The central nervous system (CNS)

 1 The Brain 

The human brain is enclosed in a bony case called the cranium . An adult human brain weighs about three pounds and consists of billions of neurons. Three layers of connective tissuses called meninges and the fluid present in these layers protect mid brain and hind brain .

A. Fore brain 

Fore brain is the largest part of the brain. It consists of three main parts,i.e .cerebrum , thalamus and hypothalamus. Cerebrum is the top most and the largest part of the brain . It is divided into right and left cerebral hemispheres. The right cerebral hemisphere control movement and activities of the left side of the body , while the left cerebral hemisphere control areas like sight , speech , smell , taste and hearing. It also control concerned with learning, thinking , intelligence, memory and voluntary 

B. Mid brain 

It is the central part of the brain. It's basic function is to transfer. Information and impulse between the fore brain and the hind brain . This part of the brain is associated with vision, hearing, sleep/wake and temperature regulation .

The mid brain also serves to control some reflexes such as changing size of the pupil to control the amount of light entering the eye.

C. Hind brain

The hind brain consists of three parts i.e Cerebellum,pons and Medulla oblongata 

Cerebellum

Is the second largest part of the brain. It is mainly concerned with posture, balance and locomotive of the body.

Pons

Is a small oval structure pressure above the medulla oblongata . It serves as a bridge for the conduction of impulse between the cerebrum , Medulla oblongata and the cerebellum.

Medulla oblongata

Connect the brain to the spinal cord . It controls heart beat, swallowing, vomiting, coughing, sneezing, digestion and breathing etc. Medulla oblongata keeps on working when the rest of the brain does not work.

2. Spinal cord

The spinal cord is extension of medulla oblongata. The spinal cord is located in the vertebral column . It is a tubular structure made up of bundle of neurons . It's length may be different according to the height of the body . The spinal cord connect that go to the body or come to the brain pass through the spinal cord . If spinal cord is damaged, message cannot move between the brain and the rest of the body . This results in paralysis.