how is the nervous system designed to perform its function?
TRANSCRIPT
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.