The organ system in an animal that serves
to coordinate and control the functioning
of all other organ systems in the body is known as nervous system.
Nervous system works with the endocrine
system to communicate, integrate and coordinate the functions of various organs
and systems in our body and helps the body to respond to the external stimuli.
In humans, the nervous system has two main
divisions:
• The central nervous system (CNS)
• The peripheral nervous system (PNS)
The central nervous system consists of
brain and spinal cord. It is regarded as the ‘thinker’ or ‘information
processor’ in the body.
The peripheral
nervous system includes the sensory and motor nerves and connects the central
nervous system with the sense organs, muscles and glands of the body. The
peripheral nervous system is regarded as ‘actor’ or ‘performer’ in the body.
Nerve cell or neuron
A neuron is the
basic unit of nervous tissue. Our nervous system contains about 10 billion
nerve cells, which communicate with each other in a specific manner.
Structure of the neuron
Each neuron has
a central area called the cell body or cyton.
The cell body has a large central nucleus and cytoplasm. Several
short, thread like branches called dendrites arise from the cell body.
One branch arising out of the cell body is very long in comparison to others.
This branch is called axon or nerve fibre.
Axon may or may not be covered by a fatty sheath called myelin sheath.
This covering is missing at intervals. These gaps on the sheath are known as
nodes of Ranvier.
Types of neurons
i. Sensory
neurons, which transmit impulse from receptor (sense organ) to coordinator (brain
or spinal cord).
ii. Motor
neurons, which transmit impulse from modulator to effectors (muscle or glands).
iii.
Connecting neurons, which connect sensory
and motor neurons, found in the grey matter.
Nerves
Nerves are
thread like structures, which emerge from brain and spinal cord and branch out
to almost all parts of the body. The nerves are composed of axons or nerve
fibres bundled together like the strands of an electric cable
Kinds of nerves
There are three
kinds of nerves. These are:
i. Sensory
nerves: These nerves contain sensory fibres. Sensory nerves bring impulse from
sense organs to the brain or the spinal cord.
ii. Motor nerves:
These nerves contain motor fibres. Motor nerves carry impulse from brain or
spinal cord to the effector organ like muscle or glands.
iii. Mixed
nerves: These nerves contain both sensory and motor nerve fibres and perform a
mixed function.
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