Neurons are the longest cells in the body. Human neural systems has about 100 billion of neurons. Majority of the neurons occurs in the brain(nearly 2 billion). Fully formed neurons never divide and remain in interphase throughout the life.
Context
1. Major Parts Of Neuron
2. Types Of neuron On the basis Of Structure
3. Function Of Neural System
1. Major Parts Of Neurons
A neuron is a microscopic structure composed of the following three major parts:-
(i) Cell Body (Cyton or Soma) Like a typical cell it consists of cytoplasm, nucleus and cell membrane. The cytoplasm has typical cell organelles like mitochondria, Golgi apparatus, rough endoplasmic reticulum, ribosomes, lysosomes, certain granular bodies, and Nissl's granules.
Presence of Nissl's granules is the characteristic of all neurons.
(ii) Dendrites are usually shorter, tapering and much branched processes that project out of the cell body. They contains Nissl's granules and may be also one to several in number.
They conducts nerve impulses towards the cell of the body and are known as afferent processes (receiving processes).
(iii) Axon is a single, usually very long process of uniform thickness.
The part of cyton from which the axon arises is known as axon hillock (most sensitive part of neuron).
The axon does not have Nissl's granules, cell organelles and granular bodies. The axon ends (distal end) in a group of branches, the terminal arborisation (axon terminals).
When terminal arborization of the axon meet the dendrites of another neuron to form a synapse, each branch terminates as a bulb-like structure called synaptic knob which possesses mitochondria and secretory vesicles (containing chemicals called neurotransmitters). The axons transmits nerve impulses away from the cell of the body to a synapse or to neuromuscular junctions.
There are two types of axon
(a) Myelinated :- In myelinated nerve fibres, The Schwann cells forms myelin sheath around the axon. The gaps between two adjacent myelin sheaths are called nodes of Ranvier. Myelinated nerve fibres are found in cranial and spinal nerves and white matter of brain.
(b) Non-myelinated In non-myelinated nerve fibres, Schwann cells do not form myelin sheath around the axon and are without nodes of Ranvier. They are commonly found in autonomic and somatic neural system
2. Types Of Neurons On the Basis Of Structure
Based on the number of axons and dendrites, the neurons has been divided into three types.
(i) Multipolar neurons :- These neurons have severals dendrites as well as an axon. They are found in cerebral cortex.
(ii) Bipolar neurons :- These neurons have one dendrite as well as one axon. They are present at the retina of eye.
(iii) Unipolar neurons :- These neurons have cell body with only one axon. These are founded usually at the embryonic stage.
Main Properties of Neural Tissues, The neural tissues has two outstanding properties those were as follow :-
(a) Excitability It is the ability of nerve cells to generate an electrical impulse in response to a stimulus by altering the normal potential differences across their plasma membrane.
(b) Conductivity It is the ability of nerve cells to rapidly transmit the electrical impulses as a wave from the site of its origin along with their length in a particular direction.
3. Function Of Neural System
The nervous system serves the following important functions
(i) Control and Coordination Nervous system control as well as coordinate the working of all parts of the body. so, that it function as integrated unit. This is achieved by three overlapping processes that is :- sensory input, motor output.and integration
(ii) Memory Nervous system stores the impressions of previous stimuli and retrieves (recalls) these impressions in future. These impressions are referred to as the experiences or memory.
(iii) Homeostasis - Nervous system helps in the maintenance of the body's internal environment, i.e., homeostasis.
