BME417HW4 - BME 417 HW4 1a. In terms of figure 2, what is...

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1 BME 417 HW4 1a. In terms of figure 2, what is the absolute refractory period? From t 0 to 2ms after t 0 : it is the time during which no AP can be generated whatever the stimuli. 1b. In terms of figure 2, what is the relative refractory period? From 2ms after t 0 to 4ms after t 0 : it is the time during which the threshold for the generation of AP is higher than normal. 1c. What is the approximate maximum frequency of APs in P.P.S.? The absolute refractory period is 2ms, so the approximate maximum frequency is 1/0.002 = 500 Hz. 1d. -50mv is enough to cause a depolarization of the membrane. During the absolute refractory period no AP can be generated. But during the relative refractory period, AP will be generated once the threshold fall below -50mv, which is about 3ms after t 0 . Thus the frequency of AP generation will be 1/0.003 = 333 Hz. 1e. Compare sensory neuron to an ideal linear VCO. There are two major functional differences between the voltage sensitive K+ and Na+ ion channels. They have different gating characteristics, and they pass different ions. Na+ channels are activated at a lower potential, typically around -55mV – the threshold potential. The activation, i.e., the opening of the Na+ channels, allow the influx of Na+, causing further depolarization. The positive feedback is the basis for the rapid depolarization during the propagation of an action potential. K+ channel, on the other hand, is activated at higher potential, typically around the peak of an action
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2 potential – around +30mV. The opening of K+ channel causes the rapid repolarization of the membrane. [1] It was thought the only Na+ channels possess an inactivation gate. However, recent studies show that K+ channels, too, exhibit inactivation. The classic mechanism for the inactivation of Na+ channel is the ball and chain model. Whereby a charged peptide ‘plug’ hangs off the intracellular surface of the Na+ channel. When the membrane is depolarized, the intracellular surface of the membrane and the Na+ channel become positively charged. The negatively charged ‘plug’ is then attracted to
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This note was uploaded on 04/30/2008 for the course BIOMEDE 417 taught by Professor Cain during the Winter '07 term at University of Michigan.

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BME417HW4 - BME 417 HW4 1a. In terms of figure 2, what is...

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