What is a neuron Or Nerve Cell ?

Neuron or Nerve Cell

Neuron or nerve cell is the structural and functional unit of nervous system. It can receive, conduct and transmit impulses, Neuron appears like miniature branched tree. It can reach a length of 90-100 cm. A neuron has three parts-cell body, dendrites and axon. Dendrites and axon are collectively called neurites.

  1. Cell Body (Cyton). It is the widest part of neuron which is polygonal with stellate outline. There is a prominent centrally located nucleus, various cell organelles (except centrosome) and two special structures, Nissl granules and neurofibrils. Nissl granules are ribosomes containing particles. Neurofibrils are cytoskeletal fibrils (microtubules, microfilaments and neurofilaments).
  2. Dendrites. They are short, fine, branched, protoplasmic outgrowths of the cell body. Nissl granules and neurofibrils are present. Dendrites pick up sensations and transmit the same to cell body.
  3. Axon. It is a long fibre-like process of the cell body which is specialized to carry impulses away from the cell body. It contains neurofibrils but lacks Nissl granules. Cytoplasm of axon is called axoplasm while its cell membrane is known as axolemma. Axon is branched terminally to form knobbed ends called boutons. They are meant for transmission of impulse to another neuron, cell, gland, muscle or organ.

Axon is covered by one or two sheaths. The ensheathed axon is known as nerve fibre. The single or the outer sheath is called neurilemma (= neurolemma). It is made-up of Schwann cells. When two layers are present, the inner layer is made of lipid or myelin. Such nerve fibres are called myelinated or medullated. At intervals nonmyelinated areas occur. They are called nodes of Ranvier. Myelinated or medullated nerve fibres are more efficient in transmission of impulse than non-medullated ones.