LessonNo6NeurnalTissueFall10

LessonNo6NeurnalTissueFall10 - Physiology BIO 240 Lecture...

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Click to edit Master subtitle style Physiology BIO 240 Lecture No. 6 Neurons – Action Potentials, Propagation, Synapses, Neurotransmitters Fall 2010 Dr. Ana M Jimenez
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Thinking About Neurons Neurons are excitable cells because their plasma membranes are polar, Neurons receive sensory information, Neurons integrate information, and Neurons control all cells in the body (some indirectly),
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Somatic sensory information enters through dorsal root into spinal cord – synapses on, A. Motor Neuron on Ventral Horn which ends on NMJ, B. Interneuron to thalamus and cortex.
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Neuroglia Most abundant in nervous system (50-1), protect neurons and aid in their function: Oligodendrocytes (Oligo=few): Found in the CNS, form myelin in brain and spinal cord, Astrocytes (Star-like cell): Found in the CNS, Protoplasmic: Cover brain surfaces, from blood-brain-barrier, remove K+ and neurotransmitters from extracellular fluid, Fibrous: Form supportive framework in CNS, form scar tissue after injury. Ependymal cells : Found in CNS, Line cavities of brain and spinal cord, Secrete and circulate cerebrospinal fluid.
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Neuroglia Schwann cells : Found in PNS, form neurilemma around all PNS fibers, Myelin sheath around most PNS axons, Form ‘naked’ regions called ‘Nodes of Ranvier’ Aid in regeneration of damaged nerve fibers. Microglia : Found in CNS, Developmentally not related to nervous tissue, but to immune tissue, Phagocytize and destroy microorganisms, foreign matter, and dead nervous tissue.
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Schwann Cells and Oligodendrocytes Myelinate Axon Plasma membrane of these cells wraps around axon, Made of 20% protein 80% lipid, The high lipid core forms insulating, Myelination starts at 14th week of fetal development and continues after birth, Demyelinating diseases of PNS – Mystenia Gravis results in eventual paralysis and death due to asphyxation.
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Myelination of Nerve Fibers Unmyelinated Nerve Fibers : axons may not be wrapped completely by Schwann cells, One Schwann cell may partially wrap many axons. Amount of myelin and diameter of axon determines the speed at which the electrical signal travels: ( more myelin=fast , large diameter=fast ). Small Unmyelinated fibers (2-4 μm in diameter): Signals travel at 0.5-2.0 m/sec. Large Myelinated fibers (up to 20 μm in diameter): Signals travel at 120 m/sec
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Axonal Transport Proteins and other substances travel in vesicles on the cytoskeleton like ‘on a railroad’: Anterograde transport : From soma to axon, such as neurotransmitters, employs a motor protein called kinesin . Retrograde transport
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LessonNo6NeurnalTissueFall10 - Physiology BIO 240 Lecture...

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