Nervous tissues has two kinds of cells - neurons and neuroglia cells.
Neuron is the functional unit of nervous tissue. Neurons are also called nerve cells. Nervous tissues constitute the brain, spinal cord, nerves and the sensory cells and sense organs.
Like any other cell of the body, the nerve cell or neuron has the main cell body called cyton from which project out a varying number of processes, one of which is usually very long. This long fibre is called the axon.
The smaller branching processes of the cyton are called the dendrites. The cells bounded by plasma membrane, possess a nucleus and other organelles like mitochondria. The cyton also contains dark granules called Nissi bodies. These are made of RNA and Protein.
Transmission of nerve impulse - The branching dendrites receive the stimulus and transmit it through the cyton to the axon, which finally transmits it through its variously branched ends into either a muscle (to order it to contract) or to a gland (to order it to secrete). The axon constitutes the nerve fibre. The nerve fibre may or may not be covered by an extra sheath called medullary sheath secreted by sheath cells. It is made of myelin a lipid like substance. Accordingly, the nerve fibre is termed medullated and non-medullated. The medullary sheath is not continuous and is broken at nodes of Ranvier.