Inside:

CNS and its

parts

PNS and its

parts

Three Meninges

The meninges is the system of membranes which envelops the central nervous system. In mammals, the

meninges consist of three layers: the dura mater, the arachnoid mater, and the pia mater. The primary

function of the meninges and of the cerebrospinal fluid is to protect the central nervous system.

Dura mater

The dura mater [Latin: 'tough mother'] (also rarely called meninx fibrosa or pachymeninx) is a thick,

durable membrane, closest to the skull. It consists of two layers, the periosteal layer which lies closest to

the calvaria (skull), and the inner meningeal layer which lies closer to the brain. It contains larger blood

vessels which split into the capillaries in the pia mater. It is composed of dense fibrous tissue, and its

inner surface is covered by flattened cells like those present on the surfaces of the pia mater and

arachnoid. The dura mater is a sac which envelops the arachnoid and has been modified to serve several

functions. The dura mater surrounds and supports the large venous channels (dural sinuses) carrying

blood from the brain toward the heart.

The dura has four areas of infolding which include :

Falx cerebri, the largest, sickle-shaped; separates the cerebral hemispheres. Starts from the frontal crest

of frontal bone and the crista galli running to the internal occipital protuberance.

Tentorium cerebelli, the second largest, crescent-shaped; separates the occipital lobes from cerebellum.

The falx cerebri attaches to it giving a tentlike appearance.

Falx cerebelli, vertical infolding; lies inferior to the tentorium cerebelli, separating the cerebellar

hemispheres.

Diaphragma sellae, smallest infolding; covers the pituitary gland and sella turcica.

[edit]Arachnoid mater

The middle element of the meninges is the arachnoid mater, so named because of its spider web-like

appearance. It provides a cushioning effect for the central nervous system. The arachnoid mater is a

thin, transparent membrane. It is composed of fibrous tissue and, like the pia mater, is covered by flat

cells also thought to be impermeable to fluid. The arachnoid does not follow the convolutions of the

surface of the brain and so looks like a loosely fitting sac. In the region of the brain, particularly, a large

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number of fine filaments called arachnoid trabeculae pass from the arachnoid through the subarachnoid

space to blend with the tissue of the pia mater.

The arachnoid and pia mater are sometimes together called the leptomeninges.

Pia mater

The pia mater [Latin: 'soft mother'] is a very delicate membrane. It is the meningeal envelope which

firmly adheres to the surface of the brain and spinal cord, following the brain's minor contours (gyri and

sulci). It is a very thin membrane composed of fibrous tissue covered on its outer surface by a sheet of

flat cells thought to be impermeable to fluid. The pia mater is pierced by blood vessels which travel to

the brain and spinal cord, and its capillaries are responsible for nourishing the brain.

Spaces

The subarachnoid space is the space which normally exists between the arachnoid and the pia mater,

which is filled with cerebrospinal fluid.

Normally, the dura mater is attached to the skull, or to the bones of the vertebral canal in the spinal

cord. The arachnoid is attached to the dura mater, while the pia mater is attached to the central nervous

system tissue. When the dura mater and the arachnoid separate through injury or illness, the space

between them is the subdural space.

meninges /me·nin·ges/ (mĕn-in´jēz) sing. meninx [Gr.] the three membranes covering the brain and

spinal cord: dura mater, arachnoid, and pia mater.menin´geal

Spinal cord

The spinal cord in the simplest part of the central nervous system and is connected to the brain by the

delicate brain stem and contained within the spinal cavity. It is an oval shaped cylinder that tapers

slightly as it descends with two bulges as labeled in the diagram. The spinal cord mediates simple

reflexes and is extremely delicate and important. It provides conduction paths to and from the brain

called ascending tracts and descending tracts. The sensory impulses go up towards the brain and the

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motor impulses come back down. It also is the reflex center for all spinal reflexes. IT switches impulses

from afferent to efferent neurons. ©8

Nerve roots

There are 31 spinal nerves connected to the spinal cord, numbered by the level they emerge from the

spinal cavity. These attach by 2 types of short roots, a ventral nerve root or a dorsal nerve root. Vertral is

anterior and dorsal is posterior. The dorsal is easily recognized by the spinal ganglion. The ventral roots

carry motor neurons to effectors, also known as muscles and glands. The dorsal root carry information

from receptors in the peripheral nerves. ©8

Function of the Brainstem: It performs sensory, motor, and reflex functions. The spinothalamic tracts that pass through the brain stem are on the way to the thalamus. Nuclei in the medulla have reflex centers like cardiac, vasomotor, and respiratory. Other centers in the medulla are responsible for nonvital refluxes such as vomiting. The pons contains centers for reflexes mediated by the 5th, 6th, 7th, and 8th cranial nerves. Finally, the midbrain also contains reflex centers for certain cranial nerves such as eye movements mediated by the 4th cranial nerve.

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Functions and Structure of the Cerebellum

Function: The cerebellum performs three general functions. It acts with the cerebral

cortex to produce movements by coordinating the groups of muscles. It helps control

posture by functioning below the level of consciousness to ensure smooth and steady

movements. It also controls skeletal muscles to maintain balance.

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Structure and Function of the Diencephalon

Function: The functions of the thalamus are the part it plays in the mechanism responsible for sensations. Impulses from receptors upon reaching the thalamus produce conscious recognition of the sensations. It plays a part in the mechanism responsible for emotions by associating sensory impulses with feelings. It plays a part in the alerting mechanism, and the mechanism that produces complex reflex movements. The functions of the hypothalamus are that it functions as a high autonomic center and as a relay station between the cortex and the lower autonomic centers. It synthesizes hormones, performs endocrine functions, essential role in maintaining the waking state, appetite mechanism, and part of the mechanism responsible for maintain body temperature.

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Cerebral Cortex Structure and Function

Functions: Functions of the cerebral cortex include: sensory functions being somatic or “general senses”, motor functions such as movement of individual muscles, and integrative functions such as consciousness, language, emotions, and memory. All the parts of the cerebral cortex work together and individually to help with the mechanisms that control many parts of the body.

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The somatic nervous pathway is made up of nerves that connect to the skin, sensory organs and all

skeletal muscles. The system is responsible for nearly all voluntary muscle movements as well as for

processing sensory information that arrives through external stimuli, which are things like hearing, touch

and sight.

The somatic motor pathways include smooth muscle, cardiac muscle, and glands. The two divisions

would be sympathetic division and parasympathetic division.

Frontal lobe

Parietal lobe

Cerebellum

Thalamus Occipital lobe

Cerebrum

ain

Spinal

Cord

ain

Nerve

Root

ain

Cervical

Enlargement Cerebellum

Lumbar Enlargement

Membranous covering

(meninges)

Filum terminale

The Cerebral Cortex is described the “gray”

matter that covers the entire brain. The cerebral

has a very important function of responsible for

sensing and interpreting input from various sources

and maintaining cognitive function. Sensory

functions interpreted by the cerebral cortex include

hearing, touch, and vision. Cognitive functions

include thinking, perceiving, and understanding

language. For additional information on the

cerebral cortex visit the Cerebral Cortex and

Cerebral Cortex Lobes pages.

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Somatic Sensory and Motor Pathways

Somatic Sensory pathways send impulses to the cerebral

cortex for it to perform its sensory functions. Most impulses

sent to the cerebral cortex end up going through three levels

through three pools of sensory neurons primary, secondary,

and tertiary. Primary sensory neurons conduct from the

periphery to the central nervous system. Secondary sensory

neurons conduct from the cord or brainstem up to the

thalamus. Tertiary neurons conduct from the thalamus to the

postcentral gyrus which extend through the portion known as

the internal capsule to the cerebral cortex. Somatic Motor

pathways are there for the cerebral cortex to perform its

motor functions. Impulses are from the motor areas and are

sent to the skeletal muscles .

Pg. 414 & 417

Cervical Plexus

Lumbar Plexus

Sacral Plexus

Sensory to back of head, front

of neck, and upper part of

shoulder; motor to numerous

neck muscles

Sensory to anterior abdominal wall,

external genitalia; sensory to outer part

of thigh.

Motor to quadriceps, Sartorius, and

Iliacus muscles. Motor to adductor

muscles of the thigh and medial side

of lower leg. Motor to calf and leg

muscles (skin of calf and foot). Coccygeal Plexus

Sensory to lateral surface on leg, and

dorsal surface on foot. Motor to

muscles on the back of the thigh.

Motor to buttock muscles, sensory to

skin of buttocks, posterior surface of

thigh and leg.

Cervical plexus found deep

within the neck. Brachial

Plexus found deep within the

shoulder. Lumbar Plexus;

network of nerves located in

the Lumbar region of the back

near the psoas muscle. Fibers

from the fourth and fifth

lumbar nerves and the first

four sacral nerves form the

Sacral Plexus. (LUMBOSACRAL

PLEXUS) when together. Last

sacral nerve, along with a few

fibers from S4 joins with the

coccygeal nerve to form a

small coccygeal plexus. Nerves

innervate the floor of the

pelvic cavity.

Brain

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Pg. 418- 419 Dermatomes- “Each skin surface area supplied by sensory fibers of a given spinal nerve is

called a dermatome, name that means “skin section.” Image (4)

Pg. 421 Myotomes- “skeletal muscle or group of muscle’s that receives motor axons from a given spinal

nerve. “ Image (5)

Pg. 421

Trigeminal Nerve- sensations

of head and face, chewing

movements.

Glossopharyngeal Nerve-

Sensations of tongue,

swallowing movements, aid

in reflex control of blood

pressure.

Facial Nerve- facial

expressions, secretion of

saliva, and tears.

Brain Stem

Vestibulocochlear Nerve-

Balance or equilibrium

sense.

Olfactory Nerve- sense of

smell

Hypoglossal Nerve- tongue

movements

Vagus Nerve-

Sensations and

movements. Slows

heart, increases

peristalsis. Accessory Nerve – Shoulder

movements, turning movements of

head, movements of viscera, and

voice production.

Brain ©11

Function:

Carries information into the Central Nervous System

Afferent nerves in the Somatic Sensory system, feedback information detected by

receptors in skin, skeletal muscles and sense organs.

In the ANS feedback information regarding the autonomic control of the viscera.

Purpose:

Help us maintain homeostasis by sensing changes in internal and external environment

Afferent vs. Efferent

Above is a chart of the efferent and afferent and the difference between

them. ©7

Autonomic Nervous System

Function: Pathways in the ANS carry

information to the visceral effectors which are

the smooth muscles, cardiac muscles, and

glands. It powers itself without our conscious

knowledge. It has two efferent divisions

including the sympathetic and

parasympathetic division. They are made up

of autonomic nerves, ganglia, and plexuses.

The parasympathetic division is the “rest and

repair” division that uses acetylcholine it’s

transmitter to slow the heartbeat, promote

digestion etc. Parasympathetic stimulations

have different effects on effectors such as

constriction of bronchioles and contraction of

urinary bladder. The sympathetic division

opposes the parasympathetic impulses which

would for example, raise the heartbeat.

Sympathetic stimulations have effects like

dilation of bronchioles and relaxation of

urinary bladder. As a whole, the ANS

functions to regulate autonomic effectors to

maintain homeostasis. For example, X Vagus

goes to the heart and controls the heartbeat,

while the IX Glossopharyngeal goes to the

lungs and control respiratory actions.

Sympathetic and Parasympathetic Systems

Sympathetic divisions consist of neural pathways separate from the

parasympathetic pathways. Sympathetic impulses stimulate an effector while

parasympathetic impulses tend to inhibit it. Sympathetic division’s main purpose

is to serve as a responder to stressful/increased demanding situations and the

parasympathetic division’s main purpose is to serve as a non-emergency, routine

body maintenance function.

Sympathetic is like an ambulance Parasympathetic is like a doctor’s visit

(Responding to immediate emergencies) (Routine checkup)

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