human phys lec 5 - Mostneuronshavethreedistinctregions...

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Most neurons have three distinct regions Cell body (soma) contains the nucleus and most organelles Dendrites collects signals (synaptic inputs) from the surrounding cells Graded signals are produced in response to triggering synaptic events Sparse Na + channels xon nducts e action potential Axon conducts the action potential away from the cell Axon Hillock is where the axon leaves the cell High concentration of Na + channels Often were action potentials are initiated Axon terminals release chemical essengers in response to AP to messengers in response to AP to influence other cells
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Action potentials move down the axon Graded potentials do not do this
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Action potentials allow signals to move for long istances without any decrement distances without any decrement Speed of conduction is directly proportional to axon diameter. Larger xons yield higher conduction velocity (up to 200 m/s) axons yield higher conduction velocity (up to 200 m/s) Myelin sheaths around axons markedly increase conduction velocity. Cell body Axon hillock { Internodal region Node of Ranvier hwann cell Axon Myelin sheath Schwann cell
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Micrographs of myelinated peripheral nerve Cell body of Schwann cell Cross section of sciatic nerve * Axon * myelin sheath
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l N Axonal Na + channels are only at nodes Internode Node
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Na + channels (stained green) clustering at nodes of Ranvier Immunofluorescence staining Peter Schrager University of Rochester The red stain is for a protein that is known to be expressed on the regions that flank nodes
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Saltatory conduction in myelinated axons The action potential literally “ jumps ” from node to node. “Saltatory” from Latin verb saltare meaning “to jump”.
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Common Demyelinating Diseases Multiple sclerosis uillain arré ndrome Guillain Barré syndrome Chronic inflammatory demyelinating polyneuropathy Charcot Marie Tooth Disease Symptoms highly variable mptoms depend on which nerve fibers are emyelinated Symptoms depend on which nerve fibers are demyelinated. If nerve fibers that carry sensory information become demyelinated, sensory symptoms occur. If nerve fibers that carry signals to muscles become demyelinated, motor symptoms occur.
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Demyelination in spinal cord of a patient who died with multiple sclerosis
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Synapses are specialized contacts etween a neuron and its target between a neuron and its target The target can be a non neuronal tissue (e.g. muscle, gland, etc.) tt b th The target can be another neuron Some neurons do not form classic synapses and instead secrete signaling olecules into blood or ECF for diffusion to quite distant targets molecules into blood or ECF for diffusion to quite distant targets.
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This note was uploaded on 01/26/2012 for the course BIOL 3324 taught by Professor Ziburkus during the Spring '07 term at University of Houston.

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human phys lec 5 - Mostneuronshavethreedistinctregions...

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