Distinguish between (2) 1) Cyton and Axon 2) Receptor and Effector
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(1) Cyton : It is also called perikaryon or soma or cell body. Its granular cytoplasm is called neuroplasm which has following structures :
(i) A large, spherical, centrally placed nucleus with a single nucleolus.
(ii) Numerous fine threads called neurofibrils for the conduction of nerve impulses.
(iii) A number of small, basophilic granules called Nissl’s granules formed of rough endoplasmic reticulum with ribosomes and are sites of protein synthesis.
(iv) Neuroplasm has large number of mitochondria to provide high energy for impulse conduction.
(v) Neuroplasm may have melanophores with melanin pigment and lipochromes with orange or yellow pigment.
(vi) A mature neuron has no centriole, so it cannot divide.
(vii) A “Barr body” is often seen abutting against the inner surface of nuclear membrane of cytons in females. This has been proved to be a transformed ‘X’ chromosome.
(viii) Certain neurons having flask-shaped cytons and called purkinje cells, occur in the cerebellum of the brain.
(2) Neuron processes : The processes of neurons, called neurites, extend varying distances from the cyton and are of two types – dendrites or dendrons and an axon or axis cylinder (neuraxon).
(i) Dendron : These are several short, tapering much branched processes. The dendrites contain neurofibrils, neurotubules, Nissl’s granules and mitochondria. They conduct nerve impulse towards the cell body.
(ii) Axon : This is a single very long, cylindrical process of uniform diameter. It arises from a conical projection, the axon hillock, of the cyton. The axon contains neurofibrils and neurotubules but lacks Nissl’s granules. Axon is usually branched only terminally into slender branches called telodendria. The latter have knobbed ends called endbulbs or axon terminals or buttons or synaptic knobs or end plates. The synaptic knobs contain mitochondria and secretory vesicles.
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