You don't have to flee any longer

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Body’s Digest

The cerebral cortex is a thin layer of

gray matter made up of neuron dendrites

and cell bodies that compose the surface

of the cerebrum. Consists of 2 halves a

right and left half. It controls sensory,

motor, consciousness, language, emotions

and memory. (1) (393)

STRUCTUREANDFUNCTION

Somatic Sensory pathways in the CNS:

For the cerebral cortex to perform its

sensory functions, impulses must first

be conducted to the sensory pathways.

Sensory paths to the cerebral cortex

are crossed. There are three main pools

of sensory neurons there are primary,

secondary, tertiary. (1) (399)

Somatic motor pathways in the

CNS: For the cerebral cortex to per-

form its motor functions, impulses

are conducted from its motor areas

to skeletal muscles by somatic mo-

tor pathways. Consists of motor neu-

rons that conduct impulses from the

CNS to skeletal muscles.(1) (400)

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Make it work sista and fight!

With the Sensory and motor pathways you are now fully aware of your

brains messaging throughout nerve impulses and the power with in your-

self. You’re practically a superhero!

PeripheralNervousSys.

There are thirty-one pairs of spinal

nerves that are connected to the spi-

nal cord, although they don’t have

special names they are numbered ac-

cording to the level of the vertebral

column at which they emerge from

the spinal cavity. (1)

Structure of the Spinal Nerves:

The structure of the spinal nerves

is separated into two sections, which

are attached to the spinal cord in

terms of roots. These roots are the

ventral and dorsal. The dorsal root

of each spinal nerve is easily recog-

nized by a swelling called the dorsal

root ganglion, or spinal ganglion.

(1)

Plexuses:

The ventral rami of most spinal

nerves subdivide to form complex

networks called plexuses. There

are four major types of plexuses,

and they are the cervical plexus,

the brachial plexus, the lumbar

plexus and the sacral plexus. (1)

Cervical Plexus is found deep with-

in the neck, the parts supplied

with this are the sensory to the

back of the head, front of the neck,

and upper part of the shoulder; mo

PeripheralNervousSys.

tor to numerous neck muscles. (1)

Brachial Plexus is found deep

within the shoulder. Lumbar Plex-

us, which is formed by the inter-

mingling of fibers from first four

lumbar nerves. This network of

nerves is located in the lumbar

region of the back near the soas

muscle. Sacral Plexus are the fi-

bers from the fourth and fifth

lumbar nerves and the first four

sacral nerves. It lies in the pelvic

cavity on the anterior surface of

the piriformis muscle.

Dermatomes & Myotomes:

Dermatomes- regions of skin surface ar-

ea supplied by afferent (sensory) fibers of

a given spinal nerve. (1)

Myotomes- skeletal muscles supplied by

efferent (motor) fibers of a given spinal

nerve. (1)

Cranial Nerves:

There are twelve pairs of cranial nerves

that connect to the brain, mostly to the

brainstem. They are also made up of

bundles of axons, which are the mixed

cranial nerve where axons of sensory and

PeripheralNervousSys.

motor neurons. Sensory cranial

nerve- axons of sensory neu-

rons only. Motor cranial nerve-

mainly axons of motor neurons

and a small number of sensory

fibers (proprioceptors).

1) Olfactory Nerve

2) Optic Nerve

3) Oculomotor Nerve

4) Trochlear Nerve

5) Trigeminal Nerve

6) Abducens Nerve

7) Facial Nerve

8) Vestibulocochlear Nerve

9) Glossopharyngeal Nerve

10) Vagus Nerve

11) Accessory Nerve

12) Hypoglossal Nerve

Afferent & Efferent Nerves:

There are two functional divi-

sions of the peripheral nervous

system which are the afferent

(sensory) division and the effer-

ent (motor) division. The effer-

ent division is divided further

into the somatic motor nervous

system and the efferent portions

of the autonomic nervous sys-

tem. (1)

PeripheralNervousSys.

Autonomic Nervous System:

Structure: : : : each pathway is up

of autonomic nerves, ganglia,

and plexuses, which are made of

efferent autonomic neurons. All

autonomic neurons function in

the reflex arcs. Efferent auto-

nomic regulation ultimately de-

pends on the feedback from sen-

sory receptors. Relay of two ef-

ferent autonomic neurons con-

ducts information from central

nervous system to autonomic ef-

fectors:

1) Preganglionic neuron- conducts

impulses from the central nervous

system to an autonomic ganglion.

2) Postganglionic neuron- efferent

neuron with which a preganglion-

ic neuron synapses with autonom-

ic ganglion

Function: : : : the autonomic nervous sys-

tem functions to regulate visceral

effectors in ways that tend to main-

tain or quickly restore homeostasis.

Sympathetic and Parasympathetic

divisions are tonically active, often

exerting antagonistic influences on

visceral effectors.

PeripheralNervousSys.

Doubly innervated effectors con-

tinually receive both sympathet-

ic and parasympathetic impuls-

es, and the summation of the

two determine the controlling

effect.

Sympathetic Nervous System:

The purpose of the sympathetic

nervous system is that under

resting conditions, the sympa-

thetic division can act to main-

tain the normal functioning of

doubly innervated autonomic ef-

fectors. As a result the sympa-

thetic impulses function to

maintain normal tone of the smooth

muscle in blood vessel walls. The ma-

jor function of this system is that it

serves as an “emergency” system-

the “fight-or-flight” reaction. (1)

Parasympathetic Nervous System:

The purpose of the parasympathetic

nervous system is the dominant con-

troller of most autonomic effectors

most of the time. This includes Ace-

tylcholine which slows the heartbeat

and acts to promote digestion and

elimination. (1)

TheBrainstem

Three divisions of the brain

make up the brainstem, the me-

dulla oblongata, the pons, and

the midbrain. (1)

The medulla oblongata is the

part of the brain that attaches

to the spinal cord, it is about an

inch in length and is separated

from the pons above by a hori-

zontal groove. It is composed of

white matter (projection tracts)

and a network called the reticu-

lar formation. In this reticular

formation there are various nu-

clei, or clusters of neuron cell

bodies. (1)

The pons, like the medulla, is also

composed of white matter and retic-

ular formation. Fibers that run

transversely across the pons and

through the middle cerebellar pe-

duncles into the cerebellum make up

the external white matter of the

pons and give it its arching appear-

ance. (1)

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TheCerebellum

The midbrain lies below the

pons and above the cerebrum.

Both white matter and reticular

formation compose the mid-

brain. Extending divergently

through it are two ropelike

masses of white matter named

cerebral peduncles. Tracts in

the peduncles conduct impulses

between the midbrain and cere-

brum. (1)

The function of the brainstem

is similar to the spinal cord. It

performs sensory, motor and re-

flex functions

The cerebellum is the second larg-

est part of the brain. A transverse

fissure separates the cerebrum from

the cerebellum. The cerebellum is

full of white matter much like the

cerebrum, it also has sulci and gyri

along its surface. The cerebellum is

composed of two larger lateral

masses the cerebral hemisphere and

the Vermis. (1)

The internal white matter of the

cerebellum is composed of some

short and some long tracts. The

shorter tracts conduct impulses

from neuron cell bodies located in

TheCerebellum

the cerebellar cortex to neurons

whose dendrites and cell bodies

compose nuclei located in the

interior of the cerebellum. The

longer tracts conduct impulses

to and from the cerebellum. fi-

bers of the longer tracts con-

duct impulses to and from the

cerebellum. Fibers of the longer

tracts enter or leave the cere-

bellum by way of its three pairs

of peduncles, inferior cerebellar

peduncles, middle cerebellar pe-

duncles, and superior cerebellar

peduncles. An important pair of

cerebellar nuclei are the den-

-tate nuclei, one of which lies in each

hemisphere. Tracts connect these

nuclei with the thalamus and with

motor areas of cerebral cortex. By

means of these tracts cerebellar im-

pulses are able to influence the mo-

tor cortex and vice versa. (1)

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TheDiencephalon

The functions of the cerebel-

lum all have to do with the con-

trol of skeletal muscles. The

cerebellum acts with the cere-

bral cortex to produce skilled

movements by coordinating the

activities of groups of muscles.

The cerebellum also helps to

control posture and maintain

balance. (1)

The Diencephalon is made up of

several structures. The two

main structures are the thala-

mus and hypothalamus. (1)

The thalamus is a mass of gray

matter made up of many nuclei.;two

in which are the geniculate bodies,

located in the posterior region of

each lateral mass. The geniculate

bodies play a role in processing audi-

tory and visual input. Large numbers

of axons conduct impulses into the

thalamus from all parts of the brain.

These axons terminate the thalamic

nuclei, where they synapse with neu-

rons whose axons conduct impulses

out of the thalamus to all areas of

the cerebral cortex. Thus the thala-

mus is a relay station for sensory im-

pulses on their way to the cerebral

cortex. (1)

TheDiencephalon

The thalamus’ functions are

taking impulses from appropri-

ate receptors and produce a

conscious recognition of less

critical sensations of pain like

temperature and touch. Plays

part in emotions/ association,

the thalamus also plays a part

in arousal and producing com-

plex reflex movements. (1)

The hypothalamus consists of

several structures that are un-

der the thalamus. It is small

but extremely important., be-

cause it contributes to both sur-

vival and the enjoyment of life. It

functions as a link between the mind

and the body. And also links to the

nervous and endocrine system. The

hypothalamus serves as a regulator

and coordinator of autonomic activi-

ties and provides a crucial role in the

route by which emotions can express

themselves in changed bodily func-

tions. It also plays a vital role in wa-

ter balance, waking state, appetite,

and body temp. (1)

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TheMeninges

Three meninges: dura mater,

arachnoid membrane, pia mater (2)

Inflammation of meninges:

meningitis (2)

Dura mater: made of strong

white fibrous material, outside of brain (2)

Arachnoid membrane: delicate,

cob like membrane, lies between dura and pia mater(2)

Pia mater: transparent matter that adheres to the outer sur-face if the brain and spinal cord, contains blood vessels (2)

Function of CSF (cerebrospinal flu-

id)

• Provides supportive, protective cushion (2)

• Reservoir of circulating fluid, which is monitored by the brain to detect changes in internal environ-ment (2)

Found within subarachnoid space

around the brain, spinal cord & sur-

rounding cavities, and canals of the

brain and spine. (2)

Spinal cord

• Within spinal cavity and extends from the foramen magnum to the lower border of the first lumbar ver-

TheMeninges

-tebrae (2)

• Oval shaped cylinder that ta-pers slightly from above down-ward with bulges in cervical re-gion & lumbar region (2)

Nerve Roots

• Carry sensory and motor info into spinal canal (fibers of dor-sal nerve root and central nerve root) (2)