November 18 Lecture - November 18, 2008 The Nervous System...

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November 18, 2008 The Nervous System Neuroglial Cells of the Central Nervous System - Astrocytes, oligodendrocytes, ependyma, and microglial cells o These cells are capable of mitosis o About half of the volume of the central nervous system are made up of these glial cells o Since these cells are used on ongoing functions, such as phagocytosis, they need to be able to replenish themselves via mitosis - Neuroglial cells Clinical Perspective o Tumours that arise from central nervous system generally arise from the various types of neuroglial cells Cancer is a non-controlled growth of cells, cells begin to replicate in rapid succession Neurons are incapable of mitotic activity, so cancer will not arise from here Two Types of Neuroglia in Peripheral Nervous System - Satellite cells and Schwann Cells o Associated with ganglion - In the peripheral nervous system, nerves run in bundles to form a ganglion o Cell bodies of neurons grouped together located in the peripheral nervous system Cell bodies that occur in the central nervous system are called a nucleus - Satellite cells o Provide structural support o Regulate chemical environment of the ganglion
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Controls the exchange of materials between the cell body and the extracellular fluid surrounding the cell body - Schwann Cells o Originators of the mylin sheath that wraps around the axon of the peripheral nerves o During neuron development, a schwann cell will wrap itself around forming axon multiple times to form a concentric series of lipid protein material wrapped around the axon which becomes the mylin sheath o Nucleus of the schwann cell lies peripheral to the mylin sheath, in an area called the neurolemma (the exterior membrane of the axon) In the central nervous system, the oligodendrocytes secrete the mylin sheath Summary - Neurons carry out communication processes, information processing, and electrical functions of the nervous system - Neuroglial are not involved in processes of the neuron, but rather preserve the physical and biochemical structure of the nerve tissue – carry out of a supportive role (for maintenance and function of the neuron) Injury to the Nervous System - Depends on location of nervous system to which the injury occurs - Neurons cannot undergo replication or repair - If nerves are part of peripheral nervous system, and axon of nerve is severed or torn, a certain amount of repair can often occur o Successful repair depends on amount of trauma, and how far any cuts are from each other o In the hours after the axon has been severed, the proximal end of the axon begins to produce sprouts which grow fairly quickly (1-1.5mm per day) and grow out in the direction of the distal (severed) portion of the axon o If mylin sheath (or if has one) is relatively intact, it acts as a tubule to direct the growth of the axonal sprouts so that they are led to the correct innervated tissue, so that it may be innervated by new axonal sprouts
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November 18 Lecture - November 18, 2008 The Nervous System...

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