650 words essay Nervous System for Medical students



The nervous system is the latest system evolved for the purpose of co-ordination, reception of external stimuli and response to them. The nervous system is composed of the brain and spinal cord and the nerves given off by these structures.

The brain and spinal cord form what is called the Central nervous system. Nerves which convey impress­ions from the special organs of senses like vision, hearing, taste and smell; and impressions from the skin, such as touch, pain temperature etc. are called afferent or sensory nerves. When these in coming impulses reach the central nervous system other nerves come into play.

For instance, if light is too strong, the eyes are immediately 'closed. These movements, in common with all voluntary movements are affected by the muscles of our body, and the nerves play an important part in these movements.

Such nerves' may be compared to a telegraphic system, by which sensa­tions such as pain, heat etc., are transmitted by the afferent nerves to the central organization in the brain which transmits its orders by the efferent or muter nerves to the muscles concerned and the required movements are carried out.

The brain and spinal cord consist of nerves and small bodies called centers or ganglion cells, and it is these cells which receive the different impressions. The spinal cord is about 18 inches long and 1/2 inch broad. It is composed partly of white and partly of grey looking matter, the white forming the outside portion and the grey the central portion of the cord.

The spinal cord gives off 32 pairs of nerves through openings on either side of the spine each nerve having two roots. When the spinal cord is injured the motor nerves may not be able to convey impressions to certain parts of the body.

Movements and other actions are n it then possible, and that part of the body is said to be realized. Reflex actions are those actions which are performed unconsciously or without the action of the will. Many of our actions are performed in this way.

Locomotion to a large extent and the movement of the lungs in respiration are examples of what is called automatic action. For instance once the impulse to walk is set up in the brain and the movement is started, it no lon­ger requires an effort of will to move the limbs The actions continues without conscious thought, it becomes, so to speak, automatic.

The Brain:

The brain is a very c6mplicated organ, and consists of very many different and important parts. It is divided into the cerebrum and cerebellum. The cerebrum is divided into two portions situated in either side of the skull cavity.

Beneath the cerebrum or great brain, and at the back of the skull is the cerebellum or small brain. The brain is composed of the same substances as the spinal cord, and gives off 12 pairs of nerves called cranial nerves, some of which are the nerves of the special senses.

Others are for regulating the movements of the muscles of the eyeball and tongue. Another and very important nerve, called the Pneumonia-gastric which consists of both sensory and motor fibers, supplies branches to the lungs, heart, food pipe, stomach, liver etc., to enable them to perform their proper functions.

The Sympathetic Nervous System:

The sympathetic nervous system is a connected chain of ganglia given off by the spinal nerves on either side of the spine. The organs in the belly and chest cavities receive branches from this system, It is the sympathetic system of nerves that supplies the walls of arteries and regulates the amount of blood contained in then.

It is the action of the sympathetic nerve which causes sudden flushing of the face. It also regulates the action of the stomach, heart and other organs of the abdomen and chest to a large extent and helps to maintain the heat of the body.