physio1 test notes

physio1 test notes - resistance allows the forward current...

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Long-term potentiation: process in which activity at a synapse induces sustained changes in the quality of synaptic connections: important for learning Hypokalemia refers to the condition in which the concentration of potassium in the blood is low. Decreased potassium levels in the extracellular space will cause hyperpolarization of the resting membrane potential. This hyperpolarization is caused by the effect of the altered potassium gradient on resting membrane potential as defined by the Goldman equation . As a result, a greater than normal stimulus is required for depolarization of the membrane in order to initiate an action potential. Hyperkalemia: increase in K+ levels in the blood. Will shift the resting membrane potential closer to threshold, therefore giving a response to a smaller graded potential. In general, action potentials will conduct faster: 1) if axons (myelinated or unmyelinated) have larger diameters, because the lower internal longitudinal
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Unformatted text preview: resistance allows the forward current to flow farther down the axon. 2) In an unmyelinated axon, if they have a higher density of Nav. 3) If they are myelinated, because the lower capacitance and higher resistance of the internodal regions forces current to flow farther down the axon and out at the nodes, which have higher C and lower R. The high density of Nav at the nodes makes this more efficient by amplifying inward current. 4) In a myelinated axon, if the myelin sheath is thicker. In any axon, the speed with which current spreads down the length is the same (and fast!), and the time delay to open Navs is the same (a comparatively slow event of about 0.5 ms). However, if more current spreads farther down the axon before it flows out to trigger opening of Nav, then the Ap will conduct down the axon faster. This is what happens in a myelinated axon....
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This note was uploaded on 05/03/2010 for the course BISC 307L taught by Professor Herrera during the Spring '08 term at USC.

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