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Second lecture. Functions of neuroglea 1-Support. 2-Insulator. 3-Phagocytes (in pathological state by microglea). 4-Formation of myelin sheath in CNS by oligodendroglea. 5-Regulation of ionic environment of the neurone and thought to make up blood brain barrier (BBB) by astrocyte.
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Functions of neuroglea • 1-Support. • 2-Insulator. • 3-Phagocytes (in pathological state by microglea). • 4-Formation of myelin sheath in CNS by oligodendroglea. • 5-Regulation of ionic environment of the neurone and thought to make up blood brain barrier (BBB) by astrocyte
Classification of neurons: • Structural (histological) classification : • Multipolar, bipolar, unipolar and pseudonipolar neurons. • II. Functional (Physiological) classification : • 1-Sensory • 2-Motor or efferent neurons
Structure of neurons: • They are formed of the cell body and cell processes • A) The cell body (Soma): enlarged part of the neuron, which contains the nucleus. • inside the CNS are usually collected into groups called nuclei or centers.
Structure of neurons: • The cell bodies in the PNS usually collect to form ganglia. • inside the CNS collected into groups called nuclei or centers. The cell bodies in the PNS usually collect to form ganglia.
Structure of neurons: • The cell body is surrounded by the cell membrane and contains the following: • - Nucleus • - Neurofibrils • - Microtubules and microfilaments • - Nissl bodies • - Endoplasmic reticulum • - Golgi apparatus • - Mitochondria • - Ribosomes
Structure of neurons: • B) The cell processes: • 1- The dendrites. • 2- The axon (axis cylinder).
Structure of neurons: • The axon branches freely near its termination and makes junction with one of the following: • Dendrites of cell body of another neuron forming a neuroneural junction or synapse. • Muscle fibers to form a neuro-muscular junction. • Secretory gland to form a neuro-epithelial junction. • The axons are covered by two sheaths: • 1- Myelin (medullary) sheath: • 2- Cellular sheath (sheath of Schwann or neurilemma)
Structure of neurons: • Myelin is a white, lipid rich substance (lipoprotein complex) which acts as an electric insulator. • Myelin sheath envelops the axon except at its terminal endings. It is not a contineous layer, it is interrupted at intervals of about 0.1 to 1.0 mm by nodes of Ranvier. Through these nodes ions and water can undergo exchange with the surrounding tissues. • . In the CNS, myelin sheaths are formed by oligodendrocytes • - The axons in the PNS are surrounded by Schwann cells. • - The outer layer of the Schwann cells is called the neurilemma. • -Sheath of Schwann is essential for regreneration of the damaged • nerve fibers which occurs only in the PNS. Schwann cells are absent in the CNS.