بسم الله الرحمن الرحيم

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The neuron (nerve cell) is the structural and functional unit of the nervous system.

Nerve cell size range: 4µ up to 100µ. Cell membrane very thin Nucleus vesicular, spherical and central. No centrioles. Neurofibril of cytoplasm are parallel Nissl granules are characteristic to nerve

cell Golgi complex surround nucleus and well

developed Nerve cell inclusion include glycogen, fat

droplets, Melanin pigments in addition to lipofuscin granules (yellowish lipochrome granules).

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Types of Nerve cells

Unipolar nerve cell:

Pseudo-unipolar nerve:

Bipolar nerve cell

Multipolar nerve cell

Pyramidal cell

Types of Nerves Fibers or Axons

The axons may be naked or may be covered with:

Myelin sheathNeurolemmaBoth

1. Naked nerve fiber:No myelin sheath and no Neurolemma as

fiber in gray matter2. Myelinated nerve fiber:No Neurolemma as fibers in white matter.3. Myelinated nerve fiber with

Neurolemma as the peripheral somatic nerves outside the spinal cord.

4. Nerve fiber which are covered with Neurolemma but no with myelin sheath as the post ganglionic fibers.

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Myelin sheath Cover the axon and formed by neurolemmal

cells which surround the peripheral nervs. In brain is formed by neuroglia or neuroglial

cells. Composed of choesterol, fatty acids and

phospholipid It is interrupted by: 1. Non-myelinated Nodes of Ranvir. 2. Lanterman’s clefts: Facilitated the passage of molecules from

Schwann’s cell to myelin. To maintain the myelin sheath in a good

condition.

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