- Books Name
- ACME SMART COACHING Biology Book
- Publication
- ACME SMART PUBLICATION
- Course
- CBSE Class 11
- Subject
- Biology
A neuron is a microscopic structure composed of three major parts : (i) cell body , (ii) dendrites and (iii) axon . Thell contains cytoplasm , cell organelles and certain granular bodies called Nissl's granules . Dendrites are shon branch repeatedly and project out of the cell body . They also contain Nissl's granules .
Dendrites transmit impulses towards the cell body . The axon is a long fibre , the distal end of which is bra branch terminates into a bulb - like structure called synaptic knob . Synaptic knob possess synaptic vesicle con chemicals called neurotransmitters . The axons transmit nerve impulses away from the cell body to a synapse ar neuromuscular junction.
Types of Neurons
Based on the number of axon and dendrites , the neurons are divided into three types :
Unipolar neurons have cell body with one axon only . They are found usually in the embryonic stage.
Bipolar neurons are with one axon and one dendrite . They are found in the retina of eye .
Multipolar neurons are with one axon and two or more dendrites . These are found in the cerebral cortex
On the basis of function , neurons are of two types :
Afferent neurons : These neurons carry impulses from receptors CNS . They are sensory in nature . The terminals of dendrites become modified to form receptors .
Efferent neurons : They carry impulses from CNS to effectors like muscles or glands . They are motor in nature . The axon terminals come in contact with the motor end plate to form neuromuscular junction .
Types of Axons
There are two types of axons : myelinated and non - myelinated .
The myelinated nerve fibres 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 fibres are found in spinal and cranial nerves .
Unmyelinated nerve fibre is enclosed by a Schwann cell that does form a myelin sheath around the axon . It is commonly found autonomous and the somatic neural systems .