The Nerve Tissue & The Nervous System
The Central Nervous System
The C.N.S consists of the cerebrum, cerebellum & spinal cord. When section, the cerebrum, cerebellum & spinal cord show region of white & gray matter. The differential distribution of myelin in the C.N.S irresponsible for these differences, the main component of white matter is myelinated axon, which producing by oligodendrocytes. White matter does not contain neuronal cell bodies.
Gray matter contains neuronal cell bodies & glial cells.
· Spinal Cord
In cross section of spinal cord which is appeared oval in shape & partial divided dorsally (posteriorly) to the right & left by found dorsal or posterior median septum, in the anteriorally (ventrally) found deep fissure called anterior (ventral) fissure.
The white matter is found peripheral & grey matter in central, which appears as H letter.
In the horizontal bar of this H opened the central canal. It is lined by ependymal cells, gray matter of the leys of the forms the anterior horns & its also form posterior horn, this is longer & narrow than the anterior horns.
· Cerebellum
The cerebellum consists of an outer cortex of gray matter & an inner white matter. The white matter consists of myelinated nerve fibers or axons these fibers are myelinated efferent fibers of the cerebellar cortex. Their ramification forms the core of the numerous cerebellar folds.
The gray matter consists of three cell layers:
o An outer molecular: contains scattered outer stellate cells whose unmyelinated axons course in horizontal direction. Descending collaterals of more deeply bascket cells arborized around Purkinje cells in basket like arrangement.
o An inner granular layer: with numerous small cells with intensely stained nuclei – axons of the granule cells extend into the molecular layer & also course horizontally as unmyelinated fibers.
The types of cells that present in this layer are:
· Small granule cell (dark nuclei & little cytoplasm).
· Scattered layer stellate cells or golgi type II cells.
Throughout the granular layer are small irregularly dispersed clear spaces called the "glomeruli" in this region, the cells are absent & synaptic complex occur.
The central layer of Purkinje cells: the Purkinje cells are pyriform in shape with ramified dendrite that external into the molecular layer, Purkinje cells are arranged in a single raw at the junction of the molecular & granular cell layers.
Their large bodies give off one of more thick dendrites which extend through the molecular layer to the surface, the thin axons leave the bases of Purkinje cells, pass through the granular layer and become myelinated as it enters the white matte
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