Nervous system III

Nerve Tissue & the Nervous system III:
Central Nervous System:
• The principal structures of the CNS are the cerebrum, cerebellum, and spinal cord.
• It has virtually no connective tissue and is therefore a relatively soft, gel-like organ.
• When sectioned ,the cerebrum ,cerebellum, and spinal cord show regions of white (white matter) and gray (gray matter), differences caused by the differential distribution of myelin.
• Gray matter contains abundant neuronal cell bodies, dendrites, the initial unmyelinated portions of axons , astrocytes ,and microglial cells.
• Gray matter is prevalent at the cortex of the cerebrum and cerebellum, whereas white matter is present in more central regions.
Cerebral Cortex: fig.(5)
General Features:
Cerebral cortex consists of grey matter that covers the cerebral hemisphere.
The surface area of the cortex is increased due to the presence of many convolutions or gyri separated by sulci.
The cortex is made of a mixture of nerve cells, fibers, neuroglia and blood vessels.
Types of Nerve Cells
The nerve cells in cerebral cortex are of five types ,they are:
1. Pyramidal cells
• Are the most common type of neurons found in the cerebral cortex.
• Are pyramidal in shape.
• Their size ranges from 10 ?m to 120 ?m.
• Giant pyramidal cells (120 ?m) in the motor cortex are called Betz cells.
• The apices of the neurons give rise to dendritic processes which are directed towards the surface of the cortex, whereas the bases give origin to axons which forms projection fibers of the white matter.
• They are distributed in layers, 2–5, and progressively increase in size.