TBR GI and Kidney Psg I Q 2

[erythrocyte666]

Answer is C.
Anyone mind summarizing how an action potential is propagated through smooth muscle?
I initially thought enough Na ions move into a cell via a gap junction, reach threshold potential, and voltage-gated Na channels in membrane would open. TBR explanation says there is an inward Ca current that helps propagate the AP. So I’m guessing voltage-gated Ca channels open in response to depolarization?

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[bestinthewest]

You have the topics mixed up. What you just explained works for an action potential propagating via neurons but the questions specifically asks for the AP along smooth muscle fiber. Smooth muscle contractions work via the sliding filament model involving calcium, troponin, tropomyosin, the active site, and the globular myosin head. You can tell that this question doesn't expect you to know how the mechanism works at all. It was specifically tailored to see if you could relate the correct chemical to the process; in this case a muscle contraction.

 

[erythrocyte666]

I initially thought that voltage-gated Ca channels open in response to an action potential (i.e. large Na influx) and let Ca ions in to do the muscle contraction. So I guess the depolarization for the action potentials in smooth muscle fibers is caused by the Ca influx than the more commonly known Na influx?