Reported by: Micol Villaflor

This module is about the main mechanism

of the body that controls or regulates its

functions. It describes the complementary

of structure and function of man’s nervous

system, and explains how the body

receives stimuli and responds to them

within and beyond the control of his will.

The nervous system helps all the parts of

the body to communicate with each other.

It also reacts to changes both outside and

inside the body. The nervous system uses

both electrical and chemical means to

send and receive messages.

When animals get hungry, they are

directed to the food sources by the nervous

system. When they feel cold, they search

for warmth in caves. When danger is near,

they avoid it. All our movements, decisions,

and actions are provided by the nervous

system. It enables us to evaluate our

environment, process information and

control our motion. A perfect guide.

Even while we are sleeping, our nervous

system is very active. It monitors and

adjusts internal processes and checks the

outside world for dangers. Our heart never

stops but beats slower while we are at rest.

Man controls or regulates his body

processes in two ways: (a) through a

nervous system and in by means of

chemicals known as hormones.

This function of the nervous system may be

from these statements:

1.) We receive information about our

surroundings from the sense organs (or

receptors) by way of sensory nerves.

2.) We process that information in the brain and

spinal cord.

3.) We react or respond to that information

through a command from the brain or spinal

cord by way of motor nerves to the effectors.

The things in the environment that cause an

organism to react or respond are referred to as

stimuli (singular, stimulus).

A receptor is a cell or organ to perceives a

stimulus, while an effector is a cell or organ that

demonstrates the body’s response to whatever

incites to action.

The figure shows the two

main division of man’s

nervous system. These

are:

a. the central nervous

system (CNS)

consisting

of the brain and spinal

cord; and

b. the peripheral nervoussystem (PNS) consisting of nerves which arise from the brain (they are called cranial nerves) and from the spinal cord (they are called spinal nerves).

The nerves of the peripheral nervous system end at the muscles and organs of the body.

The relationships of the parts of man’s nervous system are shown in the figure. The sense organs detects the stimulus. Sensory nerves relay the information to the spinal cord and/or the brain where it is processed. The central nervous system then sends a command to the proper effector through a motor nerves.

The extraordinary amount of information that your body receives at any one time is flashed through your nervous system in the form of millions of messages. These messages bring news about what’s happening inside and outside your body –about the itch on your head, or the sad news you heard, or the odor of a fried chicken. Almost immediately, your nervous system tells other parts of your body what to do – scratch the itch, be saddened by the news, or eat the fried chicken.

While your body is doing any of these

activities, your nervous system is also busy

monitoring or checking your breathing,

blood pressure, body temperature and

other body processes.

The nervous system keeps your body

working properly despite the constant

changes taking place around you. These

changes are called stimuli.

Although some responses to stimuli are

involuntary (not under your control), such

as blinking your eyes and sneezing, many

responses of the nervous system are

voluntary (under your control). For

example, opening an umbrella because it

is raining (stimulus) is a voluntary action.

It is a conscious effort that involves the

feelings of the moment, the memory of

what happened the last time you stayed

out in the rain, and the ability to reason.

From the moment you were born, the

nervous system controls and interprets all

the activities going on within your body.

Without you nervous system, you could not

move, think, laugh, feel pain, or enjoy the

taste of a mango juice.

The nervous system is constantly alive with

activity. It buzzes with messages that run to

and from all parts of the body.

Two types of cells make up the nervous

system: (a) nerve cells, or neurons, for

transmitting messages from one part of the

body to another. Neurons are unique

because, unlike most other cells in the

body, such as the red blood cells which

are produced regularly, that body cannot

produce neurons through out our lives.

Just like money deposited in a bank, once

used up, we will not have anything to

withdraw. Once damaged, neurons cannot

be replaced. But do not worry because the

number of neurons that you are born with is

so large that you will have more than

enough to last your entire lifetime. and (b)

supporting cells for protecting and assisting

neurons (also known as neuroglia or glial

cells).

The figure shows a

simplified structure of a

neuron. It consists of (a) a

cell body which contains

the nucleus, cytoplasm,

and/or organelles. and

(b) two types of

projection called nerve

fibers –

(1) the shorter, thinner, more numerous and highly branched dendrites and (2) the longer and thicker axon with fewer branches. Dendrites relay signals towards the cell body. Axons, on the other hand, conduct signals away from the cell body, either to another neuron or to an effector.

Along the axon, the

myelin sheath is not

continuous. These gaps

are called nodes of

Ranvier.

Neurons differ in the direction of the

message and type of impulse they carry:

a. Sensory neurons carry impulses to the

brain or spinal cord.

b. Motor neurons carry impulses from the

brain or spinal cord to the muscles.

c. Associative neurons, or interneurons, at

the central nervous system integrate data

from the sensory neurons and then relay

commands to motor neurons.

Just as there are sensory and motor

neurons, there are also sensory and motor

nerves. Neurons appear in bunches; the

long fibers of a bunch of neurons bundled

together form a nerve.

A sensory nerve consists of the long fibers

of a bunch of sensory neurons, while a

motor nerve consists of the long fibers of a

bunch of motor neurons. A third kind,

called mixed nerve, is a bundle of the long

fibers of both sensory and motor neurons.

1. The nervous system receives and sends out information about activities within the bodyand monitors and responds to change in the environment or stimuli. They transform these stimuli into impulses which are in the form of electro-chemical changes in the membrane of the nerve fibers.

2. The nervous system is divided into central nervous system and peripheral nervous system. The central nervous system is composed of the brain and the spinal cord. The peripheral nervous system consists of the nerves that connect the brain and the spinal cord to various parts of the body.

3. The basic unit of structure and function of

the nervous system is the neuron, which is

made up of cell body, dendrites and axon.

4. The dendrites are the short, highly

branched projections that convey impulses

toward the cell body. The axon is the long

and less branched projections that convey

impulses away from the cell body.

5. A nerve impulse send messages in the

form of electrical and chemical signals.

6. The neuroglia or glial cells assist and

support the neuron in performing various

metabolic functions.

7. Neurons can be classified into three

types. These are:

Sensory neurons receive information and

send impulses to the spinal cord or brain.

Motor neurons conduct impulses from the

brain or spinal cord to muscles and glands

in the body.

Interneurons, nerve cells throughout the

brain and spinal cord, relay impulses from

sensory neurons to motor neurons.