21. NEURAL CONTROL AND CO-ORDINATION
Neural (Nervous) system is a system that controls and coordinates the body activities, conducts and integrates the information and responds to stimuli.It includes brain, spinal cord and nerves.It is made up of specialized cells known as neurons.
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| Neuron (nerve cell) |
Neuron is the structural and functional unit of neural system. It is composed of
- Cell body (cyton): Contains cytoplasm, cell organelles and Nissl’s granules (granular bodies).
- Dendron: Short fibres projecting from the cyton. Their sub branches (dendrites) transmit impulses towards the cyton.
- Axon: A long fibre which transmit impulses away from the cell body. The branching of axon is called axonite. Each axonite ends as a bulb-like structure called synaptic knob.
Types of Neurons
- Unipolar: One axon. No Dendron. Found in embryo.
- Bipolar: One axon and one dendron. Found in the retina.
- Multipolar: One axon and 2 or more dendrons. Most common type. Found in the CNS & PNS.
Types of axon
- Myelinated axon: It is enveloped with Schwann cells that form a myelin sheath around the axon. Found in spinal & cranial nerves. The white coloured area, formed of myelinated nerve fibres is called white matter. Gaps b/w 2 adjacent myelin sheaths are called nodes of Ranvier.
- Non-myelinated axon: Schwann cells present but no myelin sheath. The gray coloured area without myelin sheath is called gray matter. Found in autonomous & somatic neural systems.
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