21.3 Neuron

• Neuron is composed of three major parts, namely, cell body, dendrites and axon
• The cell body contains cytoplasm with typical cell organelles and certain granular bodies called Nissl's granules
• Short fibres which branch repeatedly and project out of the cell body also contains Nissl's granules are called Dendrites
• The axon is a long fibre, the distal end of which is branched
• Each branch terminates as a bulb like structure called synaptic knob which posses synaptic vesicles containing chemicals called neurotransmitters
• The Axons transmit nerve impulses away from the cell body to a synapse or to a neuromuscular junction
• Multipolar neuron is with one axon and two or more dendrites and is found in the cerebral cortex
• Bipolar neurons are with one axon and one dendrite and are found in the retina of eye
• Unipolar neurons have only one axon and are found in embryonic stage
• Myelinated axons are enveloped with Shwann Cells, which form a myelin sheath around the axon. They are found in spinal cord and cranial nerves
• The gaps between two adjacent myelin sheaths are called nodes of ranvier
• Non myelinated axons are enveloped by Shwann Cells that do not form a myelin sheath. They are found in ANS and SNS