Q.3 (a) What do you know about human nervous system? (b) Explain neuron in detail
Answer:
(a) Human Nervous system
The nervous system in man and in other higher animals is composed of two major components.
(1) Central Nervous System (C.N.S)
A system which comprises of brain and spinal cord is called central nervous system.
(2) Peripheral Nervous System (P.N.S)
Peripheral nervous system (P.N.S) consists of nerves that arise from central nervous system and spread in different parts of body.
All these components of human nervous system are made of neurons.
(b) Neuron or Nerve cell Introduction
Nerve cell or neuron is the unit of nervous system. All the components of human nervous system are made of neurons.
Human Nervous system
The human nervous system consists of billions of neurons plus supporting (neuroglial) cells.
Function of Neurons
Neurons are specialized cells that are able to conduct nerve impulses from receptors to co-ordinators and from coordinators to effectors. In this way, they communicate with each other and with other types of body cells.
Nerve impulse
A nerve impulse is a wave of electrochemical changes that travels along the length of neuron.
Structure of neuron
Neuron consists of:
(a) Cell body
The nucleus and most of the cytoplasm of a neuron is located in its cell body :
(b) Dendrites and axon
Different processes extend out from the cell body. These are called dendrites and axon
(c) Direction of nerve impulses:
Dendrites conduct impulses towards the cell body and axons conduct impulses away from the cell body.

(d) Schwann Cells
Schwann cells are special neuroglial cells located at regular intervals along axons.
(e) Myelin Sheath
In some neurons, Schwann cells secrete a fatty layer called myelin sheath and it is located over axon. Myelin sheath is an insulator so the membrane coated with this sheath does not conduct nerve impulse. In such a neuron, impulses “jump” over the areas of myelin sheath going from node to node. Such impulses are called saltatory (jumping) impulses.
Function of Saltatory Impulses:
This increases the speed of nerve impulses.
(f) Nodes of Ranvier
Between the areas of myelin on an axon, there are non-myelinated points called the nodes of Ranvier.
Types of Neuron
On the basis of their functions, neurons are of three types:
(a) Sensory neurons conduct sensory information (nerve impulse) from receptors towards the CNS. Sensory neurons have one dendrite and one axon.
(b) Interneurons form brain and spinal cord. They receive information, interpret them and stimulate motor neurons. They have many dendrites and axons.
(c) Motor neurons carry information from interneurons to muscles or glands (effectors). They have many dendrites but only one axon.