Bioen305 Muscle Review

Bioen305 Muscle Review - Kortes Neural/Muscle Stuff 1....

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Korte’s Neural/Muscle Stuff 1. Membrane Biophysics a. The purpose of a cell membrane is: i. Compartmentalize ii. Cellular signaling iii. Filtering (selective permeability) iv. Capacitance v. Store potential energy (capacitor) b. Electrical stimuli trigger depolarization of cell body c. When the cell depolarizes to threshold (at the axon hillock), AP initiated d. AP travels down the axon to the axon terminal e. When myelin is present, the signal moves down the axon via saltatory conduction f. Myelin increases conduction velocity i. Decreases axon membrane leakage ii. Increases longitudinal current flow g. Capacitance = the ability of a material to hold electric charge i. Increases with surface area of plates ii. Decreases as plates become further separated iii. Specific capacitance of membrane ~ 1microFarad/cm 2 h. Ions channels ==Na/K are voltage and time dependent i. K + inside = High 4 subunits (leak Na + ) 1. Negative potential = resting position ; tilt DOWN 2. Positive potential = electrostatic respulsion = open/active; tilt out ii. Na + outside = High 3 alpha 1 Beta (blocking ball = inactive) iii. Membrane is much more permeable to K + iv. GHK Equation/Nernst Potential i. Action potential generation i. Threshold is reached (~-60--55 mV) and initiates positive feedback depolarization; opening more Na + channels at axon hillock **** ii. Propagation takes place once cell reaches threshold at axon hillock 1. Speed of propagation affected by: a. Axon diameter b. Myelination c. Membrane resistance/Internal resistance iii. Na + open until reach slightly above threshold; inactivate; turn on K + ; hyperpolarize ; Na + /K + ATPase iv. Refractory period : period during which new AP cannot be generated
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v. Relative refractory period: period when Na + channels are still open/requires higher threshold to start AP j. How do membrane channels know when to close? i.
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This note was uploaded on 04/01/2010 for the course BIOEN 305 taught by Professor Korte during the Winter '10 term at University of Washington.

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Bioen305 Muscle Review - Kortes Neural/Muscle Stuff 1....

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