AnsWer :

Neuron is the structural and functional unit of nervous system.

It is covered by neurilemma and is made of two distinct regions as cyton and cytoplasmic extensions.

Cyton:

• Cyton or cell body is called PERIKARYON or soma. It has granular cytoplasm with large number of network of neurofibrils, various cell organelles like mitochondria, Golgi complex, RER and centrally placed nucleus. The granules present in cytoplasm are conical, rich in RNA and are involved in protein synthesis. These are called NISSL's granules.

Cytoplasmic extensions:

• Two types of cytoplasmic extensions are found arising from the cyton, namely dendrons or dendrites and axon

a. Dendrites:

• Dendrites thin, small cytoplasmic extensions seen in the periphery of the cyton or cell body of neuron.

• These are many in number and break into numerous fine branches which help to carry impulses towards the cell body and are provided with few of the neurofibrils.

b. Axon:

• Axon is the long cytoplasmic process useful in conduction of impulse away from the cell body.

• It is lined by axonal membrane and encloses cytoplasm called axoplasm.

• The axoplasm is in continuation with the cytoplasm of cyton.

• It contains large number of mitochondria, RER and neurofibrils, but lacks Nissl's granules and golgi complex.

• The axon, throughout the length is wrapped by Schwann cell which forms INSULATING myelin sheath.

• Neuron with myelin sheath are called myelinated neurons.

• In certain animals , neuron lacks the myelin sheath and thus, have non-myelinated neurons.

• The terminal end of the axon in both myelinated and non-myelinated neurons shows PRESENCE of many swollen knob like structures called telodendrons.

• They are filled with neurosecretory (acetylcholine and adrenaline) material which act as NEUROTRANSMITTER.