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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. - PowerPoint PPT Presentation
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Second lectureSecond lecture
Functions of neuroglea1-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:
I. Structural (histological) classification :
Multipolar, bipolar, unipolar and pseudonipolar neurons.
II. Functional (Physiological) classification :
1-Sensory 2-Motor or efferent neurons
Structure of neuronsStructure 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 neuronsStructure 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 neuronsStructure 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 neuronsStructure of neurons::
• B) The cell processes:
• 1- The dendrites.
• 2- The axon (axis cylinder).
Structure of neuronsStructure 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 neuronsStructure 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.