Download NERVOUS SYSTEM IN HUMAN BEINGS

Class X
Episode 4
A P State
NERVOUS SYSTEM IN HUMAN BEINGS
You all must have seen a Computer and most of you also use the
computer. What are the parts in a computer? The C P U Monitor, Keyboard, and
the Mouse.
The C P U is the central processing unit. In it is the processor, hard disk
for storing data, RAM, ROM, Mother board etc. The C P U is the center of all
activity. Its parts are controlled and coordinated and without this function the
computer cannot function and cannot display anything on the monitor. Keyboard
typed the data to be fed in to the PC. Mouse is used for maneoverabity. But the
brain of computer is the C P U. It processes, analyses, stores, deletes data etc.
The human body which has many organs needs control and coordination.
No organ con function independent of the other. The basic fundamental
characteristic of living organisms is ability to respond to stimuli. In human being
this is achieved by the nervous system. Nervous system brings about rapid and
short lasting responses while endocrine system brings about slower and long
lasting responses.
The endocrine system is placed deep inside the body and cannot sense
and respond to changes that occur outside the body. Hence in the course of
evolution a second system the NERVOUS SYSTEM developed.
Nervous system can respond to changes both inside and out side the
body by specialized cells known as RECEPTORS.
The stimuli reach the nervous system as electrical currents. They are
analyzed and the response is transmitted to target tissue like glands and muscles
in the form of electric current.
A child touches a fire and removes its hands immediately. The nervous
system stores such responses for future use. The child shall always know not to
touch fire again.
Animate the Above
(1)
Child goes near fire
(2)
Touching it
(3)
Removing it
(4)
Not touching fire again and moving away.
What are the major functions of a nervous system?
a) To Control and Coordinate various body activities – both voluntary
and involuntary
b) To regulate internal environment of the body.
c) To react to the environment through sense organs.
What are the components of a Nervous System?
The nervous system in human beings has three parts
a) Brain
b) Spinal Cord
c) Nerves.
The brain is like the C P U of a computer where the stimuli are analyzed
and responses are decided.
The spinal cord receives the messages from body parts and
transmits to the brain. It sends the messages received from the brain to
body parts. It is like a telephone exchange.
The nerves are like the telephone wires which carry information to
and from the brain and spinal cord to different parts of the body.
Diagram
What is the fundamental Unit of a nervous System?
The fundamental unit of a nervous system is the nerve cell or
NEURON. Let us now examine the structure of a neuron.
3D Diagram
The Neuron has
a. cell body or cyton
b.dendrites
and an c) Axon
CYTON
Cyton is also known as PERIKARYA. A large nucleus is present in the
granular cytoplasm. Saome granules are specialized and contain RNA. These
granules are known as
Nissil’ s Granules. They are concerned with protein synthesis.
DENRITES:-
From the cyton arise short projections or processes known as
DENDRITES. The dendrites look like branches of a tree. They receive
information from other neurons and carry the information to cyton.
One of the projections of cyton is long and is known as AXON.
AXON:Axon conducts messages away from cyton. The length of axon may vary
from few millimeters to a meter. In brain the axon is short. It is long in some
regions of the body like the one from spinal cord to the toe.
Neuron in brain
A Neuron
The axon is covered by a multilayered sheath known as MYELIN
SHEATH. In regions where this sheath is absent the axon is called
Non myelinated axon. The region between segments of myelin is known as Node
of Ranvier. The Myelin sheath is useful to increase the speed of nerve impulse
conduction and prevents over lapping of messages in the neighboring nerves.
Nutrition to the neurons is provided by supporting cells known as Glial Cells.
At the end, axon gives out several branches which end in nerve endings.
The nerve endings make contact with the dendrites of another or axon of another
nerve cell.
The contact is not physical. There is a minute space between the nerve
ending and dendrite. This site termed as a SYNAPSE.
Animate Synapse
What is nerve impulse?
When a stimulus is applied to the neuron a small electrical potential of about
0.055 volts is generated. This potential is called ACTION POTENTIAL or Nerve
impulse.See the animation.
Action Potenital of a Nerve Impulse Animation.flv
In the next episode we shall examine the Human nervous system.
Animate nerve potential
Conduction of nerve impulse
How is the nerve impulse conducted?
The Conduction of nerve impulse from one neuron to another
neuron takes place at SYNAPSE.
An electrical impulse traveling down the axon releases molecules of the
neurotransmitter in this gap of synapse. These molecules cross the gap and
excite the activity of the second neuron. This neuron now fires an electrical
impulse along its own axon. This continues from one neuron to other neuron till
the electrical impulse reaches the spinal cord or brain or effector organ.
Thus synapse
1) Helps in passing information from one neuron to another
2) Helps the adjacent neurons to be excited or inhibited
3) Amplifies a signal
And 4) Ensures that nerve impulse travels in one direction only
How many types of neurons are there?
There are three types of neurons based on function and three types based on
structure.
Types of neurons based on Function
The three types of neurons based on function are
a) Sensory (Afferent)
b) Motor (Efferent)
c) Connector neurons.
The sensory neurons transmit messages from the receptor to the brain
and spinal cord.
The motor neurons transmit messages or instruction to effectors
i.e., organs which have to respond to the stimulus.
The connector neurons are mainly found in brain and spinal cord
connecting the neurons.
Types of neurons based on structure
The three types are
1) Unipolar neuron.
2) Bipolar neuron.
3) Multipolar neuron.
Unipolar neuron has a single very short process. Dendrites are absent.
Bipolar neuron has two processes the axon and dendrite.
In Multipolar neuron the Cyton is branched at many points, forming many poles.
How many types of nerves can be found in our body?
There are mainly three types of nerves.
1) Sensory Nerves carry information from the sense organs and receptors
to specific area of brain and spinal cord.
Ex: sensory nerves of eye, ear, nose, tongue, skin etc
2) Motor nerves carry impulses from the brain or spinal cord to effector
organs. Stimulation of motor nerves make the muscles contract
3) Mixed nerves has both sensory and moter nerve fibres.
The neurons in our body remain through out life. The do not divide. The cannot
be reproduced. This is the reason that in polio effected children the neurons are
destroyed in the affected parts specially the limbs. The damage is permanent can
cannot be revived
In this episode we have seen the importance and functions of the nervous
system. We have also learned the structure and function of a neuron, different
types of neurons, different types of nerves and the conduction of nerve impulse.
In the next episode we shall study the structure and functions of the three
parts of nervous system namely
1) Central nervous System.
2) Peripheral Nervous System.
and 3) Autonomous Nervous System.