The nervous tissue is specialized to receive stimuli from the environment to transform them into nerve impulses and to transmit them to the nerve centers, from where appropriate response is transmitted to another organ or part of the body which reacts to the response of the original stimulus.
Nucleus is pale staining and vesicular but the nuclear membrane stains dark with haematoxylin- chromatin is fine and dispersed. Nucleolus is single larger very prominent and may be basophilic or acidophilic. In sympathetic ganglia, the mitochondria, golgi apparatus chromophil substance or Nissl bodies and neurofibrils.
The neurofibrillae are fine cytoplasmic fibrils which form bundles are interlace in the cell body but are parallel in axon and dendrites, demonstrable by special techniques Neuroplasm is the undifferentiated part of the cytoplasm which surrounds and separates the neurofibrillae. It is also called inter fibrillar substance.
The chromophil substance also called as Nissl bodies are characteristic of nerve cell. The cell body they form irregular clumps or granules in the nueroplasm between the bundles of neurofibrils. They are basophilic. They are seen in the dendrites also but not in axons and axon hillocks and larger in motor neurons.
E.M. studies reveal that Nissl bodies are composed of dense network of rough surfaced endoplasmic retriculum with RNA granule on the outer surface of the double membranes. Their presence indicates high metabolic activity in synthesizing neuro transmitter proteins, essential for replenishment of cytoplasmic material in the axon. Following repeated stimulation during degeneration and regeneration after an injury to an axon or in other pathological conditions. Nissl material undergoes an apparent reduction or disappearance (chromatolysis).
Nerve cells may also show some inclusions or pigments under certain conditions. Two kinds of pigments are seen lipofuchsin and melanin. Lipofuchsin is yellowish or brown insoluble in usual fat solvents and appear in the form of granules dispersed throughout the cell. This pigment is not present in this newborn but appears in increasing amounts with advancing age.
Melanin appears in the form of dark brown granules in nerve cells of the factory bulb, in the floor of IV ventricle, in the substantia nigra of midbrain etc. Its significance is not known.
Dendrites appear as unmodified extensions of cell body. These branch repeatedly and terminate near the cell body to produce terminal arborization (telodentria). They contain neurofibrillae, nissl bodies and neuroplasm, like the cell body.
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