Page 83 - Headlines Histology2024_Neat

Cytoplasm

• The cytoplasm of the nerve cells contains large aggregations of rER that
appear as deeply basophilic masses scattered throughout the different
cytoplasmic regions.

• These basophilic masses are called Nissl bodies or chromophilic substance
and are especially prominent in large neurons.

• The great abundance of free ribosomes and polysomes that are located in
the spaces between the rER cisternae is required to synthesis cytoplasmic
protiens that continuously flow to replace proteins used up in metabolism.

• In cases of neuronal injury, the perikaryon swells, the nucleus becomes
eccentric and Nissl bodies disappear except peripherally (chromatolysis).
This response is called axon reaction.

• The Golgi is diffuse and located mainly around the nucleus. Mitochondria
are abundant, ovoid or thread like, and randomly distributed.

• Microfilaments and microtubules are numerous and arranged in parallel
bundles throughout the perikaryon.

• Melanin pigments are found in the neuron of the substantia nigra in the
midbrain. Lipofuscin are found especially in old neurons.

• The neurons are highly differentiated cells. Centrioles are absent therefore
they cannot divide. Furthermore, from shortly after birth, new ones do not
develop from precursor cells.

• The neurons synthesize neurotransmitter substances or their precursors in
the perikaryon, they transported them along the axon to the synapse to be
released when stimulated.

Cell processes

Axon

• The axon is a long, cylindrical process of nearly uniform diameter and few
branches.

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