tbr test 3 bio q 131

[2010premed]

An action potential results from a transient membrane depolarization along the length of an axon. Action potentials are characterized by ion-specific changes in permeability associated with specific transmembrane proteins in the membrane of the axon. Which of the following graphs BEST characterizes the ionic permeabilities of Na+ and K+ through these transmembrane proteins during an action potential?

A.

Answer: A

How would you know the difference between these 2, since both are showing that as potassium challens open, sodium chanels close?

.

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[PiBond]

Na+ channels are fast channels that open an close very quickly. they don't stay open very long so we thus would expect to see a sharp peak. also, upon receiving a stimulus the axon becomes transiently very permeable to Na+ so we'd expect a huge increase in ion permeability to Na+. Potassium channels are open for a longer duration (they're slow) and we have the constant K+ leak channels as well

 

[Charles_Carmichael]

An action potential results from a transient membrane depolarization along the length of an axon. Action potentials are characterized by ion-specific changes in permeability associated with specific transmembrane proteins in the membrane of the axon. Which of the following graphs BEST characterizes the ionic permeabilities of Na+ and K+ through these transmembrane proteins during an action potential?

A.

Answer: A

How would you know the difference between these 2, since both are showing that as potassium challens open, sodium chanels close?

.

The Na+ permeability increases faster because the Na+ channels respond quicker (ie. faster kinetics). When you look at an AP, that nearly vertical line (representing depolarization) is due to the fast kinetics of the Na+ channels. K+ permeability cannot increase that quickly (ie. you'll never see it increase as a nearly vertical line) due to the slower response of their receptors.