The characteristic cells of which the nervous tissue is composed are called nerve cells or neurons which differ greatly from each other in size and outward appearance.
Neurons consist of a cell body—the perikaryon or soma and associated processes that arise from it.
1. The nerve cell body—the perikaryon or soma:
It is a irregular shaped structure in the centre of which there lies a spherical nucleus with prominent nucleolus and fine chromatin granules but there is no centriole that is why the mature nerve cells or neurons cannot divide.
Besides these other typical cell organelles are also contained in the cytoplasm of the cell body or soma.
These are Nissl bodies composed of ribonuclear proteins and are thought to be responsible for the synthesis of proteins—possibly the enzymes concerned with acetylcholine synthesis.
The electron microscopic studies reveal that the cytoplasm of the nerve cell body or soma contains parallel arrays of the endoplasmic reticulum with cisternae and ribosome’s (Bloom and Fawcett), mitochondria and Golgi-complex, therefore the soma appears to be the side of normal cellular metabolism.
There is also present a reticular network of neurofibrils of unknown function.
The nerve cell body or soma is covered with a limiting membrane, it is a part of the bioelectrical potential generating mechanism in some neurons.
This membrane may be the site of connections with other neurons, while the cytoplasm of the soma is not involved at all directly in the bioelectrical phenomenon.
2. The nerve processes:
Since the neuron is especially differentiated to transmit impulses through the nervous system or through the organism’s body or to make connections with other neurons or with effector cells, it bears a number of processes or projections or branches, these include the dendrites (singular dendron), axon and colleterals (these are side branches of axon).