Describe the structure of a neuron with a diagram.

(N/A) Neurons are the functional units of the neural system.
In the microscopic structure of a neuron,three main parts are observed:
$(1)$ Cell body,$(2)$ Dendrites,$(3)$ Axon.
$(1)$ Cell body: The body of the neuron is called the cyton or soma. The cyton may be oval,round,or stellate-shaped. The cytoplasm of the neuron is called neuroplasm. $A$ big round nucleus is present in the center of the cyton.
Neuroplasm consists of cellular organelles and small basophilic granules called Nissl's granules. Nissl's granules are mostly found near the nucleus.
$(2)$ Dendrites: These are short fibers that branch repeatedly and project out of the cyton. They also contain Nissl's granules. Dendrites transmit impulses towards the cell body.
$(3)$ Axon: It is a long fiber; the distal end of it is branched. Each branch terminates into a bulb-like structure called a synaptic knob.
Synaptic knob: It has synaptic vesicles containing chemicals called neurotransmitters.
The axon transmits nerve impulses away from the cyton to a synapse or to a neuro-muscular junction.
Types of neurons: Based on the number of axons and dendrites,neurons are divided into three types:
$(1)$ Multipolar: One axon and two or more dendrites (e.g.,cerebral cortex).
$(2)$ Bipolar: One axon and one dendrite (e.g.,retina of the eye).
$(3)$ Unipolar: Cell body with one axon only (e.g.,present in the embryonic stage).
Based on the presence or absence of a myelin sheath,neurons are classified as:
$(i)$ Myelinated neuron $(ii)$ Non-myelinated neuron.
$(i)$ Myelinated neuron: The nerve fibers are enveloped with Schwann cells,which form a myelin sheath around the axon. The gaps between two adjacent myelin sheaths are called nodes of Ranvier. Myelinated nerve fibers are found in spinal and cranial nerves.
$(ii)$ Non-myelinated neuron: They are enveloped by Schwann cells but a myelin layer is not formed around the axon. It is found in the somatic and autonomous neural systems.