Nervous System

brain - Nervous System

The nervous system receives information about external & internal changes, communicates the information to different parts of the body & coordinates the activities of the different organs & organ systems. The nervous system includes the following parts- brain, spinal cord, nerves & the five sense organs namely eyes, ears, nose, tongue & skin.

Brain (Encephalon):

  • It is present in the head region, inside the skull bone i.e. Cranium.
  • It is about 1200-1400 gms & constitutes 98 % weight of the central nervous system.
  • The brain is divided into three parts – forebrain, midbrain & hindbrain.

The forebrain contains cerebrum which is the largest part of the brain. Cerebrum is divided into right & left cerebral hemispheres. Cerebrum controls all mental activities or Voluntary activities like memory, intelligence, reasoning, emotions & sensations.

The hindbrain contains the cerebellum (second largest part of brain) & the medulla oblongata. Medulla oblongata controls complex activities like breathing, swallowing, coughing, sneezing, blood pressure etc. 

The midbrain connects the cerebral hemispheres with the hindbrain.

Spinal cord:

  • It is a tube-like structure connected to the medulla oblongata that comes out through a hole in the skull.
  • The spinal cord is protected by the vertebral column (backbone).


  • Nerves arise both from the brain & the spinal cord.
  • They connect the brain & spinal cord to different parts of the body.
  • Nerves arising from the brain are called cranial nerves, while those arising from the spinal cord are called spinal nerves.
  • Nerves carry messages from the sense organ to the brain.
  • The brain interprets the message & decide how to react to the message received.
  • Again, it sends messages through nerves to the respective organ where the response has to be shown. 

Transmission of information:

  • The basic functional & structural unit of the nervous system is the nerve cell called the neuron.
  • The neurons are arranged end to end.
  • They transmit messages along their length from one neuron to the next.
  • This is how messages are carried from a sense organ to the spinal cord & brain & back.

The brain & spinal cord constitute the central nervous system.

The cranial nerves & spinal nerves constitute the peripheral nervous system.

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