Nervous system & Brain parts, types, function, uses

NERVOUS SYSTEM AND BRAIN

The organ system comprising brain, spinal cord and nerve tissues is called nervous system. The nervous system is responsible for control and coordination of the body. In nervous system, the electric signals are generated in the form of nerve impulses which are usually associated with the fast response to the envision of mental stimuli. The nervous system performs following function.

• It helps to get information of change in environment through sense organs.

• It makes the body capable of conduct involuntary activities such as breathing, 

rhetoric, contraction and expansion of heart.

• It helps to regulate voluntary activities of the body i.e. movement of different parts of the body while doing work.

• It helps in remembering, thinking, reasoning, etc

Nervous system are basically divided into three divisions.

a. Central nervous system

b. Peripheral nervous system

c. Autonomic nervous system

Central Nervous system (CNS)

Central nervous system lies along the main longitudinal axis of the body. It consists of brain, spinal cord.

Brain

The largest and the topmost part of the central nervous system is called brain. It is situated in the cranial cavity of the skull. Human brain weighs about 1.2kg to 1.4kg. The brain is completely covered by three layered membrane called meninges. In meninges the outer most layer is called durameter. It is a thick layer attached to the inner side of cranium. The innermost layer is called piameter. It remain attached to the brain. The middle membrane is called arachnoid. The space between arachnoid and piameter is filled with special type of fluids. This fluid is called cerebospinal fluid. This fluid protects the brain from extreme injuries.

The brain is divided into three parts. They are cerebrum, cerebellum and medulla oblongata.

Cerebrum

It is the largest and most complexed art of the brain. It occupies about 80% of the brain. It is divided into two halves by a deep longitudinal cerebral fissures. Each half is called cerebral hemisphere. Each cerebral hemisphere is divided by three deep fissures into four loves: frontal lobe, parietal lobe, occipital lobe and temporal lobe

Each cerebral hemisphere is hollow internally and it's wall consists of an outer and inner part. The outer part consists of cell bodies of neuron and grey in colour. It is called grey matter. It is found folded in the form of ridge and furrows. It is believed that higher number of fold in the brain represent the greater intelligence. Thrist, pain, stress, anger, mood and conduction of forecast. It also controls the function of other parts of the brain. A person goes to comma, if cerebrum stops working.

Cerebellum

Cerebellum is also called small brain. It is the second largest part of the brain. There are two lemon sized semicircular structures lying below the posterior part of the cerebrum and above the medulla oblongata. Like cerebrum it's outer surface is formed by grey matter and inner core is formed by white matter. It does the following functions.

• Maintain the balance and equilibrium of the body.

• It conducts the voluntary movements. It makes the body movement smooth, steady as well as coordinated.

• It maintains the muscular tone.

Medulla oblongata

It is the posterior part of the brain. It is cylindrical in shape and lies near the cerebellum. The spinal cord arise from the lower part of the medulla oblongata. It is also made up of grey matter and white matter. Any injuries in the medulla oblongata causes spontaneous death of a person. Medulla oblongata performs the following functions.

• It controls respiration and swallowing of food, vomiting, sneezing and coughing.

• It controls heart beat.

• It also controls the expansion and contraction of blood vessels.

• It controls salivation action of alimentry canal, involuntary movement, secretion of digestive jucies as well as hormones.

• It receives and integrates the signals from spinal cord and sends it to the cerebrum and cerebellum.

Spinal cord

A long nerve tissues lying inside the neural canal of vertebral column is called spinal cord. It originates from the lower part of the media oblongata and extends up to first lumbar vertebrate. It is about 45cm in length and 2cm in thickness. It also consists of grey matter and white matter. In spinal cord grey matter remains inside and white matter remains outside. Any injuries and shock in spinal cord cause paralysis of the body parts below the point of the injury. It is also surrounded by meninges and protected by cerebospinal fluid. There are 31 pairs of nerve originating from spinal cord. The spinal cord does the following functions.

• It conducts sensory and motor impulses to and from the brain.

• It acts as the centre of reflex action.

Reflex action

We come across different experiences which occurs unconsiously and involuntarily. If we touch hot body suddenly, we withdraw our hands immediately. Similarly blinking of eyes occurs unconsiously when foreign particle comes near to our eyes, hands support our body automatically when we fall suddenly, mouth water on seeing food. All these actions which occurs immediately and involuntarily are the examples of reflex action. An immediate and involuntary action of the body in response to certain stimulus is called reflex action. During reflex action nerve impulses travels along the path way of sensory and motor nerve. This pathway is called reflex arc.

Major components of reflex arc are as follows:-

Sensory (receptor) organ :- It receives the stimulus.

Sensory (afferent) nerve :- It transmits the impulse from the receptors organs to spinal cord.

Connector neuron :- It carries impulses from upper part of the spinal cord to the lower part.

Motor (efferent) nerve :- It carries message from the spinal cord to the effector organ.