity
The basal nuclei
Responsible for the background pattern movements
This is especially true of rhythmic cyclic patterns movement for walking and running
They adjust the activity of the upper motor neurons based on the information provided by the cerebral cortex and the substantia nigra

Two basic nuclei exist
One group synapse on the thalamic neurons which send their axons to the premotor cortex association center that will direct the activity of the primary motor cortex
This controls the information passed on the corticospinal tract
The second group
Synapse on the reticular formation altering inhibitory or excitatory activity of the reticulospinal tract

What are the types of neurons that exist?
One the stimulates neurons by releasing Ach
The other inhibits neurons by releasing gamma amino butyric acid

Injury?
The primary motor cortex is responsible for fine motor control over skeletal muscles
Some voluntary movements can be controlled by the basal nuclei, only the movements are not as precise
The cerebellum
The cerebellum monitors proprioceptive, visual, vestibular sensory information
Axons relaying proprioceptive information reach the cerebellar cortex in the spinocebellar tracts
Visual is relayed from the superior colliculi
Balance information is relayed from the vestibullar nuclei
The net result is affecting the upper motor neuron activity of the corticospinal, medial and lateral pathways
More
All motor pathways send information to the cerebellum where the motor commands are issued
Movement then proceeds and is monitored by the cerebellum
The cerebellum adjusts movements based upon proprioceptive and vestibular information received
It is the job of the cerebellum to refine the cerebellar decision to move with the appropriate number of muscle units
The basal nuclei and cerebellum in review
Basal nuclei adjust motor commands issued in other processing centers
Provide background patterns of movement involved in voluntary motor movements
Cerebellum monitors proprioceptive information, visual information and vestibular sensations
Levels of processing and motor control activity
Always remember that these are a series of pathways involving synapses
Many activities are performed without you thinking about doing them
This is all a process may not involve evaluation by the cerebral cortex
Basic functions in the medulla and become more complex in the cerebral cortex at the primary motor center
control and responses
Levels of processing and motor control
Spinal and cranial reflexes provide rapid, involuntary, preprogrammed responses are the first to appear and are directed by the brain stem and mesencephalon in infants
Voluntary responses, learned behaviors are
More complex appear later and require more time to prepare and execute
Figure 15.12 Centers of Somatic Motor Control
During development( review)
Spinal and cranial reflexes are first to appear in infants
Complex reflexes develop as CNS matures and brain grows and more connections are made
More connections are made until age four
The pathways that develop will have long term affects on metal capabilities
You should now be familiar with:
The components of the afferent and efferent divisions of the nervous system, and what is meant by the somatic nervous system.
Why receptors respond to specific stimuli and how the organization of a receptor affects its sensitivity.
The major sensory pathways.
How we can distinguish among sensations that originate in different areas of the body.
The components, processes and functions of the somatic motor pathways.
The levels
of information processing involved in motor control.

Chapter 15, part 1
Neural Integration I: Sensory Pathways and the Somatic Nervous System
Learning Objectives
Specify the components of the afferent and efferent divisions of the nervous system, and explain what is meant by the somatic nervous system.
Explain why receptors respond to specific stimuli and how the organization of a receptor affects its sensitivity.
Identify the major sensory pathways.
Learning Objectives
Explain how we can distinguish among sensations that originate in different areas of the body.
Describe the components, processes and functions of the somatic motor pathways.
Describe the levels of information processing involved in motor control.
SECTION 15-1 An Overview of Sensory Pathways and the Somatic Nervous System
Special senses
These are much more complex receptors then those of the general sense
The receptors are located in sense organs
This information is then distributed to specific regions of the cerebral cortex
Auditory
Visual
Etc

Specialized receptors
In these cases the receptor potential and the generator potential occur in different cells of the sensory neuron
Specialized receptors
Taste
Hearing
Equilibrium
Vision

Neural pathways
Afferent pathways
Sensory information coming from the sensory receptors through peripheral nerves to the spinal cord and on to the brain
Efferent pathways
Motor commands coming from the brain and spinal cord, through peripheral nerves to effecter organs
Figure 15.1 An Overview of Neural Integration
SECTION 15-2 Sensory Receptors and their Classification
What are Receptors
These are specialized cells or cell processes which provide your central nervous system with information about conditions inside and outside of the body
There is a term called general senses which is used to describe our sensitivity to:
Temperature
Pain
Touch
Vibration
Pressure
Proprioception
Sensory Receptors
The goal of a sensory receptor is to collect information and detail it in an action potential for transduction to the central nervous system
This is a graded response, the stronger the potential, the stronger the signal sent to the CNS
However, the receptor potential must be strong enough to generate a action potential

The detection of stimuli
The key here is that the receptors are specific for their job
This is a form of division of labor
A touch receptor would not respond strongly to a chemical stimuli
This is called receptor specificity
The area which is monitored is called the receptive field

What is the receptive field?
Some areas have many receptors and therefore the field is monitored better
If there are fewer receptors, the monitoring is poorer
Regardless of the receptor, information must be sent to the CNS

Sensory receptor
Specialized cell or cell process that monitors specific conditions
Arriving information is a sensation
Awareness of a sensation is a perception
How is specificity determined?
It is the structure of the receptor and its associated structures which determine how the receptor responds
Senses
General senses
Pain
Temperature
Physical distortion
Chemical detection
Receptors for general senses scattered throughout the body
Special senses
Located in specific sense organs
Structurally complex
Sensory receptors
Each receptor cell monitors a specific receptive field
Transduction
A large enough stimulus changes the receptor potential, reaching generator potential
The interpretation of sensory information
Sensory information that arrives at the CNS is routed to the appropriate location depending on the source
Those of touch reach the region called the primary sensory cortex
Those of visual, auditory, gustatory, and olfaction reach appropriate areas of the cortex
Receptors
Tonic receptors
Always active
Slow acting receptors
Phasic receptors
Provide information about the intensity and rate of change of a stimulus
Fast acting receptors
Adaptation
Is defined as the reduction in sensitivity in the presence of a constant stimulus

Fast adapting receptors
Thermoreceptors
temperature
Slow adapting receptors
Noiceptors
Pain

Central adaptation
This occurs from the CNS
Conscious awareness of the stimuli disappears

Peripheral adaptation
This reduces the amount of information which reaches the CNS
Information is processed at the spinal cord or brain stem and might not reach the higher centers of the brain
These often produce reflex motor responses that we are not aware of

Higher centers of control sensitivity
Output from higher centers can increase or decrease receptor sensitivity or facilitate transmission along a sensory pathway
Often involves the mesencephalon and the reticular activating system

General receptor classification
Exteroceptors: external environment
Proprioceptors: skeletal muscle and joints related to position
Interoceptors: monitors visceral organ functions

Detailed Classification of sensory receptors
Noiceptors: pain
Thermoreceptors: temperature
Mechanoreceptors: physical distortion
Chemorecpetors: chemical concentration

Differences
EACH receptor is unique in design
The difference between a somatic and a visceral receptor is location, location, location
A pain receptor in the gut looks like a pain receptor on the surface of the skin
However, the two send their information to different location
Proprioception is purely somatic
The visceral organs have fewer pain, temperature, and touch receptors
Only about 1 percent of the information that reaches the spinal cord or the brain stem actually reaches the CNS
The general senses
Three types of nociceptor
Provide information on pain as related to extremes of temperature
Provide information on pain as related to extremes of mechanical damage
Provide information on pain as related to extremes of dissolved chemicals
Myelinated type A fibers carry fast pain
Slower type C fibers carry slow pain
Theromreceptors
Free nerve endings of the dermis, skeletal muscle, liver, and hypothalamus
Cold receptors more common then hot
No structural difference
They are phasic receptors which send their information to the reticular formation, thalamus, and the primary sensory cortex

Mechanoreceptors
They respond when their cell membranes are distorted
They are often described as being mechanically regulated
They fall into three classes:
Tactile responses
Baroreceptors
Proprioceptors

Tactile receptors
Provide information for:
Touch: shape and texture
Pressure: mechanical distortion
Vibration: pulsating sounds
Touch vs pressure understanding depends on the degree of stimulation
Figure 15.2 Receptors and Receptive Fields
Thermoceptors and mechaniceptors (review)
Found in the dermis
Mechaniceptors
Sensitive to distortion of their membrane
Tactile receptors (six types)
Baroreceptors
Proprioceptors (three groups)
Figure 15.3 Tactile Receptors in the Skin
Tactile receptors of the skin
Fine touch and pressure receptors can provide information about the source of stimulation which can include location, size, shape, texture, and movement because of the narrow receptor fields
Crude touch and pressure provide poor localization because of the large receptor fields
Types:
Free nerve endings:
Root hair plexus:
Tactile discs:
Lamellated discs
Ruffini corpuscles
Free nerve endings
Sensitive to touch and pressure
Described as being tonic with narrow receptor fields
Root hair plexus
Monitor distortions and movements across the body
Sensory dendrites are stimulated and produce action potentials
Adapt rapidly with a narrow receptor field
Tactile discs
Required for fine touch and pressure receptors
Sensitive with very small receptor fields
Tactile Corpuscles
Perceive sensation of fine touch and pressure and low frequency vibration
Typically found in very sensitive areas of the skin
Lamellated corpuscles
Sensitive to deep pressure
Adapt rapidly
Ruffini corpuscles
Sensitive to pressure and distortion of the skin
Tonic receptors without adaption
Baroreceptors
Required for the monitoring of pressure
Consists of free nerve endings found in the wall of an an organ or on the elastic walls of a blood vessel
When there is a change in the elastic walls of a blood vessel an action potential is sent
They are highly adaptive
Major role in the monitoring of cardiac output. Adjust bllood pressure, and lung expansion
There are also stretch receptors in the GI tract as well

Proprioceptors
Monitors the position of joints, tendons, and ligaments and the state of muscle contraction
Muscle spindles
Golgi tendon organs
Receptors in joint capsules

Muscle spindles
Monitors skeletal muscle length
Golgi tendon organs
Location between the skeletal muscle and a tendon
Stimulated by tension in the tendon
Monitors external tension of a muscle
Goal is to prevent tearing
Receptors in joint capsules
Detect pressure, tension, and movement at the joint
Helps regulates your sense of body position with the inner ear

What is the job of chemoreceptors?
They are specialized neurons which can detect small changes in the concentration of specific chemicals or compounds
In general response only to those chemicals which are water soluble
Demonstrate peripheral adaptation and then central adaptation
What they do not do?
They do not send information to the primary sensory cortex
Information is sent to the brain stem which can then alter the respiratory and cardiovascular activities

What do they respond to?
Neurons of the respiratory center of the brain respond to the concentration of hydrogen ions in the blood, that is the blood pH and the carbon dioxide molecule in the CSF
Chemoreceptors
Chemoreceptors: location
Carotid bodies: internal carotid artery
Aortic bodies: aortic arch
Information from here is passed to cranial nerves IX (glossopharyngeal) and X (vagus)
Figure 15.4 Baroreceptors and the Regulation of Visceral Function
Figure 15.5 Chemoreceptors

Chapter 14, part 4
The Brain and Cranial Nerves
Olfactory nerves (I)
Carry sensory information responsible for the sense of smell
Synapse within the olfactory bulb
Figure 14.21 The Olfactory Nerve
cranial nerves II, III, IV
Optic nerves (II)
Carry visual information from special sensory receptors in the eyes
Occulomotor nerves (III)
Primary source of innervation for 4 of the extraocular muscles
Trochlear nerves (IV)
Innervate the superior oblique muscles
Figure 14.23 Cranial Nerves Controlling the Extra-ocular Muscles
cranial nerves V, VI, VII
Trigeminal nerves (V)
Missed nerves with ophthalmic, maxillary and mandibular branches
Abducens nerve (VI)
Innervates the lateral rectus muscles
Facial nerves (VII)
Mixed nerves that control muscles of the face and scalp
Provide pressure sensations over the face
Receive taste information from the tongue
Figure 14.24 The Trigeminal Nerve
Figure 14.25 The Facial Nerve
cranial nerves VIII, IX
Vestibulocochlear nerves (VIII)
Vestibular branch monitors balance, position and movement
Cochlear branch monitors hearing
Glossopharyngeal nerves (IX)
Mixed nerves that innervate the tongue and pharynx
Control the action of swallowing
cranial nerves X
Vagus nerves (X)
Mixed nerves
Vital to the autonomic control of visceral function
Figure 14.26 The Vestibulocochlear Nerve
Figure 14.27 The Glossopharyngeal Nerve
Figure 14.28 The Vagus Nerve
cranial nerves XI, XII
Accessory nerves (XI)
Internal branches
Innervate voluntary swallowing muscles of the soft palate and pharynx
External branches
Control muscles associates with the pectoral girdle
Hypoglossal nerves (XII)
Provide voluntary motor control over tongue movement
Figure 14.29 The Accessory and Hypoglossal Nerve
SECTION 14-10Cranial Reflexes
Cranial reflexes
Involve sensory and motor fibers of cranial nerves
You should now be familiar with:
The major regions of the brain and their functions.
The formation, circulation and functions of the CSF.
The main components of the medulla oblongata, the pons, the cerebellum, the mesencephalon, the diencephalon, and the limbic system and their functions.
The major anatomical subdivisions of the cerebrum.
The motor, sensory and association areas of the cerebral cortex.
Representative examples of cranial reflexes.

Chapter 14, part 3
The Brain and Cranial Nerves
SECTION 14-8The Limbic System
General description
It includes nuclei and tracts along the border of the cerebrum and the diencephalon
This is described as a functional grouping but not a anatomical grouping
The functions include:
Establishing the emotional state
Links the conscious intellectual functions with the conscious and subconscious autonomic functions of the brain stem
Facilitating memory storage and retrieval
This is a system which is designed to want you to do
The limbic system or motivational system includes
Amygdaloid body
Cingulated gyrus
Parahippocampal gyrus
Hippocampus
Fornix
Functions of the limbic system involved emotions and behavioral drives
Amygaloid body
Appears to be an interface between the limbic system, cerebrum, and sensory neurons
Plays a role in the regulation of the heart beat in the fight of flight response

Limbic lobe
Consists of gyri which which are underneath the corpus callosum

Three gyri are present
Cingulate gyrus
Dentate gyrus
Parahippocampus gtrus

Cingulate gyri
Located superior to the corpus callosum

Dentate gyrus
Posterior and inferior portions of the limbic lobe

Parahippocampal gyrus
Also posterior and inferior to the limbic lobe
Fornix
Tract of white matter which connects the white matter of the hippocampus with the hypothalamus
Curves medially and ends at the mamillary body

Figure 14.13 The Limbic System
Figure 14.14 The Brain in Section
Figure 14.14 The Brain in Section
SECTION 14-9The Cerebrum
Cerebrum: General
It is the largest region of the brain
Responsible for thoughts and intellectual functions
Largely involved in the processing of somatic and sensory information
Cerebral cortex: general
The two hemispheres are separated by a deep longitudinal fissure
The hemispheres are connected by white matter called the corpus callosum
Each hemisphere can also be divided into lobes or regions named after the overlying bone component of the skull

Cerebral cortex: general more
Each hemisphere is divided into and anterior( frontal) and posterior( parietal)
section by the central sulcus
The horizontal sulcus separates the frontal lobe from the temporal lobe
The cerebral cortex
The surface contains gyri and sulci or fissures
Longitudinal fissure separates two cerebral hemispheres
Central sulcus separates frontal and parietal lobes
Temporal and occipital lobes also bounded by sulky
Three key points of the cerebral lobes
Each hemisphere receives sensory information from and sends motor commands to the opposite of the body
The two hemispheres have different functions
The assignment of specific function to the brain is imprecise
White matter of the cerebrum: review
Contains association fibers
Commissural fibers
Projection fibers
Association fibers
These connect areas of the neural cortex within a single hemisphere: two types
Shorter association fibers are called arcuate fibers
The longer fibers are called longitudinal fibers which connect the frontal lobe to the other lobes of the same hemisphere
Commissural fibers
These interconnect the two hemispheres and allow for cross communication: two types
Corpus callosum:
These link the two hemisphere together
Anterior commissure:
Link the hemispheres together
Projection fibers
Link the cerebral cortex to the diencephalon, brain stem, cerebellum, and the spinal cord
All projection fibers must pass through the diencephalon
This allows sensory communication to the motor areas which then through descending tracts pass on the appropriate information
Figure 14.15 The White Matter of the Cerebrum
Basal nuclei: general information
This is the other center of the brain outside of conscious levels
These are directed by the basal nuclei
Gray matter within each hemisphere deep to the floor of the ventricle
More
They are gray matter found within white matter
Projection and commissural fibers travel around them nuclei


The basal nuclei
Caudate nucleus
Globus pallidus
Putamen
Control muscle tone and coordinate learned movement patterns
Functions of the basal nuclei
Subconscious control of muscle tone and coordination of learned movement
They do not initiate a movement, but is responsible for that movement to follow a pattern once that movement has begun

The pattern of movement
First information must arrive here from the sensory areas of the cerebral cortex
Processing occurs here
Output from here goes to the thalamus
Information form here go back to the appropriate areas of the cerebral cortex (motor)
Then the cerebral cortex issues the motor commands
Motor and sensory areas of the cortex
Primary motor cortex of the precentral gyrus directs voluntary movements
Primary sensory cortex of the postcentral gyrus receives somatic sensory information
Touch
Pressure
Pain
Taste
Temperature
Figure 14.17 The Cerebral Hemispheres
Association areas
Control our ability to understand sensory information and coordinate a response
Somatic sensory association area
Visual association area
Somatic motor association area
general interpretive and speech areas
General interpretive area
Receives information from all sensory areas
Present only in left hemisphere
Speech center
Regulates patterns of breathing and vocalization
cortex functions and hemispheric differences
Prefrontal cortex
Coordinates information from secondary and special association areas
Performs abstract intellectual functions
Hemispheric differences
Left hemisphere typically contains general interpretive and speech centers and is responsible for language based skills
Right hemisphere is typically responsible for spatial relationships and analyses
Figure 14.18 Hemispheric Lateralization
Electroencephalogram (EEG)
Measures brain activity
Alpha waves = healthy resting adult
Beta waves = concentrating adult
Theta waves = normal children
Delta waves = normal during sleep
Figure 14.19 Brain Waves
Focus: Cranial Nerves
12 pairs of cranial nerves
Each attaches to the ventrolateral surface of the brainstem near the associated sensory or motor nuclei
Figure 14.20 Origins of the Cranial Nerves
Figure 14.20 Origins of the Cranial Nerves
Figure 14.20 Origins of the Cranial Nerves

Chapter 14, part 2
The Brain and Cranial Nerves
SECTION 14-3 The Medulla Oblongata
Medulla oblongata
It is designed to connect the brain and the spinal cord
Contains relay stations and reflex centers
Olivary nuclei
Cardiovascular and respiratory rhythmicity centers
Reticular formation begins in the medulla oblongata and extends into more superior portions of the brainstem
General description
Inferior portion of the medulla oblangota resembles that of the spinal cord with a small central canal
When ascending the medulla toward the brain the central canal opens into the 4th ventricle

Activity
All activity between the brain and the spinal cord involve ascending and descending tracts
Center for the coordination of many complex visceral and autonomic functions

Autonomic nuclei controlling visceral activities
Organized into the reticular formation centers
Responsible for the following
Reflex centers
Cardiovascular centers
Cardiac centers
Vasomotor centers
Respiratory centers

Sensory and Cranial nerves
VIII, IX, X, XI, XII
Motor commands to the pharnyx, neck, back
Commands to the visceral organs
VIII provides auditory information

Relay Stations
Nucleus gracilis and nucleus cuneatus pass information to the thalamus
Solitary nucleus receives visceral information that is passed to the CNS
Olivary nuclei pass information to cerebellar cortex
Figure 14.7 The Diencephalon and Brain Stem
Figure 14.7 The Diencephalon and Brain Stem
Figure 14.8 The Medulla Oblongata and Pons
Figure 14.8 The Medulla Oblongata and Pons
SECTION 14-4 The Pons
The pons contains
Links the cerebellum with the mesencephalon, diencephalon, cerebrum, and spinal cord
Contains sensory and motor nuclei for four cranial nerves
Nuclei that help control respiration
Nuclei and tracts linking the cerebellum with the brain stem, cerebrum and spinal cord
Ascending, descending and transverse tracts
Sensory and Motor nuclei of cranial nerves
V, VI, VII, VIII
Innervate the jaw, anterior surface of the face, lateral rectus muscle, sense organs of the inner ear

Nuclei and control of respiration
Each side of the pons have respiratory centers
Apneustic and pneumotaxic
Modify activity of mendulla oblongata

Nuclei that process information ascending and descending from the Cerebellum
Links the cerebellum with the brain stem, cerebrum, and spinal cord

Ascending, descending, and transverse tracts
Connects the pons with the cerebellar hemisphere of the opposite side

Figure 14.8 The Medulla Oblongata and Pons
Figure 14.8 The Medulla Oblongata and Pons
SECTION 14-5 The Cerebellum
What is it?
It is an automatic processing center with two functions
Adjusting the postural muscle of the back
Programming and fine tuning movements controlled at both the conscious and subconscious levels
Adjusting postural muscles of the body
Coordinates rapid, automatic adjustments that maintain balance and equilibrium
Means alterations in muscle tone
Programming
Refines learned movement patterns
The cerebellum compares the motor commands with sensory information and adjusts to make movements smooth
The cerebellum
Adjusts postural muscles and tunes on-going movements
Cerebellar hemispheres
Anterior and posterior lobes are separated by a primary fissure
Vermis: midline band of cortex tissue
Flocculonodular lobe: lines between roof of the fourth ventricle, cerebellar hemispheres, and verrmis
More on construction
Cerebellum has a superficial layer of neural cortex
Many Purkinje fibers are present which create a tree like appearance called the arbor vitae
More on construction
Superior, middle and inferior cerebellar peduncles link cerebellum with brain stem, diencephalon, cerebrum, and spinal cord
Superior cerebellar peduncles
Link the cerebellum with the midbrain, diencephalon, and the cerebrum


Middle cerebellar penduncles
Connect the cerebellar hemispheres with sensory and motor nuclei in the pons

Inferior cerebellar penduncles
Links the cerebellum to the medulla oblangota and the spinal cord
Figure 14.9 The Cerebellum
Figure 14.9 The Cerebellum
SECTION 14-6The Mesencephalon
Figure 14.10 The Mesencephalon
The composition of the Mesencephalon
Tectum
Walls and floor
White matter
Tectum
Gray matter
Superior colliculi
Integrate visual information with sensory outputs and initiates reflex responses to visual stimuli
Inferior collicul
Gray matter
Relays auditory information to medial geniculate, initiates reflex response to auditory stimuli

Walls and floor
All gray matter
Red nuclei
Subconscious control of upper limb position and back muscle tone
Substantia nigra
Regulates basal nuclei
Recicular formation
Automatic processing of incoming sensations and outgoing motor commands
Help maintain conscious

White matter
Cerebral peduncles
Connects primary motor cortex with motor neurons in brain, and spinal cord
Carries sensory information on ascending tracts to the thalamus
The mesencephalon: review
The tectum (roof) contains the corpora quadrigemina
Superior and inferior colliculi
The mesencephalon contains many nuclei
Red nucleus
Substantia nigra
Cerebral peduncles
RAS headquarters
SECTION 14-7The Diencephalon
General information
Important role in the integration of conscious and subconscious activities for both sensory and motor commands
The diencephalon: divisions
Epithalamus: roof of the diencephalon
Posterior portion contains then pineal gland
melatonin
Thalamus
Hypothalamus
The thalamus
Final relay point for ascending sensory information that will be projected to the primary sensory cortex
Acts as a filter to pass on information
Coordinates the activities of the cerebral cortex and basal nuclei by relaying information between them
The left and the right thalamus are separated by the 3rd ventricle
The thalamus extends from the anterior commissure to the inferior base of the pineal gland
Figure 14.11 The Thalamus
The hypothalamus
Extends from the optic chiasm to the posterior portions of the mamillary bodies
The mamillary bodies process sensory information and are responsible for the motor movements associated with swallowing and chewing
The infundibulum
Area immediately posterior to the optic chiasm
Extends inferiorly from the floor of the hypothalamus
This is a small narrow stalk
Connects to the pituitary glands

What stimulates the hypothalamus?
Sensory information from the cerebrum, brain stem, and spinal cord
Changes in the composition of CSF
Chemical changes in circulating blood

Subconscious control of the skeletal muscle contractions
Directs somatic motor patterns associated with rage, pleasure, pain, and sexual arousal

Control of autonomic functions
Adjusts activity of the pons
Adjusts centers in the medulla which regulate heart beat, blood pressure, and digestive functions

Coordinates activities of nervous and endocrine systems
It inhibits or stimulates endocrine cells in the pituitary gland through the production of regulatory hormones
Anterior lobe of the pituitary

Secretion of hormones
ADH
Oxytocin
Passed onto the posterior lobe of the pituitary
Production of emotions and drives
Conscious and subconscious behavior patterns
Feeding
Thirst
"drives"

Coordinate Voluntary and involuntary functions
Increase in heart rate and blood pressure in fight or flight response

Regulate body temperature
Regulates CNS activities to keep body temperature normal
Body temp falls, preoptic center signals an autonomic cente, a vasomotor center in the medulla to regulate the peripheral blood vessels

Coordination of Circadian Rhythms
Day and night cycle
Sleep and wake cycle
Through the activity of the pineal gland and the reticular formation
Functions of the the hypothalamus in review
Controls somatic motor activities at the subconscious level
Controls autonomic function
Coordinates activities of the endocrine and nervous systems
Secretes hormones
Produces emotions and behavioral drives
Coordinates voluntary and autonomic functions
Regulates body temperature
Coordinates circadian cycles of activity
Figure 14.12 The Hypothalamus in Sagittal Section
Figure 14.12 The Hypothalamus in Sagittal Section

Chapter 12, part 2
Neural tissue
SECTION 12-4 Neurophysiology: Ions and Electrical Signals
Important membrane processes
Resting potential
Graded potential
Action potential
Synaptic activity
Information process
Resting potential
A neural activities begin with a change in the resting potential

Graded potential
A typical localized stimulus with a strength decreasing from the site or origin
Action Potential
Electrical impulse which is propagated across the surface of the membrane but does not diminish in its strength from the source
Synaptic Activity
This involves the release of neurotransmitters such as Ach
These bind to the postsynaptic cell membrane
A graded response is then produced
Information processing
The response of a postsynaptic cell depends on which receptors are activated

Membrane Potential concepts
The intracellular and the extracellular fluids differ in their ionic concentrations
High Na and chloride ions outside the cell
High potassium ion concentration inside the cell
The nerve cell membrane is sided
Ions are not free to move easily from one side to another must move through leak channels
This is true of a cell which is in the resting potential state

Concepts continued
Key:
There is this sided membrane
There is not a equal number of positive and negative changes on each side of the membrane
It is easier for the potassium ions to move out into the ECF then it is for the sodium to move into the cell
This is why the cell pumps out two sodium ions and pumps in three potassium ions
This relationship of unequal charge distribution is responsible for the excess positive charges on the outside of the membrane

Passive forces
Classified as being
Chemical gradient
Electrical gradients
Chemical gradients
The driving forces here are the chemical identity of the ion in question
This is passive diffusion, from high concentration to low concentration without the involvement of energy expenditure
Electrical Gradients
Because the cell membrane is more permeable to potassium ions than sodium ions, there is a net negative charge inside of the membrane due to the presence of negatively charged proteins
This membrane potential difference is measured in mV volts and for nerve cells is – 70 mV
It is the cell membrane which separates the positive and negative volts from each other

The electrochemical gradient
This potential can oppose or reinforce the chemical gradient
This is a measure of those forces, opposites attract and identical repel
In order for the charge to be negative inside the cell, this means that the chemical gradient is the important driving force over the electrical


Active forces: Sodium Potassium Pump
An ATPase
Pumps out three sodium for every three K pumps back in
This is due to the fact that potassium leaks more easily then sodium leaks in through its leak channels
Figure 12.11 An Introduction to the Resting Potential
Figure 12.12 Electrochemical Gradients
What is resting potential?
It is the mV differences between the inside and the outside of the cell due to concentration differences
This is measured when the cell is undisturbed
Remember that this mV potential changes when membrane permeability changes

Membrane Channel classifications
Passive or leak channels
Active or gated channels

Chemically regulated channels

Changes in the transmembrane potential
Membrane contains
Passive (leak) channels that are always open
Active (gated) channels that open and close in response to stimuli
Figure 12.13 Gated Channels
Three types of active channels
Chemically regulated channels
Voltage-regulated channels
Mechanically regulated channels
Chemically regulated channels
Found most of the time on the dendrites and cell body of a neuron
Open or close when they bind neurotransmitters
Wide spread along the surface of neurons


Voltage regulated
Properties of an excitable membrane
Typically found on axons and synaptic terminals
Capable of generating an action potential
Sodium, potassium, and calcium
Mechanically regulated channels
These respond to a mechanical stress
Typically found on dendrites
Typically those that respond to:
Pressure
Touch
vibration
Graded potential: Sodium ions
A change in potential that decreases with distance
Localized depolarization or hyperpolarization
The result of a stimulus acting on a gated channel
The more channels that open, the stronger the response

Graded Potentials: Potassium
Opening this channel has the opposite effect
Have hyperpolarization
This makes the inside of the membrane more negative
This makes the membrane less likely to respond

Information and Graded Potentials
Each neuron on the dendritic side receives a stimuli which responds as a graded potential
Figure 12.14 Graded Potentials
Figure 12.14 Graded Potentials
Figure 12.15 Depolarization and Hyperpolarization
Action Potential
Appears when region of excitable membrane depolarizes to threshold
Steps involved
Membrane depolarization and sodium channel activation
Sodium channel inactivation
Potassium channel activation
Return to normal permeability
Action Potentials
These are propagated changes in the transmembrane potential
Once started will affect the entire length of the membrane

How does it start?
The voltage gated sodium channels must open first
The sodium ions move across the membrane
This changes the voltage difference across the membrane at this site
It then starts the opening of adjacent voltage gated channels
This resembles a dominoes effect

All of none principle
The initial stimulus must be large enough to open the voltage regulated sodium channels
The impulse can only be passed on when the threshold is exceeded
It is the graded local potential which is responsible for the action potential to take place


Generation of action potentials
Depolarization to threshold
Activation of sodium channels and rapid depolarization
Inactivation of the sodium channels and the activation of the potassium channels
Return to normal permeability

Depolarization to threshold
An area of excitable membrane must be depolarized

Activation of Sodium channels and rapid depolarization
When threshold is reached, the sodium channels open
Now the large electrochemical chemical gradient becomes important
The positively charged sodium ions move inside the membrane because they are attracted to the negative charges on the inside of the membrane
The voltage across the membrane is now positive

Inactivation of sodium channels/ activation of potassium channels
At ~ 30 mV the potassium channels open
Interior of the cell membrane has an excess of positive charges
Here the electrical and chemical gradients favor the movement of potassium ions out of the cell
This sudden loss sodium ions pushes the membrane potential back to resting levels

Normal permeability
This occurs only after a brief state of hyperpolarization

Refractory Period
The time that the action potential begins and until the normal resting potential has been established the membrane will not respond normally to an additional stimuli
Divided into absolute and relative refractory segments

Absolute refractory period
When all of the sodium regulated channels are open or inactivated


Relative refractory period
Begin when the sodium channels regain their normal; resting condition
Here another action potential can occur only if the stimuli is additionally strong
This is needed to counter the potassium ion loss


Sodium Potassium pump
This pumps uses ATP
An enzyme called ATPase is required
This keep the balance of sodium and potassium ions proper on the membrane side
There are 3 sodium on the outside for every 2 potassium ions on the inside
Job is to return the sodium potassium extracellular and intracellular concentrations to prestimulation levels

Propagation of Action potentials
Graded potential is in a short section of the membrane
Action potential extends across the length of the entire membrane
The same events take place over and over
This process is called propagation
Figure 12.16 The Generation of an Action Potential
Figure 12.17 The Generation of an Action Potential
Characteristics of action potentials
Generation of action potential follows all-or-none principle
Refractory period lasts from time action potential begins until normal resting potential returns
Continuous propagation
spread of action potential across entire membrane in series of small steps
salutatory propagation
action potential spreads from node to node, skipping internodal membrane
Figure 12.17 Propagation of an Action Potential along an Unmyelinated Axon
Saltatory Propagation
Occurs in a myelinated axon
This means that only the nodes can respond to a stimuli
This means the signal jumps from one internode to another
Figure 12.18 Saltatory Propagation along a Myelinated Axon Part I
Figure 12.18 Saltatory Propagation along a Myelinated Axon Part II
Axon classification
Type A fibers: largest of the axons, myelinated, 300 mph
Type B fibers: myelinated, smaller, 40 mph
Type C fibers: unmyleinated, 2 mph
Based on diameter, myelination and propagation speed
Where do you find them?
Type A fibers carry sensory information to CNS about position, balance, delicate touch, pressure on skin, also include the motor neurons
Type B and C carry information to the CNS about temperature, pressure, pain, general touch and pressure and carry instructions to smooth and cardiac muscle and other peripheral effectors
Type C carries most of the sensory information to the CNS
Muscle action potential versus neural action potential
Muscle tissue has higher resting potential
Muscle tissue action potentials are longer lasting
Muscle tissue has slower propagation of action potentials

Chapter 12, part 2
Neural tissue
SECTION 12-4 Neurophysiology: Ions and Electrical Signals
Important membrane processes
Resting potential
Graded potential
Action potential
Synaptic activity
Information process
Resting potential
A neural activities begin with a change in the resting potential

Graded potential
A typical localized stimulus with a strength decreasing from the site or origin
Action Potential
Electrical impulse which is propagated across the surface of the membrane but does not diminish in its strength from the source
Synaptic Activity
This involves the release of neurotransmitters such as Ach
These bind to the postsynaptic cell membrane
A graded response is then produced
Information processing
The response of a postsynaptic cell depends on which receptors are activated

Membrane Potential concepts
The intracellular and the extracellular fluids differ in their ionic concentrations
High Na and chloride ions outside the cell
High potassium ion concentration inside the cell
The nerve cell membrane is sided
Ions are not free to move easily from one side to another must move through leak channels
This is true of a cell which is in the resting potential state

Concepts continued
Key:
There is this sided membrane
There is not a equal number of positive and negative changes on each side of the membrane
It is easier for the potassium ions to move out into the ECF then it is for the sodium to move into the cell
This is why the cell pumps out two sodium ions and pumps in three potassium ions
This relationship of unequal charge distribution is responsible for the excess positive charges on the outside of the membrane

Passive forces
Classified as being
Chemical gradient
Electrical gradients
Chemical gradients
The driving forces here are the chemical identity of the ion in question
This is passive diffusion, from high concentration to low concentration without the involvement of energy expenditure
Electrical Gradients
Because the cell membrane is more permeable to potassium ions than sodium ions, there is a net negative charge inside of the membrane due to the presence of negatively charged proteins
This membrane potential difference is measured in mV volts and for nerve cells is – 70 mV
It is the cell membrane which separates the positive and negative volts from each other

The electrochemical gradient
This potential can oppose or reinforce the chemical gradient
This is a measure of those forces, opposites attract and identical repel
In order for the charge to be negative inside the cell, this means that the chemical gradient is the important driving force over the electrical


Active forces: Sodium Potassium Pump
An ATPase
Pumps out three sodium for every three K pumps back in
This is due to the fact that potassium leaks more easily then sodium leaks in through its leak channels
Figure 12.11 An Introduction to the Resting Potential
Figure 12.12 Electrochemical Gradients
What is resting potential?
It is the mV differences between the inside and the outside of the cell due to concentration differences
This is measured when the cell is undisturbed
Remember that this mV potential changes when membrane permeability changes

Membrane Channel classifications
Passive or leak channels
Active or gated channels

Chemically regulated channels

Changes in the transmembrane potential
Membrane contains
Passive (leak) channels that are always open
Active (gated) channels that open and close in response to stimuli
Figure 12.13 Gated Channels
Three types of active channels
Chemically regulated channels
Voltage-regulated channels
Mechanically regulated channels
Chemically regulated channels
Found most of the time on the dendrites and cell body of a neuron
Open or close when they bind neurotransmitters
Wide spread along the surface of neurons


Voltage regulated
Properties of an excitable membrane
Typically found on axons and synaptic terminals
Capable of generating an action potential
Sodium, potassium, and calcium
Mechanically regulated channels
These respond to a mechanical stress
Typically found on dendrites
Typically those that respond to:
Pressure
Touch
vibration
Graded potential: Sodium ions
A change in potential that decreases with distance
Localized depolarization or hyperpolarization
The result of a stimulus acting on a gated channel
The more channels that open, the stronger the response

Graded Potentials: Potassium
Opening this channel has the opposite effect
Have hyperpolarization
This makes the inside of the membrane more negative
This makes the membrane less likely to respond

Information and Graded Potentials
Each neuron on the dendritic side receives a stimuli which responds as a graded potential
Figure 12.14 Graded Potentials
Figure 12.14 Graded Potentials
Figure 12.15 Depolarization and Hyperpolarization
Action Potential
Appears when region of excitable membrane depolarizes to threshold
Steps involved
Membrane depolarization and sodium channel activation
Sodium channel inactivation
Potassium channel activation
Return to normal permeability
Action Potentials
These are propagated changes in the transmembrane potential
Once started will affect the entire length of the membrane

How does it start?
The voltage gated sodium channels must open first
The sodium ions move across the membrane
This changes the voltage difference across the membrane at this site
It then starts the opening of adjacent voltage gated channels
This resembles a dominoes effect

All of none principle
The initial stimulus must be large enough to open the voltage regulated sodium channels
The impulse can only be passed on when the threshold is exceeded
It is the graded local potential which is responsible for the action potential to take place


Generation of action potentials
Depolarization to threshold
Activation of sodium channels and rapid depolarization
Inactivation of the sodium channels and the activation of the potassium channels
Return to normal permeability

Depolarization to threshold
An area of excitable membrane must be depolarized

Activation of Sodium channels and rapid depolarization
When threshold is reached, the sodium channels open
Now the large electrochemical chemical gradient becomes important
The positively charged sodium ions move inside the membrane because they are attracted to the negative charges on the inside of the membrane
The voltage across the membrane is now positive

Inactivation of sodium channels/ activation of potassium channels
At ~ 30 mV the potassium channels open
Interior of the cell membrane has an excess of positive charges
Here the electrical and chemical gradients favor the movement of potassium ions out of the cell
This sudden loss sodium ions pushes the membrane potential back to resting levels

Normal permeability
This occurs only after a brief state of hyperpolarization

Refractory Period
The time that the action potential begins and until the normal resting potential has been established the membrane will not respond normally to an additional stimuli
Divided into absolute and relative refractory segments

Absolute refractory period
When all of the sodium regulated channels are open or inactivated


Relative refractory period
Begin when the sodium channels regain their normal; resting condition
Here another action potential can occur only if the stimuli is additionally strong
This is needed to counter the potassium ion loss


Sodium Potassium pump
This pumps uses ATP
An enzyme called ATPase is required
This keep the balance of sodium and potassium ions proper on the membrane side
There are 3 sodium on the outside for every 2 potassium ions on the inside
Job is to return the sodium potassium extracellular and intracellular concentrations to prestimulation levels

Propagation of Action potentials
Graded potential is in a short section of the membrane
Action potential extends across the length of the entire membrane
The same events take place over and over
This process is called propagation
Figure 12.16 The Generation of an Action Potential
Figure 12.17 The Generation of an Action Potential
Characteristics of action potentials
Generation of action potential follows all-or-none principle
Refractory period lasts from time action potential begins until normal resting potential returns
Continuous propagation
spread of action potential across entire membrane in series of small steps
salutatory propagation
action potential spreads from node to node, skipping internodal membrane
Figure 12.17 Propagation of an Action Potential along an Unmyelinated Axon
Saltatory Propagation
Occurs in a myelinated axon
This means that only the nodes can respond to a stimuli
This means the signal jumps from one internode to another
Figure 12.18 Saltatory Propagation along a Myelinated Axon Part I
Figure 12.18 Saltatory Propagation along a Myelinated Axon Part II
Axon classification
Type A fibers: largest of the axons, myelinated, 300 mph
Type B fibers: myelinated, smaller, 40 mph
Type C fibers: unmyleinated, 2 mph
Based on diameter, myelination and propagation speed
Where do you find them?
Type A fibers carry sensory information to CNS about position, balance, delicate touch, pressure on skin, also include the motor neurons
Type B and C carry information to the CNS about temperature, pressure, pain, general touch and pressure and carry instructions to smooth and cardiac muscle and other peripheral effectors
Type C carries most of the sensory information to the CNS
Muscle action potential versus neural action potential
Muscle tissue has higher resting potential
Muscle tissue action potentials are longer lasting
Muscle tissue has slower propagation of action potentials

Chapter 12, part 2
Neural tissue
SECTION 12-4 Neurophysiology: Ions and Electrical Signals
Important membrane processes
Resting potential
Graded potential
Action potential
Synaptic activity
Information process
Resting potential
A neural activities begin with a change in the resting potential

Graded potential
A typical localized stimulus with a strength decreasing from the site or origin
Action Potential
Electrical impulse which is propagated across the surface of the membrane but does not diminish in its strength from the source
Synaptic Activity
This involves the release of neurotransmitters such as Ach
These bind to the postsynaptic cell membrane
A graded response is then produced
Information processing
The response of a postsynaptic cell depends on which receptors are activated

Membrane Potential concepts
The intracellular and the extracellular fluids differ in their ionic concentrations
High Na and chloride ions outside the cell
High potassium ion concentration inside the cell
The nerve cell membrane is sided
Ions are not free to move easily from one side to another must move through leak channels
This is true of a cell which is in the resting potential state

Concepts continued
Key:
There is this sided membrane
There is not a equal number of positive and negative changes on each side of the membrane
It is easier for the potassium ions to move out into the ECF then it is for the sodium to move into the cell
This is why the cell pumps out two sodium ions and pumps in three potassium ions
This relationship of unequal charge distribution is responsible for the excess positive charges on the outside of the membrane

Passive forces
Classified as being
Chemical gradient
Electrical gradients
Chemical gradients
The driving forces here are the chemical identity of the ion in question
This is passive diffusion, from high concentration to low concentration without the involvement of energy expenditure
Electrical Gradients
Because the cell membrane is more permeable to potassium ions than sodium ions, there is a net negative charge inside of the membrane due to the presence of negatively charged proteins
This membrane potential difference is measured in mV volts and for nerve cells is – 70 mV
It is the cell membrane which separates the positive and negative volts from each other

The electrochemical gradient
This potential can oppose or reinforce the chemical gradient
This is a measure of those forces, opposites attract and identical repel
In order for the charge to be negative inside the cell, this means that the chemical gradient is the important driving force over the electrical


Active forces: Sodium Potassium Pump
An ATPase
Pumps out three sodium for every three K pumps back in
This is due to the fact that potassium leaks more easily then sodium leaks in through its leak channels
Figure 12.11 An Introduction to the Resting Potential
Figure 12.12 Electrochemical Gradients
What is resting potential?
It is the mV differences between the inside and the outside of the cell due to concentration differences
This is measured when the cell is undisturbed
Remember that this mV potential changes when membrane permeability changes

Membrane Channel classifications
Passive or leak channels
Active or gated channels

Chemically regulated channels

Changes in the transmembrane potential
Membrane contains
Passive (leak) channels that are always open
Active (gated) channels that open and close in response to stimuli
Figure 12.13 Gated Channels
Three types of active channels
Chemically regulated channels
Voltage-regulated channels
Mechanically regulated channels
Chemically regulated channels
Found most of the time on the dendrites and cell body of a neuron
Open or close when they bind neurotransmitters
Wide spread along the surface of neurons


Voltage regulated
Properties of an excitable membrane
Typically found on axons and synaptic terminals
Capable of generating an action potential
Sodium, potassium, and calcium
Mechanically regulated channels
These respond to a mechanical stress
Typically found on dendrites
Typically those that respond to:
Pressure
Touch
vibration
Graded potential: Sodium ions
A change in potential that decreases with distance
Localized depolarization or hyperpolarization
The result of a stimulus acting on a gated channel
The more channels that open, the stronger the response

Graded Potentials: Potassium
Opening this channel has the opposite effect
Have hyperpolarization
This makes the inside of the membrane more negative
This makes the membrane less likely to respond

Information and Graded Potentials
Each neuron on the dendritic side receives a stimuli which responds as a graded potential
Figure 12.14 Graded Potentials
Figure 12.14 Graded Potentials
Figure 12.15 Depolarization and Hyperpolarization
Action Potential
Appears when region of excitable membrane depolarizes to threshold
Steps involved
Membrane depolarization and sodium channel activation
Sodium channel inactivation
Potassium channel activation
Return to normal permeability
Action Potentials
These are propagated changes in the transmembrane potential
Once started will affect the entire length of the membrane

How does it start?
The voltage gated sodium channels must open first
The sodium ions move across the membrane
This changes the voltage difference across the membrane at this site
It then starts the opening of adjacent voltage gated channels
This resembles a dominoes effect

All of none principle
The initial stimulus must be large enough to open the voltage regulated sodium channels
The impulse can only be passed on when the threshold is exceeded
It is the graded local potential which is responsible for the action potential to take place


Generation of action potentials
Depolarization to threshold
Activation of sodium channels and rapid depolarization
Inactivation of the sodium channels and the activation of the potassium channels
Return to normal permeability

Depolarization to threshold
An area of excitable membrane must be depolarized

Activation of Sodium channels and rapid depolarization
When threshold is reached, the sodium channels open
Now the large electrochemical chemical gradient becomes important
The positively charged sodium ions move inside the membrane because they are attracted to the negative charges on the inside of the membrane
The voltage across the membrane is now positive

Inactivation of sodium channels/ activation of potassium channels
At ~ 30 mV the potassium channels open
Interior of the cell membrane has an excess of positive charges
Here the electrical and chemical gradients favor the movement of potassium ions out of the cell
This sudden loss sodium ions pushes the membrane potential back to resting levels

Normal permeability
This occurs only after a brief state of hyperpolarization

Refractory Period
The time that the action potential begins and until the normal resting potential has been established the membrane will not respond normally to an additional stimuli
Divided into absolute and relative refractory segments

Absolute refractory period
When all of the sodium regulated channels are open or inactivated


Relative refractory period
Begin when the sodium channels regain their normal; resting condition
Here another action potential can occur only if the stimuli is additionally strong
This is needed to counter the potassium ion loss


Sodium Potassium pump
This pumps uses ATP
An enzyme called ATPase is required
This keep the balance of sodium and potassium ions proper on the membrane side
There are 3 sodium on the outside for every 2 potassium ions on the inside
Job is to return the sodium potassium extracellular and intracellular concentrations to prestimulation levels

Propagation of Action potentials
Graded potential is in a short section of the membrane
Action potential extends across the length of the entire membrane
The same events take place over and over
This process is called propagation
Figure 12.16 The Generation of an Action Potential
Figure 12.17 The Generation of an Action Potential
Characteristics of action potentials
Generation of action potential follows all-or-none principle
Refractory period lasts from time action potential begins until normal resting potential returns
Continuous propagation
spread of action potential across entire membrane in series of small steps
salutatory propagation
action potential spreads from node to node, skipping internodal membrane
Figure 12.17 Propagation of an Action Potential along an Unmyelinated Axon
Saltatory Propagation
Occurs in a myelinated axon
This means that only the nodes can respond to a stimuli
This means the signal jumps from one internode to another
Figure 12.18 Saltatory Propagation along a Myelinated Axon Part I
Figure 12.18 Saltatory Propagation along a Myelinated Axon Part II
Axon classification
Type A fibers: largest of the axons, myelinated, 300 mph
Type B fibers: myelinated, smaller, 40 mph
Type C fibers: unmyleinated, 2 mph
Based on diameter, myelination and propagation speed
Where do you find them?
Type A fibers carry sensory information to CNS about position, balance, delicate touch, pressure on skin, also include the motor neurons
Type B and C carry information to the CNS about temperature, pressure, pain, general touch and pressure and carry instructions to smooth and cardiac muscle and other peripheral effectors
Type C carries most of the sensory information to the CNS
Muscle action potential versus neural action potential
Muscle tissue has higher resting potential
Muscle tissue action potentials are longer lasting
Muscle tissue has slower propagation of action potentials

Chapter 12, part 2
Neural tissue
SECTION 12-4 Neurophysiology: Ions and Electrical Signals
Important membrane processes
Resting potential
Graded potential
Action potential
Synaptic activity
Information process
Resting potential
A neural activities begin with a change in the resting potential

Graded potential
A typical localized stimulus with a strength decreasing from the site or origin
Action Potential
Electrical impulse which is propagated across the surface of the membrane but does not diminish in its strength from the source
Synaptic Activity
This involves the release of neurotransmitters such as Ach
These bind to the postsynaptic cell membrane
A graded response is then produced
Information processing
The response of a postsynaptic cell depends on which receptors are activated

Membrane Potential concepts
The intracellular and the extracellular fluids differ in their ionic concentrations
High Na and chloride ions outside the cell
High potassium ion concentration inside the cell
The nerve cell membrane is sided
Ions are not free to move easily from one side to another must move through leak channels
This is true of a cell which is in the resting potential state

Concepts continued
Key:
There is this sided membrane
There is not a equal number of positive and negative changes on each side of the membrane
It is easier for the potassium ions to move out into the ECF then it is for the sodium to move into the cell
This is why the cell pumps out two sodium ions and pumps in three potassium ions
This relationship of unequal charge distribution is responsible for the excess positive charges on the outside of the membrane

Passive forces
Classified as being
Chemical gradient
Electrical gradients
Chemical gradients
The driving forces here are the chemical identity of the ion in question
This is passive diffusion, from high concentration to low concentration without the involvement of energy expenditure
Electrical Gradients
Because the cell membrane is more permeable to potassium ions than sodium ions, there is a net negative charge inside of the membrane due to the presence of negatively charged proteins
This membrane potential difference is measured in mV volts and for nerve cells is – 70 mV
It is the cell membrane which separates the positive and negative volts from each other

The electrochemical gradient
This potential can oppose or reinforce the chemical gradient
This is a measure of those forces, opposites attract and identical repel
In order for the charge to be negative inside the cell, this means that the chemical gradient is the important driving force over the electrical


Active forces: Sodium Potassium Pump
An ATPase
Pumps out three sodium for every three K pumps back in
This is due to the fact that potassium leaks more easily then sodium leaks in through its leak channels
Figure 12.11 An Introduction to the Resting Potential
Figure 12.12 Electrochemical Gradients
What is resting potential?
It is the mV differences between the inside and the outside of the cell due to concentration differences
This is measured when the cell is undisturbed
Remember that this mV potential changes when membrane permeability changes

Membrane Channel classifications
Passive or leak channels
Active or gated channels

Chemically regulated channels

Changes in the transmembrane potential
Membrane contains
Passive (leak) channels that are always open
Active (gated) channels that open and close in response to stimuli
Figure 12.13 Gated Channels
Three types of active channels
Chemically regulated channels
Voltage-regulated channels
Mechanically regulated channels
Chemically regulated channels
Found most of the time on the dendrites and cell body of a neuron
Open or close when they bind neurotransmitters
Wide spread along the surface of neurons


Voltage regulated
Properties of an excitable membrane
Typically found on axons and synaptic terminals
Capable of generating an action potential
Sodium, potassium, and calcium
Mechanically regulated channels
These respond to a mechanical stress
Typically found on dendrites
Typically those that respond to:
Pressure
Touch
vibration
Graded potential: Sodium ions
A change in potential that decreases with distance
Localized depolarization or hyperpolarization
The result of a stimulus acting on a gated channel
The more channels that open, the stronger the response

Graded Potentials: Potassium
Opening this channel has the opposite effect
Have hyperpolarization
This makes the inside of the membrane more negative
This makes the membrane less likely to respond

Information and Graded Potentials
Each neuron on the dendritic side receives a stimuli which responds as a graded potential
Figure 12.14 Graded Potentials
Figure 12.14 Graded Potentials
Figure 12.15 Depolarization and Hyperpolarization
Action Potential
Appears when region of excitable membrane depolarizes to threshold
Steps involved
Membrane depolarization and sodium channel activation
Sodium channel inactivation
Potassium channel activation
Return to normal permeability
Action Potentials
These are propagated changes in the transmembrane potential
Once started will affect the entire length of the membrane

How does it start?
The voltage gated sodium channels must open first
The sodium ions move across the membrane
This changes the voltage difference across the membrane at this site
It then starts the opening of adjacent voltage gated channels
This resembles a dominoes effect

All of none principle
The initial stimulus must be large enough to open the voltage regulated sodium channels
The impulse can only be passed on when the threshold is exceeded
It is the graded local potential which is responsible for the action potential to take place


Generation of action potentials
Depolarization to threshold
Activation of sodium channels and rapid depolarization
Inactivation of the sodium channels and the activation of the potassium channels
Return to normal permeability

Depolarization to threshold
An area of excitable membrane must be depolarized

Activation of Sodium channels and rapid depolarization
When threshold is reached, the sodium channels open
Now the large electrochemical chemical gradient becomes important
The positively charged sodium ions move inside the membrane because they are attracted to the negative charges on the inside of the membrane
The voltage across the membrane is now positive

Inactivation of sodium channels/ activation of potassium channels
At ~ 30 mV the potassium channels open
Interior of the cell membrane has an excess of positive charges
Here the electrical and chemical gradients favor the movement of potassium ions out of the cell
This sudden loss sodium ions pushes the membrane potential back to resting levels

Normal permeability
This occurs only after a brief state of hyperpolarization

Refractory Period
The time that the action potential begins and until the normal resting potential has been established the membrane will not respond normally to an additional stimuli
Divided into absolute and relative refractory segments

Absolute refractory period
When all of the sodium regulated channels are open or inactivated


Relative refractory period
Begin when the sodium channels regain their normal; resting condition
Here another action potential can occur only if the stimuli is additionally strong
This is needed to counter the potassium ion loss


Sodium Potassium pump
This pumps uses ATP
An enzyme called ATPase is required
This keep the balance of sodium and potassium ions proper on the membrane side
There are 3 sodium on the outside for every 2 potassium ions on the inside
Job is to return the sodium potassium extracellular and intracellular concentrations to prestimulation levels

Propagation of Action potentials
Graded potential is in a short section of the membrane
Action potential extends across the length of the entire membrane
The same events take place over and over
This process is called propagation
Figure 12.16 The Generation of an Action Potential
Figure 12.17 The Generation of an Action Potential
Characteristics of action potentials
Generation of action potential follows all-or-none principle
Refractory period lasts from time action potential begins until normal resting potential returns
Continuous propagation
spread of action potential across entire membrane in series of small steps
salutatory propagation
action potential spreads from node to node, skipping internodal membrane
Figure 12.17 Propagation of an Action Potential along an Unmyelinated Axon
Saltatory Propagation
Occurs in a myelinated axon
This means that only the nodes can respond to a stimuli
This means the signal jumps from one internode to another
Figure 12.18 Saltatory Propagation along a Myelinated Axon Part I
Figure 12.18 Saltatory Propagation along a Myelinated Axon Part II
Axon classification
Type A fibers: largest of the axons, myelinated, 300 mph
Type B fibers: myelinated, smaller, 40 mph
Type C fibers: unmyleinated, 2 mph
Based on diameter, myelination and propagation speed
Where do you find them?
Type A fibers carry sensory information to CNS about position, balance, delicate touch, pressure on skin, also include the motor neurons
Type B and C carry information to the CNS about temperature, pressure, pain, general touch and pressure and carry instructions to smooth and cardiac muscle and other peripheral effectors
Type C carries most of the sensory information to the CNS
Muscle action potential versus neural action potential
Muscle tissue has higher resting potential
Muscle tissue action potentials are longer lasting
Muscle tissue has slower propagation of action potentials

Chapter 13, part 3
The Spinal Cord and Spinal Nerves
SECTION 13-4 Principles of Functional Organization
General information
The human body has 10 million sensory neurons
500,000 million motor neurons
20 billion interneurons
General organization
Sensory neurons
Deliver information to CNS
Motor neurons
Distribute commands to peripheral effectors
Interneurons
Interpret information and coordinate responses
Neuronal pools
The billions of interneurons are organized into much smaller units called the neuronal pools
Which are the functional group of interconnected neurons
Each have a limited number of input sources and output destinations
Each may contain both inhibitory and excitatory neurons
The output of one neuronal pool may be inhibitory or excitatory on another neuronal pool
Types of neuronal pools
Neural circuit patterns
Divergence
Convergence
Serial processing
Parallel processing
Reverberation
Figure 13.15 The Organization of Neuronal Pools
Divergence
This is the spread of information from one neuron to many neurons
Or form one pool to many pools
Often found where sensory neurons bring information to the CNS for the information to be distributed to neuronal pools in the spinal cord and the brain

Convergence
Several neurons synapse on the same post synaptic neuron
This means that several patterns of activity in a presynaptic neuron can therefore have the same effect on the same postsynaptic neuron
This means that both conscious and subconscious activity can be directed to the same muscle
diaphragm
Serial processing
Information being relayed in a stepwise fashion
Typical of sensory processing when information is moved form one part of the brain to the other

Parallel Processing
This occurs when several neuronal pools access the same information at the same time
Typical of a pain reflex arc as when you step on a sharp nail


Reverberation
Often described as a form of positive feedback
This causes an amplification of a signal
Common examples
Normal breathing
Muscle coordination
Maintain conscious
An introduction to reflexes
Reflexes are rapid automatic responses to stimuli to maintain homeostasis by making rapid adjustments in the functions of organs and organ systems
A response with little variability
The same response is usually produced from the same stimuli
How is this defined?
Receptor
Integration center
An effector

The response
The neural reflex involves sensory fibers to CNS and motor fibers to effectors
Reflex arc: composition
Wiring of a neural reflex
Five steps
Arrival of stimulus and activation of receptor
Activation of sensory neuron
Information processing
Activation of motor neuron
Response by an effector
Step 1: the arrival of a stimulus and activation on a receptor
The receptor must be either a specialized cell or the dendrites of a a sensory neuron
These receptors are sensitive to physical or chemical changes in the body or the external environment

Step2: Activation of a sensory neuron
Stimulation of pain receptors leads to the formation of propagation of an action potential along the axons of the sensory neurons
The information reaches the spinal cord via the dorsal root
Step 3: Information processing
This stage begins when there is a release of neurotransmitters from the synaptic bulb and arrive at the postsynaptic membrane of the interneuron
This results in an EPSP which is integrated with other stimuli arriving at the postsynaptic neuron
Step 4: activation of a motor neuron
Once the information is received, motor neurons carry action potentials through the ventral root of the spinal nerve

Step 5: response of a peripheral receptor
The action potential causes a release of neurotransmitters in the synaptic cleft which leads to a response by a peripheral receptor
This pull back reflex form something hot is typically described as being negative feedback because it is protective
Figure 13.16 Components of a Reflex Arc
Reflex classification
According to
development
Site of information processing
Nature of resulting motor response
Complexity of neural circuit
Figure 13.17 Methods of Classifying Reflexes
reflex classifications: innate
Result from connections that form between neurons during development
Acquired reflexes
Learned, and typically more complex
Acquired
Acquired reflexes
Learned, and typically more complex

More reflex classifications
Cranial reflexes
Reflexes processed in the brain
Spinal reflexes
Interconnections and processing events occur in the spinal cord
still more reflex classifications: somatic
Involuntary control of the muscular
Might need to be immediate, rapid response
Can also be voluntary
Non precise reflexes
Types:
Superficial reflexes are triggered on the skin
Stretch reflexes triggered by the elongation of a tendon
Also called myotactic reflexes
Visceral
Visceral reflexes (autonomic reflexes)
Control activities of other systems

and more reflex classifications
Monosynaptic reflex
Sensory neuron synapses directly on a motor neuron
Typical of a transmission of a chemical response
Common also for stretch reflex
No interneuron involved
Polysynaptic reflex
Composition:
At least one interneuron between sensory afferent and motor efferent
Longer delay between stimulus and response depending on how many synaptic junction made
Produce more complicated response
Control several muscle groups
Figure 13.18 Neural Organization and Simple Reflexes
SECTION 13-5 Spinal Reflexes
Types
They have a large range of types:
Some are monosynaptic reflexes involving a single segment of the spinal cord
Other involve the many segments
The most complicated type is described as being intersegmental reflex arcs
Spinal Reflexes
Range from simple monosynaptic to complex polysynaptic and intersegmental
Many segments interact to form complex response
Monosynaptic Reflexes
Stretch reflex automatically monitors and regulates the skeletal muscle length and tone
Typical A type Fibers (move the fastest)

Figure 13.20 The Patellar Reflex
Patellar reflex
Patellar (knee jerk) reflex
Sensory receptors are muscle spindles that activated when they are stretched
This is the result of the tap on the patellar ligament’s special sensors which cause the stretch of muscle spindles of the quadriceps group
This causes a rapid increase in muscle tone
A rapid decrease in the sensory information then allows the muscle recover to less muscle tone
Figure 13.19 Components of the Stretch Reflex
What are muscle spindles?
These are the sensory receptors which are involved in the stretch reflex
There are two parts to each muscle spindle
Intrafusal muscle fibers
Extrafusal muscle fibers
These are responsible for maintaining muscle tone
Figure 13.21 Intrafusal Fibers
Intrafusal fibers
Innervated by both sensory and motor neurons
Dendrites of the sensory neuron surround the central portion of the intrafusal fibers
Axons from the spinal nerve form neuromuscular junctions at the end of this fiber
Innervated by motor neurons called gamma motor neurons and their axons are called gamma effectors
Polysynaptic reflexes
Produce more complicated responses
Can include those of ESPS and ISPA at CNS motor nuclei may include the inhibition or the stimulation
Tendon reflex
Withdrawal reflexes
Flexor reflex
Crossed extensor reflex
Tendon reflex
Since the stretch reflex monitors the length of the skeletal muscle
Then the tendon reflex monitors the external tension produced during a muscular contraction and prevents the tearing or breaking of the tendons
This requires sensory receptors which are distinct from those of the muscle spindles and the proprioceptors in the tendons
Thus as the tension increase on a skeletal muscle, increased inhibitory response occurs to prevent the tearing of the muscle

Withdrawal Reflexes
A reflex which moves an affected part of the body from the source of stimulation
Typically initiated by pain stimulation
Two types:
Flexor reflexes
Reciprocal inhibition
Cross Extensor Reflexes
Flexor reflex
Affects muscles of the limb
Respond to pain when you step on a tack
Here the sensory neurons affect interneurons which in turn affect the motor neurons
Reciprocal Inhibition
This means that when one set of muscles contract another set must relax
This means that when flexors contract, extensors relax
This response is more complicated than a monosynaptic response
If the stimuli is strong, many muscle groups can be affected
The effects are longer lasting the that of the patellar response
Crossed Extensor Reflexes
We know that the stretch, tendon, and withdrawal reflexes are called ipsilateral reflex arcs meaning that sensory and motor response occurs on the same side of the body
Those that occur on the opposite side of the body are called crossed extensor reflex arcs also known as contraleteral reflex arc
There are five types

Polysynaptic reflexes
Involve pools of interneurons
Are intersegmental in distribution
Involve reciprocal inhibition
Have reverberating circuits to prolong the motor response
Several reflexes may cooperate to produce a coordinated response
The five types of crossed extensor reflex
Those involving pools of interneurons
Intersegmental in distribution
Involve reciprocal inhibition
Reverberating circuits
Coordinated control response
Pools of interneurons
Processing occurs in pools of interneurons
The result might be excitation or inhibition of motor neurons
the flexor and crossed extensor reflexes direct specific muscle contractions
Segmental distribution
These interneuron pools are found in segmental groups and may activate muscle groups in many parts of the body
Affecting a plexus


An activity which coordinates muscle contractions and reduces resistance to movement
In the flexor and crossed extensor reflexes
Reverberating circuits
Positive feedback between interneurons that innervate motor neurons and the processing pool maintains the stimulation even after the stimulus has faded
Coordinated Control response
This is the ability to coordinate the response of activating one muscle group and inhibiting the other for an action to occur
Figure 13.22 The Flexor and Crossed Extensor Reflexes
SECTION 13-6 Integration and Control of Spinal Reflexes
Reflex behaviors can occur automatically

General
Reflex motor behaviors occur automatically without instructions from higher centers
However, descending tracts from higher centers acting through interneurons can inhibit of stimulate a reflex response
Voluntary movements and reflex patterns
We known that there are certain reflex patterns existing in the spinal cord
However, higher centers can control these as well
This means that fewer descending tracts are required for there control
and these provide the finer control
An important example is the biceps brachii muscle triceps brachii
Control of the spinal reflexes
Brain can facilitate or inhibit motor patterns based in spinal cord
Motor control involves a series of interacting levels
Monosynaptic reflexes are the lowest level
Brain centers that modulate or build on motor patterns are the highest
Reinforcement and inhibition
A single EPSP may depolarize the postsynaptic neuron sufficient to generate an action potential but can make the neuron more sensitive to other ESPS
ISPS will make make a postsynaptic neuron less sensitive to a response, this is a process of reenforcement
Reinforcement = facilitation that enhances spinal reflexes
Spinal reflexes can also be inhibited
Babinski reflex replaced by planter reflex in an adult
Babinski reflex: types
Positive: fanning of the toes in an infant
Negative: no fanning of toes in the adult
Figure 13.23 The Babinski Reflexes
You should now be familiar with:
The structure and functions of the spinal cord.
The three meningeal layers that surround the CNS.
The major components of a spinal nerve and their distribution in relation to their regions of innervation.
The significance of neuronal pools.
The steps in a neural reflex.
How reflexes interact to produce complicated behaviors.

Chapter 13, part 2
The Spinal Cord and Spinal Nerves
SECTION 13-3 Spinal Nerves
31 pairs of spinal nerves
Nerves consist three coverings in order:
Epineurium
Perineurium
Endoneurium
Epineurium
Outermost layer
Dense network of collagen fibers
Arteries of veins branch through the epineurium and branch within the perinerium
Perineurium
Middle layer
Divides the nerve into a series of compartments
Endoneurium
Inner most layer
Surrounds individual axons
Here capillaries which left the perineurium branch
Figure 13.8 A Peripheral Nerve
Peripheral Nerve Distribution of Spinal Nerves
A typical spinal nerve forms lateral to the intervertebral forms where the dorsal and ventral roots unite
Ventral root construction
Each root contains both sensory and motor neurons
Distally the first branch of the spinal nerve contains visceral motor fibers to a sympathetic ganglion
This branch has a light color and is called white an is called the white rami


Sympathetic nerves
These are postganglionic fibers that innervate smooth muscle, and organs in the thoracic cavity
Gray ramus
Unmyleinated fibers
They are responsible for innervating glands and smooth muscle in the body wall or limbs
Are unmyleinated
These rejoin the spinal nerve
Dorsal ramus
Motor and sensory fibers that innervate the skin and skeletal muscle of the back

Ventral rami
Supply the ventrolateral body surfaces on the body wall and the limbs

How communicate?
Dorsal, ventral, and white rami also contain sensory fibers
Somatic sensory information arrives over the dorsal and ventral rami
Visceral sensory information the dorsal root reaches the dorsal, ventral, and white rami
Spinal nerves in review
White ramus (myelinated axons)
Gray ramus (unmyelinated axons that innervate glands and smooth muscle)
Dorsal ramus (sensory and motor innervation to the skin and muscles of the back)
Ventral ramus (supplying ventrolateral body surface, body wall and limbs)
Each pair of nerves monitors one dermatome
Figure 13.9 Peripheral Distribution of Spinal Nerves
Figure 13.9 Peripheral Distribution of Spinal Nerves
What is a dermatome?
The region in which a specific region of the skin is monitored by the single pair of spinal nerves
Each pair of spinal nerves services its own dermatome
Good method of monitoring nervous system damage
Figure 13.10 Dermatomes
What is a nerve plexus?
Complex interwoven network of nerves
These are the result of separate ventral rami to provide sensory innervation and motor control to each part of a compound muscle
During development small skeletal muscle muscles innervated by different ventral rami fuse together to form large muscles with complex origins, but yet separate ventral rami continue to exists and to supply sensory and motor control to each part of the compd muscle
Remember that these spinal nerves form different rami blend together
Interwoven network of nerves

Nerve plexus
Complex interwoven network of nerves
Four large plexuses
Cervical plexus
Brachial plexus
Lumbar plexus
Sacral plexus
Cervical Plexus
Ventral rami of spinal nerves C1 through C5
Innervate muscles of the neck
The phrenic nerve is part of this which innervates the diaphram
Brachial Plexus
Innervates the pectoral girdle and the upper limbs
with contributions from the ventral rami of C5 – T 1
Originate from trunks or chords
Lumbar plexus
Arise from the lumbar segments
Innervate the pelvic girdle and lower limbs
T12 – L4


Sacral Plexus
L4 – S4
Sciatic nerve
Innervates lower portion of the foot
Motor performance
Automatic
Coordination within the cord
Reflexes
Stereotyped responses
No Conscious ability to control
Communication between the brain and spinal cord

Figure 13.11 Peripheral Nerves and Nerve Plexus
Figure 13.12 The Brachial Plexus
Figure 13.13 The Branchial Plexus
Figure 13.13 The Branchial Plexus
Figure 13.14 The Lumbar and Sacral Plexuses
Figure 13.14 The Lumbar and Sacral Plexuses

Chapter 13, part 1
The Spinal Cord and Spinal Nerves
Learning Objectives
Discuss the structure and functions of the spinal cord.
Describe the three meningeal layers that surround the CNS.
Describe the major components of a spinal nerve and relate their distribution to their regions of innervation.
Discuss the significance of neuronal pools.
Describe the steps in a neural reflex.
Explain how reflexes interact to produce complicated behaviors.
SECTION 13-1 General Organization of the Nervous System
Divisions of the Nervous System
CNS
Brain and spinal cord
In the white matter, axons arranged in tracts and columns
PNS
Remainder of nervous tissue
In the peripheral nervous system
Neuron cell bodies are located in the ganglia
Axons are bundled together in nerves with spinal nerves connecting to the spinal cord
Cranial nerves connect to the brain
In the central nervous system
A collection of neuron cell bodies with a common function is called a center
A center with a discrete boundary is a nucleus
The portions of the brain covered with thick gray matter is called the neural cortex
The term higher centers refers to the most complex integrations
The white matter
The write matter of the CNS contain bundles of axons which share common origins, destinations, and functions
These boundaries are called tracts
Tracts in the spinal cord are called boundaries
Centers and tracts
The centers and tracts which link the brain with the rest of the body are called pathways
Sensory pathways distribute information from the peripheral receptors to the processing centers in the brain
Motor pathways begin at the CNS centers concerned with motor control and end at the effectors which they control
Figure 13.1 An Introduction to the Anatomical Organization of the Nervous System
SECTION 13-2 Gross Anatomy of the Spinal Cord
Gross anatomy continued
The adult spinal cord is about 18 inches in length
The cord ends between L1 and L2
Posterior surface has a shallow grove called the posterior median fissure
The anterior median fissure is the deep grove on the anterior surface
Gray matter location
The amount of gray matter is the greatest in the segments of the spinal cord which deal with sensory and motor control of the limbs
Cervical enlargement: shoulder girdle and upper arms
Lumbar enlargement: pelvis and lower limbs

Spinal segments
Each spinal segment is associated with a pair of dorsal dorsal root ganglia
These ganglia contain the cell bodies of sensory neurons
The axons of these cell bodies form the dorsal roots
They bring sensor information to the spinal cord
Ventral roots
Contain the axons of motor neurons that extend into the periphery
Control somatic and visceral effectors

Spinal nerves
Distal to each dorsal root ganglia, the sensory and motor roots are bound together to create a mixed nerve
That is they contain both afferent and efferent fibers
Adult spinal cord
Localized enlargements provide intervention to limbs
31 segments
each segment has a pair of dorsal roots and a pair of ventral roots
Filum terminale
Conus medularis
Spinal nerves extend off cord to form mixed nerves
Mixed nerves
How locate
Each identified by their association with a adjacent vertebrae
This is a regional number
T1 means that the spinal nerve emerges immediately inferior to vertebra T1
Cervical nerve designation
The name comes from the vertebra immediately proceeding it
This means that there are 8 cervical nerves
Figure 13.3 Gross Anatomy of the Adult Spinal Cord
Spinal meninges
Provide physical stability and shock absorption, blood vessels branching within these layers deliver oxygen and nutrients to the spinal cord, Three divisions
Three layers
Dura mater
Arachnoid
Pia mater
Dura mater
Outer most layer which covers
Composed of dense collagen fibers that are oriented along the longitudinal axis of the cord
Tapers to coccygeal ligament
Epidural space separates dura mater from walls of vertebral canal and is lined with loose connective tissue, blood vessels, and adipose tissue
Figure 13.4 The Spinal Cord and Spinal Meninges
Figure 13.4 The Spinal Cord and Spinal Meninges
Arachnoid
Interior to dura mater are the subdural space, the arachnoid and the subarachnoid space
There might not be in real life a subdural space
Subarachnoid space contains CSF which acts as a medium for the diffusion of dissolved gases, nutrients, chemical messengers, and waste products
Extends inferiorly as far as the fiilum terminale and the dorsal and ventral roots of the cauda equina
Pia mater
Meshwork of elastin and collagen fibers that are firmly bound to the underlying neural tissue
Connective tissue holds the arachnoid and the pia matter together
Innermost meningeal layer
Denticulate ligaments extend from pia mater to dura mater to hold the layers together
There are also dual connections at the foramen magnum and the coccygeal ligaments prevent up and down motion
The meningeal membranes are continuous with the connective tissue that surrounds the spinal nerves and the peripheral branches
Figure 13.6 The Cervical Spinal Cord
Sections through the spinal cord
The spinal cord has what is called sectional organization
The anterior and posterior fissures mark the divisions between the left and right side of the spinal cord
The superficial white matter contains large numbers of of myleinated and unmyleinated axons
Gray matter is dominated by cell bodies of neurons, neurogilia, and unmyleinated axons
Sectional anatomy of the spinal cord
White matter is myelinated and unmyelinated axons
Gray matter is cell bodies, unmyelinated axons and neuroglia
Projections of gray matter toward outer surface of cord are horns
Figure 13.7 The Sectional Organization of the Spinal Cord
Figure 13.7 The Sectional Organization of the Spinal Cord
Organization of Gray matter
Cell bodies of the neurons in the gray matter are organized into functional nuclei
Here sensory nuclei relay information from the peripheral nerves
Motor nuclei issue commands to the peripheral effectors
Describing
In section we see that motor and sensory sections are separated from each other
Horns of spinal cord
Posterior gray horn contains somatic and visceral sensory nuclei
Anterior gray horns deal with somatic motor control
Lateral gray horns contain visceral motor neurons
Gray commissures contain axons that cross from one side of the cord to the other
The key is that the different regions have specific motor and sensory nuclei
Organization of White matter
Divided into six columns (funiculi) containing tracts
Ascending tracts relay information from the spinal cord to the brain
Descending tracts carry information from the brain to the spinal cord
Divisions of the white matter
There are three regions of white matter on each side of the column
Posterior white: posterior gray horn and posterior median sulcus
Anterior white: between the anterior gray horns and the anterior median fissure
Lateral white: between the anterior and posterior columns
Responsibility
Each column contains a tract
A bundle of axons in the CNS that uniform in appearance
Relay the same type of information in the same direction
Divided in two types:
Ascending
descending

Ascending tracts
Carry sensory information toward the brain
Descending tracts
Carry information away from the brain
Convey motor commands

Nerve impulse
These are electrical activities
Action potential travels along an axon
Information passes from presynaptic neuron to postsynaptic cell in order to be effective
Need not be another neuron
General properties of synapses: Electrical
found in the CNS and PNS
Rare
Pre- and postsynaptic cells are bound by interlocking membrane proteins linked together called connexons
Create protein pores to allow ions to move back and forth
Occur in the:
Vestibular nuclei of the brain
Eye
Ciliary ganglia
General properties of synapses: chemical
More common
Excitatory neurotransmitters cause depolarization and promote action potential generation
Inhibitory neurotransmitters cause hyperpolarization and
suppress action potentials
Chemical synapses
An arriving action potential may or may not trigger a response
Communication may occurs in only one direction

Classification of neurotransmitters
Excitatory
Inhibitory
However may not be exclusive
ACH is both
Cholinergic synapses
Release acetylcholine (ACh)
Information flows across synaptic cleft
Synaptic delay occurs as calcium influx and neurotransmitter release take appreciable amounts of time
ACh broken down
Choline reabsorbed by presynaptic neurons and recycled
Synaptic fatigue occurs when stores of ACh are exhausted
Synaptic delay
The time between the arrival of the neurotransmitter and the effect on the postsynaptic membrane
The diffusion time is a small part of the entire process
Most of it is due to the calcium influx and the neurotransmitter release time

Synaptic fatigue
Under conditions of constant stimulation, the recovery time to make more ACH is delayed
When the levels of ACH are restored then, communication can occur once again

Figure 12.19 The Function of a Cholinergic Synapse
Figure 12.19 The Function of a Cholinergic Synapse
Other neurotransmitters
Adrenergic synapses release norepinephrine (NE)
Other important neurotransmitters include
Dopamine
Serotonin
GABA (gamma aminobutyric acid)
Dopamine
CNS neurotransmitter
Lack of may cause Parkinson’s disease


Serotonin
CNS
Lack of may cause depression

Gamma aminobutyric acid
Reduce the effects of anxiety

Neuromodulators
Influence post-synaptic cells response to neurotransmitter
Neurotransmitters can have direct or indirect effect on membrane potential
Can exert influence via lipid-soluble gases
Figure 12.21 Neurotransmitter Functions
Figure 12.21 Neurotransmitter Functions
Figure 12.21 Neurotransmitter Functions
Neuromodulators
Compds that have a direct effect on membrane potential
Compds that have an indirect effect on membrane potential
Lipid soluble gases that exert their effects inside of the cell

Direct effect
Open and close ion channels
ACH
ionotropic

Indirect effect
Work through secondary messengers
metabotropic

Lipid soluble gases
NO
CO
Work through secondary messengers
Neuromodulators
These alter the response by changing the presynaptic neuron or the postsynaptuc neurons response to the neurotransmitter
Typically protein in nature
Properties of neuromodulators
Long term effects which are slow to appear
Trigger responses that involve intermediary compds
May affect both pre and post neurons
Can be release alone or in concert with neurotransmitters
Sometimes a neurotransmitter can be a neuromoedulator at a different receptor site
Opioids
Endorphins: similar to opium effects
Enkephalins:
Endomorphins
dynorphins
SECTION 12-6 Information Processing
Information processing
Simplest level of information processing occurs at the cellular level
Excitatory and inhibitory potentials are integrated through interactions between postsynaptic potentials
Excitatory postsynaptic potential
Graded depolarization
Result of the opening and closing of chemically regulated membrane channels


Inhibitory postsynaptic potential
Graded hperpolarization
Works on chemically channels

Postsynaptic potentials
EPSP (excitatory postsynaptic potential) = depolarization
EPSP can combine through summation: two types
Temporal summation
Spatial summation
IPSP (inhibitory postsynaptic potential) = hyperpolarization
Most important determinants of neural activity are EPSP / IPSP interactions ratios
Figure 12.22 Temporal and Spatial Summation
Figure 12.22 Temporal and Spatial Summation
Figure 12.23 EPSP – IPSP Interactions
Presynaptic inhibition
GABA release at axoaxonal synapse inhibits opening calcium channels in synaptic knob
Reduces amount of neurotransmitter released when action potential arrives
Temporal summation
Additional stimuli arriving
Occurs in rapid success
This means that more chemically regulated channels open from this stimuli
The degree of depolarization then increases

Spatial summation
Multiple stimuli arrive and enhance the effect
The effects are cumulative
Figure 12.24 Presynaptic Inhibition and Facilitation
Presynaptic facilitation
Activity at axoaxonal synapse increases amount of neurotransmitter released when action potential arrives due to the lowering of the action potential required
Enhances and prolongs the effect of the neurotransmitter
Figure 12.24 Presynaptic Inhibition and Facilitation
Rate of generation of action potentials
Neurotransmitters are either excitatory or inhibitory
Effect on initial membrane segment reflects an integration of all activity at that time
Neuromodulators alter the rate of release of neurotransmitters
Rate of generation of action potentials
Can be facilitated or inhibited by other extracellular chemicals
Effect of presynaptic neuron may be altered by other neurons
Degree of depolarization determines frequency of action potential generation
You should now be familiar with:
The two major divisions of the nervous system and their characteristics.
The structures/ functions of a typical neuron.
The location and function of neuroglia.
How resting potential is created and maintained.
You should now be familiar with:
The events in the generation and propagation of an action potential.
The structure / function of a synapse.
The major types of neurotransmitters and neuromodulators.
The processing of information in neural tissue.

Learning Objectives
Describe the two major divisions of the nervous system and their characteristics.
Identify the structures/functions of a typical neuron.
Describe the location and function of neuroglia.
Explain how resting potential is created and maintained.
Describe the events in the generation and propagation of an action potential.
Learning Objectives
Define the structure/function of a synapse.
List the major types of neurotransmitters and neuromodulators.
Explain the processing of information in neural tissue.
SECTION 12-1 An Overview of the Nervous System
nervous system overview
Nervous system
Provides swift, brief responses to stimuli
Endocrine system
Adjusts metabolic operations and directs long-term changes
Nervous system includes
All the neural tissue of the body
Basic unit = neuron
Divisions of the Nervous system
CNS (Central Nervous system)
Brain and spinal cord
PNS (Peripheral Nervous system)
Neural tissue outside CNS
Afferent division brings sensory information from receptors
Efferent division carries motor commands to effectors
Efferent division includes somatic nervous system and autonomic nervous system
Somatic Nervous system
Controls skeletal muscle
Most causes is under voluntary control
In the case of a reflex, is not under conscious control
Autonomic nervous system
Called visceral motor system
Provides automatic regulation of smooth, cardiac muscle and grandular secretions at the subconscious level
ANS includes the sympathetic and parasymapthetic divisions
These are antagonist to each other
Figure 12.1 Functional Overview of the Nervous System
SECTION 12-2 Neurons
Neuron structure
Perikaryon
Neurofilaments, neurotubules, neurofibrils
Axon hillock
Soma; cell body
Axon
Collaterals with telodendria
Figure 12.2 The Anatomy of a Multipolar Neuron
Synapse
Site of intercellular communication
Neurotransmitters released from synaptic knob of presynaptic neuron
Figure 12.3 The Structure of a Typical Synpase
Neuron classification
Anatomical
Anaxonic
Unipolar
Bipolar
Multipolar
Anaxonic
Small and have no features which distinguish axons from dendrites
Located in the brain and organs of special sense
Bipolar Neurons
Two process, one axon and one dendrite
Occur in organs of special sense
Unipolar neurons
Dendrites and axons are continuous
Most sensory neurons of the PNS
Multipolar Neurons
Two of more dendrites
Single axon
Typically motor neurons
Figure 12.4 A Structural Classification of Neurons
Functional
Sensory neurons
deliver information from exteroceptors, interoceptors, or proprioceptors
Motor neurons
Form the efferent division of the PNS
Interneurons (association neurons)
Located entirely within the CNS
Distribute sensory input and coordinate motor output
Exteroceptors
Provide information about the external environment in the form of:
Touch
Temperature
Pressure sensations
Smell
Sight
Hearing
Proprioceptors
Monitors the position and movement of the skeletal muscle
Interoceptors
Monitors the digestive, respiratory, cardiovascular, urinary, and reproductive systems and provides sensations taste, deep pressure, and pain
Motor neurons
Efferent neurons
Efferent division of the PNS
Carry information away from the CNS to an peripheral effector in a peripheral tissue
Two types of motor neurons
Somatic motor neurons
Visceral motor neurons
Somatic Motor Neurons
SNS = somatic nervous system
Innervates skeletal muscle
Visceral Motor Neuron
ANS
Innervates smooth and cardiac muscle, glands, and adipose tissue
The order of connection:
Preganglionic fibers
Autonomic ganglia
Post ganglia fibers
Interneurons
Figure 12.5 A Functional Classification of Neurons
SECTION 12-3 Neuroglia
Neuroglia of the Central Nervous System
Four types of neuroglia in the CNS
Ependymal cells
Related to cerebrospinal fluid
Astrocytes
Largest and most numerous
Oligodendrocytes
Myelination of CNS axons
Microglia
Phagocytic cells
Interneurons
Association
Found in brain and spinal cord
Responsible for the distribution of sensory information
Also responsible for the distribution of motor activity
Figure 12.6 An Introduction to Neuroglia
Figure 12.7 Neuroglia in the CNS
Figure 12.7 Neuroglia in the CNS
Organization
The organization of the CMS differs from the PNS because of the greater number of distinctive cell types
Ependymal cells
The ventricles and the central canal are lined with these cells
They are responsible for the production of CSF
Typically cuboidal to columnar in shape
These are cilia covered cells which helps the CSF move through the ventricles and the central canal
Astrocytes
Largest and most numerous of the cell types
Jobs functions:
Maintaining the blood brain barrier
Create a network for the CNS
Repair damaged neural tissue
Guiding neuron development
Controlling the interstital environment
Maintaining the Blood brain barrier
The neurons must be isolated from the changes that occur in the blood
These cells isolate the neurons from the rest of circulation
They are designed to form a blanket around the blood capillaries
CNS Framework
The neuron network builds upon the Astrocytes
Repair of damaged nerve tissue
These cells help stabilize the tissue and prevents more damage
Guiding neuron development
Directs the growth and interconnections of neurons

Controlling the interstital environment
Adjusts the composition of interstital fluid
Regulates the concentration of potassium and sodium ions and carbon dioxide levels
Provide a means for the movement of ions and nutrients between the capillaries and the neurons
Absorb and recycle neurotransmitters
Release chemical which can enhance or suppress communication between the neurons
Oligodendrocytes
Smaller than and with fewer cell process than astrocytes
Responsible for wrapping around an axon with concentric mylein layers
Often wraps around several axons
Allows neuronal tissue to appear white in color
Unmyleinated nerve tissue is gray in color
Microglia
Smallest and least numerous of the cells of the CNS
Migrate through neural tissue
Wandering police force
Neuroglia of the Peripheral Nervous System
Two types of neuroglia in the PNS
Satellite cells
Surround neuron cell bodies within ganglia
Schwann cells
Ensheath axons in the PNS
Only one axon
However, many are required for that one axon