Structure of Neuron

---

The tissue of nervous system consist of two types of cells, those are the Nerve cells and Glial cell. The nerve cells are called Neuron and the glial cells are called neuralgia. Among these the neurons performed the function of nervous system by transmitting information from one part of the body to another and the glial cells are supporting elements.

What is Neuron?

The Neurons are the structural and functional units of nervous system.

Structure of Neuron: -

A typical structure of neuron consist of a cell body and two processes, those are Dendron and Axon.The cell body of a neuron is like other cell of the body, consisting of a nucleus and cytoplasm covered by plasma membrane. The cytoplasm contains various organelles and inclusions. In adult nerve cells, centrosome is absent or inactive so their division is not occurred. Specialised cytoplasmic organelles called Nissl granules or Nissl body made up of riboneucleoprotein are found in the cell body except in the axon hillock region from where the axon arises. These granules are also present in dendrons but absent in axon.




In our study about the structure of neuron, the Dendrons are the short and branched afferent processes which receive stimulation from other neurons and carry the information towards the cell body. In general a neuron has many dendrons. However in some neurons, the Dendron may be only single or may be absent in case. The single long efferent process of a neuron is called axon which carries impulses away from the cell body to the next neuron or the target organ , such as muscle or gland.

Axons are usually un-branched. However, they give a few small terminal branches called telodendria having swollen ends known as terminal buttons. An axon is also called nerve fibre. A neuron possesses only one axon and variable number of dendrons. If there is only one process, it is usually the axon. In such type of neurons, the cell body receives stimulation. In some specialised neurons, the axon may be absent, such as , adrenal medullary cells and amacrine cells of retina of eye.




An axon consists of the central axis cylinder containing cytoplasm i.e. axoplasm, covered by plasma membrane or axeolemma. The axoplasm and axeolemma are continuous with the cytoplasm and plasmalemma of the cell body. A nerve fiber that is axon may be myelinated or unmyelinated in the structure of neuron. In the axon which is myelinated, there is a lipid reach covering known as myelin sheathnodes of Ranvier and the portions in between adjacent nodes are called Internodes. The presence of myelin sheath increases speed of impulse conduction. Outside the myelin sheath, there is another nucleated covering called neurolemma, which is made by the Schwann shell membrane. In unmyclinated axons, the myelin sheath is absent and the axolemma is, covered by the neurolemma. In the neurons of central nervous system, neurolemma is not present. Neurolemma helps in regeneration of damaged neurons which is not possible in central nervous system.