Neuron also known as nerve cell is the structural and functional unit of nervous system. They are the longest cell of human body. It is similar to all the other cell in the body in having nucleus and all the other cell organelles in cytoplasm but it differs from the others cell by two ways:- (i) it has branches of process is called axons and dendrites. (ii) it cannot undergo division as it does not have centrosome. A single nerve cell form synapse with other neuron cell, i.e., they are not arranged in layers and they conduct impulses end to end. A neuron is composed of three major parts:- Cell body or soma, dendrites, axons.
(i) Cell Body:- The controlling part of neuron is cell body. It contains cytoplasm having a nucleus in the centre. Along with typical cell organelles it also contains certain granular bodies like Nissl's granules. Nissl's granules are small basophilic granules. They are found in the soma and dendrite but are absent in axon and axon hillock. They are membranous organelles which contains ribosomes, therefore, these bodies are concerned with the synthesis of proteins in the neurons. (ii) Dendrites:- They are short fibres which arises out from the cell. These fibres branches repeatedly to further give rise to smaller fibres. They are the one which receives the electrical impulses from the different sources and then transmits the impulse towards the cell body of the neuron. Both cell body and dendrites make up the grey matter of the brain. (iii) Axon:- They are also the nerve fibres and they are long and arises from the cell body. There may be many dendrites in each neuron but each neuron has only one long fibre-like axon. It transmits the nerve impulses away from the cell body to a synapse or neuromuscular junction.