MAJOR COMPONENTS OF THE NERVOUS

SYSTEM

The nervous system is divided into two parts,

central nervous system (CNS)

peripheral nervous system (PNS)
.
The CNS is composed of the
brain,
the cerebellum,
brain stem,
the spinal cord,

whereas the PNS comprises

all the components outside the cranium and spinal cord.

Physiologically, the PNS is divided into the

somatic nervous system

autonomic nervous system (ANS).
Function of nervous system
The nervous system is a highly organized communication
system that serves the body.
Nerve cells within the nervous system
receive, transmit, analyze, and communicate information
to other areas throughout the body. For example, sensations
such as touch, proprioception, pain, and temperature are
transmitted from the periphery as electrochemical impulses to
the
CNS through sensory tracts. Once information is processed
within the brain, it is relayed as new electrochemical impulses
to peripheral structures through motor tracts. This transmission
process is responsible for an individual's ability to interact with
the environment.
Individuals are able to perceive sensory experiences,
to initiate movement, and to perform cognitive tasks as
a result of a functioning nervous system.
BRAIN
Brain
The brain consists of the cerebrum, which is divided into
two cerebral hemispheres (the right and the left), the cerebellum,
and the brain stem.
The surface of the cerebrum or
cerebral cortex is composed of depressions (sulci) and ridges
(gyri).
The outer surface of the cerebrum is composed of
gray matter and is estimated to be 1.3 to 4.5 mm thick,
whereas the inner surface is composed of white matter fiber
tracts . Therefore, information
is conveyed by the white matter and is processed and integrated
within the gray matter.
Supportive and Protective Structures
The brain is protected by a number of different structures
and substances to minimize the possibility of injury. First,
the brain is surrounded by a bony structure called the skull
or cranium.
The brain is also covered by three layers of
membranes called meninges, which provide additional protection.
The outermost layer is the dura mater. The area between the dura
mater and the skull
is known as the epiduralspace. The next or middle layer is the
arachnoid. The space between the dura and the arachnoid is
called the subdural space. The third protective layer is the pia
mater. This is the innermost layer and adheres to the brain
itself .The pia mater also contains the cerebral circulation.
The cranial meninges are continuous with the membranes that
cover and protect the spinal cord.
Cerebrospinal fluid bathes the brain and circulates within the
subarachnoid space.
Lobes of the Cerebrum
The cerebrum is divided into four lobes
-frontal,
parietal,
temporal, and
occipital
Frontal lobe

The frontal lobe is frequently referred to

as the primary motor cortex.
The frontal lobe is responsible
for voluntary control of complex motor activities.
In addition
to its motor responsibilities, the frontal lobe also
exhibits a strong influence over cognitive functions, including
judgment, attention, awareness, abstract thinking,
mood, and aggression.
The principal motor region responsible
for speech (Broca's area) is located within the frontal
lobe. In the left hemisphere, Broca's area plans movements of
the mouth to produce speech.
In the opposite hemisphere,
this same area is responsible for non verbal communication,
including gestures and adjustments of the individual's tone of
voice.
Parietal lobe
Parietal Lobe.
The parietal lobe is the primary sensory
cortex. Incoming sensory information is processed and
meaning is provided to stimuli within this lobe.
Much of our perceptual learning requires a functioning
parietal lobe. The parietal lobe also plays a role in short-term
memory functions.
Temporal Lobe
.

The temporal lobe is the primary auditory

cortex.
Wernicke's area of the temporal lobe allows an
individual to hear and comprehend spoken
language. , musical discrimination, and long-
term memory
capabilities are all functions of the temporal lobe.
.
Occipital lobe
The occipital lobe is the primary visual
cortex providing for the organization,
integration, and interpretation
of visual information. The eyes take in visual
information and then send it to the occipital
cortex for interpretation
Cerebellum

The cerebellum controls balance and complex muscular

movements. It is located below the occipital lobe of the
cerebrum and is posterior to the brain stem. It fills the posterior
fossa of the cranium. Like the cerebrum, it also consists
of two symmetric hemispheres. The cerebellum is
responsible for the integration, coordination, and execution of
multijoint movements. The cerebellum regulates the initiation,
timing, sequencing, and force generation of muscle
contractions.
It sequences the order of muscle firing when a
group of muscles work together to perform a movement
such as stepping or reaching. The cerebellum also assists
with balance and posture maintenance.
Brain Stem

The brain stem is located between the base of the cerebrum

and the spinal cord and is divided into three sections

Moving cephalocaudally, the three areas are the

midbrain,
pons, and
medulla.
Each of the different areas is
responsible for specific functions.
The midbrain connects the
diencephalon to the pons and acts as a relay station for tracts
passing between the cerebrum and the spinal cord or cerebellum.
The midbrain also houses reflex centers for visual,
auditory, and tactile responses.
 The pons contains bundles of
axons that travel between the cerebellum and the rest of
theCNS and functions with the medulla to regulate the
breathing rate.
It also contains reflex centers that assist with orientation of the
head in response to visual and auditory stimulation.
Cranial nerve nuclei can also be found within the
pons, specifically, cranial nerves V through VIII, which carry
motor and sensory information to and from the face.
medulla is an extension of the spinal cord and contains the
fiber tracts that run through the spinal cord. Motor and sensory
nuclei for the neck and mouth region are located within
the medulla, as well as the control centers for heart and
respiration
rates. Reflex centers for vomiting, sneezing, and
swallowing are also located within the medulla.
. The system maintains and adjusts an individual's level of
arousal, including sleep-wake cycles.it also necessary for certain
self-regulating, homeostatic
functions and is involved in the modulation of muscle
tone throughout the body.
Spinal Cord

The spinal cord has two primary functions:

coordination of motor information and movement patterns and
communicationof sensory information.
Additionally, the spinal cord provides
a means of communication between the brain and the
peripheral nerves. The spinal cord is a direct continuation of
the brain stem, specifically the medulla. The spinal cord is
housed within the vertebral column and extends approximately
to the level of the first lumbar vertebra.
The spinal cord has two enlargements, one that extends from the
third
Cervical c3 segment to the second thoracic T2 segment and
another that extends from the first lumbar L1 to the third sacral S3
segment.. At approximately the
L1 level, the spinal cord becomes a cone-shaped structure
called the conus medullaris. The conus medullaris is composed
of sacral spinal segments. Below this level, the spinal
cord becomes a mass of spinal nerve roots called the cauda
equina. The cauda equina consists of the nerve roots for
spinal nerves L2 through S5
Spinal cord

• Internal Anatomy.
• Like the brain, the spinal cord is composed of gray and white
matter.
The center of the spinal cord, the gray matter, is distinguished
by its H-shaped or butterfly-shaped pattern. The gray matter
contains cell bodies of motor and sensory neurons and
synapses.
The upper portion is known as the dorsal or posterior
horn and is responsible for transmitting sensory stimuli
.
The lower portion is referred to as the anterior or ventral horn
). It contains cell bodies of lower motor neurons,
and its primary function is to transmit motor impulses.
The lateral hom is present at the T1 to L2 levels and contains cell
bodies of preganglionic sympathetic neurons. It is responsible
for processing autonomic information.
. The periphery of the
spinal cord is composed of white matter. The white matter is
composed of sensory (ascending) and motor (descending)
fiber tracts.
A tract is a group of nerve fibers that are similar in
origin, destination, and function. These fiber tracts carry
impulses to and from various areas within the nervous system.
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