Ex

  Biology (NTSE/Olympiad)  

2. Tissue

Nervous Tissue

Nervous Tissue :
The nervous tissue, which contains densely packed nerve cells, called neurons (Gk. neuro = nerve), is present in the brain, spinal cord and sense organs. The neurons are specialized for conduction of nerve impulses. They receive stimuli from within or outside the body and conduct impulses (signals) which travel from one neuron to another neuron. Each neuron is composed of the following three parts.
(i) Cyton or cell body. The cell body contains the major concentration of the cytoplasm and the central nucleus of the neuron. The cell body also contains Nissl's granules, which are groups of ribosomes and rough endoplasmic reticulum.
(ii) Dendrons. These are short much-branched and tapering projections arising from the cell body. The dendrons are further branched into dendrites. They provide a large surface area for synaptic connections with other neurons. They conduct nerve impulses towards the cell body.
(iii) Axon (Nerve fibre) . The axon is a long cylindrical process of uniform diameter that arises from the axon hillock of the cyton. It shows fine branching at the terminal end. Each branch ends in a swollen structure, called synaptic knob or bouton. The axons carry impulses aways from the cell body to other neurons. The synaptic knobs of terminal branches of neuron are connected with dendrite branches of an adjacent neuron. Each such junction, in fact, has minute gap called synapse. It is meant for the transmission of nerve impulse from on neuron to the other.

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