Neuron as a Structural and Functional Unit of Neural System

A neuron is a microscopic cell built of three main parts: the cell body (soma), the dendrites, and the axon. The cell body is roughly spherical and holds all the usual cell organelles (except a centriole), along with a distinctive feature — granulated rough endoplasmic reticulum known as Nissl's granules, found in both the cell body and the dendrites but absent from the axon. The plasma membrane covering the neuron's body and dendrites is called the neurilemma, while the membrane specifically around the axon is the axolemma.

Dendrites are short, repeatedly branching fibres that carry impulses toward the cell body, effectively acting as the neuron's antennae. The axon is different: it is usually a single, much longer fibre that carries impulses away from the cell body, arising from a cone-shaped region called the axon hillock — the point where, in a motor neuron, the nerve impulse is actually generated. An axon shares most organelles with the dendrites and cell body but never contains Nissl's granules or a Golgi apparatus. In peripheral nerves, the axon is wrapped by Schwann cells (a type of glial cell) which form an insulating myelin sheath; because Schwann cells don't run continuously, small unmyelinated gaps called **Nod …