Human Nervous System

All the living organisms adapt to their positions and moves as an attempt in response to the changes in the environment for their advantage or protection. Anything or any change in the environment that causes an organism to react is called stimulus, and the reaction or action of the organism in reply of the stimulus is known as a response. Some familiar stimuli are light, sound, heat, taste, smell, water, gravity and air.

The response to any stimuli is a characteristic behavior and property of the living organisms and react to stimuli with the help of Nervous system. The nervous system is an organ system which is responsible for sending messages from the brain and spinal cord to all the parts of the body and back to the brain. The basic signal in the unit of the nervous system is the Neuron.

Control and Coordination in simple multicellular organisms take place through only the Nervous system which coordinates activities of our body. It is the control system for all our actions, thinking, and behavior.

The nervous system consists of two parts namely

  1. Central Nervous System (consists of brain and spinal cord)
  2. Peripheral Nervous System ( includes all the nerves of the body)
Nervous System

Nervous System

Central Nervous System – Spinal Cord

The spinal cord is a cylindrical bundle of nerve fibers and associated tissues enclosed within the spine and link all parts of the body to the brain. It begins in continuation with medulla and extends downwards. It is enclosed in a bony cage called vertebral column and surrounded by membranes called meninges. The spinal cord is concerned with spinal reflex actions and the conduction of nerve impulses to and from the brain.

Peripheral Nervous System

Peripheral Nervous System is the lateral part of the nervous system that develops from the central nervous system which connects different parts of the body with the same. We carry out voluntary and involuntary actions with the help of peripheral nerves.


nerve 2

A Neuron is a structured and functional unit of the nervous system and unlike other cells, neurons are irregular in shape and able to conduct electrochemical signals. The different parts of a neuron are discussed below.

  • Dendrite stretches out from the cell body of a neuron, and it is the shortest fiber in the cell body.
  • Axon is the longest thread on the cell body of a neuron and has an insulating and protective sheath of myelin around it.
  • Cell body consists of cytoplasm and nucleus.
  • Synapse is the microscopic gap between a pair of adjacent neurons over which nerve impulses pass when moving from one neuron to the other.


Nerves are thread-like structures and these emerge from the brain and spinal cord responsible for carrying messages to all the parts of the body. There are three types of nerves.

  1. Sensory nerves send messages from all the senses to the brain.
  2. Motor nerves carry messages from the brain to all the muscles.
  3. Mixed nerves carry both sensory and motor nerves.

Cranial nerves begin from the brain as these nerves carry impulses to start from the central nervous system. Certain cranial nerves belong to the group of mixed nerves while certain ones fall under sensory nerves.Spinal nerves originate from the spinal cord. All the spinal nerves carry impulses to and from the central nervous system and these are part of mixed nerves.

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Practise This Question

Raj's father specifically asked him to water the plants near the ground as depicted in the image below. This is because