How does a neuron differ from an ordinary cell in structure? Write notes. (AS1)

A neuron is a structural and functional unit of nervous system. A neuron consists of the main cell body and cytoplasmic processes arising from it.

Cell body or cyton - It varies in size and form. It maybe irregular, spherical, oval, rounded, star-shaped or pyramidal. Like a typical cell, it consists of cytoplasm, nucleus, and cell membrane. It has abundant cytoplasm called neuroplasm and a relatively large spherical central nucleus, with a distinct nucleolus. The cytoplasm has mitochondria, Golgi apparatus, rough endoplasmic reticulum, ribosomes, lysosomes, fat globules, pigment granules, neurofibrils, neurotubules and Nissl's granules. Presence of Nissl's granules and neurofibrils is characteristics to all neurons. Neurofibrils play a role in the transmission of impulses. Neurotubulea is micro tubules which maintain the shape of the neuron. The Nissl's granules ate irregular masses of rough endoplasmic reticulum with numerous attached and free ribosomes and polysomes.

Neurites - The processes of neurons are called neurites. They are of two types :

a) Dendrites - They are usually shorter, tapering and much branched. They maybe one to several. They contain neurofibrils, neurotubules and Nissl's granules.

b) Axon - It is a single very long process of uniform thickness. It contains neurofibrils and neurotubules but not Nissl's granules, Golgi complex, ribosomes, pigment granules, fat globules etc.

A normal ordinary cell is of two types :

Procaryotic cell and eukaryotic cell.