In human beings, different activities are taking place
simultaneously. They need to be co-ordinated efficiently and effectively. The
co-ordination of different bodily activities are controlled by two mechanisms,
namely – (a) nervous control and (b) chemical control. The components of the
human nervous system are brain and the nerves.
The human nerves system:
The nervous system can be divided into:
(i) the
central nervous system or CNS
(ii) the
peripheral nervous system or PNS and
(iii) the
autonomic nervous system or ANS
The central nervous system comprises of the brain and the
spinal cord and regulates all activities of the body. The peripheral nervous
system includes all the nerves. The nerves form a network and spread throughout
the body. They are instrumental in connecting all parts of the body to the
central nervous system. The autonomic nervous system comprises of all the
nerves present in the involuntary organs like heart, stomach, lungs, etc.
On the basis of
their function, the nerves are categorized as afferent and efferent nerves.
Afferent nerves carry impulses from the sensory organs to the brain. Efferent
nerves carry impulses from the brain to the sensory organs.
The nerves are composed of neurons and neurogila. The
neurons are specialized cells capable of creating and transmitting
electromechanical impulses. The neurogila are supportive cells which assist the
neurons in their function.
To determine
whether the object is hot or cold we usually touch them. How do we detect that
we are touching a hot or cold object?
All the information from our environment is picked up by the
specialized tips of dendrites of a neuron. It sets off a chemical reaction
producing an electrical impulse which travels from the dendrite to the cell
body and from there, though the axon(nerve fiber) to its end. At the end of the
first axon, the electrical impulse induces the release of some chemicals. These
chemical produced go across the small gap(synapse) of 2-20 nanometre (nm)
between the neurons and starts a similar electrical impulse in the dendrite of
the next neuron. This is the procedure by means of which the impulses travels
in the body from the neurons and are delivered to the muscle cells or glands.
When an action
or movement has to be brought about, the muscle tissue does the final job. The
muscle cells should move to enable work to be done. The movements at the
cellular level takes place when the cells change their shape, so that they
shorten. Muscle cells possess special kind of proteins which are capable of
bringing about change in their shape and make the cell capable to respond to
the nervous electrical impulses.
We can infer that the nervous tissue is composed of a highly
organized network of neurons capable of transferring information in the form of
electrical impulses from one part of the body to another.
In accordance
to their functions, the neurons are classified into three groups namely
–sensory neurons, motor neurons and association neurons. Sensory neurons
conduct impulses from the sense organs to the brain and spinal cord. Motor
neurons conduct impulses from the brain and spinal cord to the effector organs
like muscles and glands. Association neurons perform intergrative functions of
the nervous system.
