KEY problem set 2 - BIOLOGY 222 Winter 2012 Problem set 2...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
BIOLOGY 222 Winter 2012 Problem set 2 KEY From questions 1 to 11, information in the figures and texts are cumulative. Figure 1: Intracellular current-clamp recording of an action potential in an axon. 1. Considering the plasma membrane at rest is permeable only to Na + and K + , what is the ratio of conductances between Na + and K + (E Na = +55 mV; E K = -80 mV)? a. 1; b. 0.32; c. 0.16; d. 0.08; e. 0.0001.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
2. During the action potential, at the point of maximal depolarization, what is true? a. The conductances for Na + and K + are equal; b. Voltage-dependent Na + channels are mostly inactivated; c. The driving force for Na + is much larger than that for K + ; d. Both the Na + and K + conductances are higher than at rest; e. At this point, there is no K + current across the membrane. If conductances for Na + and K + were the same, the membrane potential would be, instead of +30 mV. At the most depolarized peak of the action potential, there is a maximum of open Na + channels and V m hyperpolarizes as more voltage-gated Na + channels inactivate; the driving force for Na + is , while for K + it is , so the driving force is actually larger for K + ; since in addition to leak channels, there are also both voltage-dependent Na + channels and K + channels open, both conductances are indeed increased when compared to rest; finally, since there is a driving force for K + and both leak and voltage-gated K + channels open, there is a K + current. 3. The fact that the action potential undershoots under the resting potential can be explained by: a. a transient decrease in the intracellular K + concentration; b. intracellular accumulation of Na + ; c. the inactivation of voltage-gated Na + channels; d. the opening of delayed rectifiers K + channels; e. both c and d. The intracellular ionic concentrations are maintained by the Na + -K + -ATPase and the ionic fluxes during the action potential are not large enough to change them; besides, reducing the K + concentration gradient would depolarize the cell, not the other way around; during the repolarization, voltage-gated Na + channels are inactivated, while delayed rectifier K + channels open with slow kinetics; since the ratio between conductance to K + and Na + is even higher than at rest, the membrane potential approaches E K even more, i.e. the membrane is hyperpolarized. 4. During the relative refractory period, a. the threshold is more depolarized than at rest; b. the population of voltage-dependent Na + channels is almost completely inactivated; c. the K + channel is below resting levels; d. there are no action potential in response to stimulatory stimuli; e. action potentials may be evoked, but with a smaller amplitude. During the relative refractory period, the threshold is more depolarized than at rest, since
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 02/02/2012 for the course BIOLOGY 222 taught by Professor Nagaya during the Winter '11 term at University of Michigan.

Page1 / 7

KEY problem set 2 - BIOLOGY 222 Winter 2012 Problem set 2...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online