The central nervous system (CNS) consists on the brain and the spinal. It receives information on the various parts of the body, as well as the surroundings, through the nerves that connect all parts of the body. It processes the information and directs the body to act accordingly.

The brain acts as the major decision –maker, simultaneously controlling various kinds of activities by sorting out the enormous inflow of information. It also stores some of the information and discards the rest. The spinal cord acts mostly according to the instructions given by the brain. However, it sometimes takes quick action independently, as in the case of reflex action, which is discussed later.

The brain


The brain lies within the cranium, a set of bones commonly, known as the skull. It is covered by membranes called meninges, and cushioned against shocks by a fluid called cerebrospinal fluid. This is found between the meninges and the brain, as well as inside the brain.

The brain may be divided into three parts –the forebrain, midbrain and hindbrain.

The forebrain also called the cerebrum; this is the anterior part of the brain. The right and left cerebral hemispheres together form the largest part of the forebrain, or rather, of the entire brain. Shaped somewhat like kidneys, they are partially separated from each other by a deep groove. Their outer surface is full of folds, which increase brain. Shaped somewhat like kidneys, they are partially separated from each other by a deep groove. Their outer surface is full of folds, which increase the surface area and help accommodate the maximum number of nerve cells. The cerebral hemispheres are the centre of intelligence and are concerned with learning, memory, emotion and reasoning. They also coordinate our voluntary actives and make us feel sensations like pain and heat. They control speech and the sense of touch, smell, sight, hearing and taste.

The hypothalamus, a small area of the cerebrum, is linked to the pituitary gland. It controls the endocrine system. It also controls many emotional reactions like fear and anger.

The midbrain this small region connects the forebrain with the hindbrain and spinal cord. It also controls the eye adjustments we need to make in order to see.

The hindbrain this is the posterior of part of the brain and is located below the forebrain. It consists of the cerebellum and the medulla oblongata. The cerebellum coordinates our movements, both voluntary and involuntary. It maintains the body’s posture and balance. The medulla oblongata, also called the brain stem, connects the brain to the spinal cord. It controls involuntary actions, such as the heartbeat, breathing, movements of the alimentary canal and secretion by glands.

The spinal cord

This is a bundle of nerves arranged in cylindrical fashion, with a narrow canal at the centre. Arising from the medulla oblongata, the vertebral column and is protected by the vertebrate. The canal is filled with cerebrospinal fluid. The spinal cord relays messages from the brain to every part of the body and vice versa. It is connected to all parts of the body by nerves.

Peripheral nervous system

This consists of the nerves which connect the central nervous system with all parts of the body. Altogether, it comprises 43 pairs of nerves, 12 of which arise from the brain and 31 from the spinal cord. The former are called cranial nerves and the letter, spinal nerves. Each pair of nerves consists of a sensory nerve that carries messages to the brain or spinal cord, and a motor nerve that carries messages from the brain or spinal cord. The nerves have innumerable branches, which are included in the peripheral nervous system.

The peripheral nervous system carries impulses to and from the sensory organs, such as the skin, and conveys messages to effectors organs, like glands and muscles. It is c0ncered with the execution of both voluntary and involuntary activity. The nerve cells involved in either type of activity are of different kinds. Let us study the basic structure of a nerve cell.

Nerve cell

A nerve cell is called a neuron. The cell body, which has the nucleus, is called the cyton. From the cyton arises one or many fiber like projections, called dendrites or dendrons. These carry messages to the cell. A long fiber, called the axon, extends outwards from the cyton and ends in many branches. An axon carries impulses from the cyton. The dendrites of one neuron are connected to the axon of another, forming continuous pathways. Thus, an impulse can travel uninterruptedly from any part of the body to the brain and spinal cord. The junction of the dendrites of one neuron and the braches of the axon of another is called a synapse.



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