TPRHSW Bio Passage 76

[deleted388502]

Question on #2 on this passage:

Which of the following would most likely be abundant in active skeletal muscle cells?
A. Secretory vesicles
B. Mitochondria
C. Gap junctions with neighboring cells
D. Voltage-gated calcium channels in the plasma membrane

I put B (which is the right answer) because it seemed like the best answer in terms of the fact that "active" was in the question stem, but their answer reasoning confused me. They said that D is incorrect because "voltage-gated calcium channels are also found in cardiac but not in skeletal muscle."

I went through my physiology notes/spent some time on google, and if I'm not losing my mind, there are definitely voltage gated calcium channels in skeletal muscle.



Anyone have any insight to this?

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[DrknoSDN]

The voltage gated calcium channels of muscle are on the sarcoplasmic reticulum and not the plasma membrane. The flow of calcium is not coming from extracellular fluid, which is implied by D.

 

[Sed8&Intub8]

So it is the sarcoplasmic reticulum instead of the plasma membrane.

However, yes they both have Ca2+ channels. However, skeletal muscle uses a sodium channel to cause the action potential, which then opens up the VGCC to release Ca from the the SR. The sodium channels are more critical here. Also, what causes muscle fatigue? It's a lack of ATP, which is made by the mitochondria.

"voltage-gated calcium channels are also found in cardiac but not in skeletal muscle." That is referring to the initial action potential. Skeletal uses just sodium channels, whereas cardiac uses sodium and calcium channels in the initial action potential. It's not just about VGCC's existing, its about where and when they are existing.

 

[deleted388502]

So it is the sarcoplasmic reticulum instead of the plasma membrane.

However, yes they both have Ca2+ channels. However, skeletal muscle uses a sodium channel to cause the action potential, which then opens up the VGCC to release Ca from the the SR. The sodium channels are more critical here. Also, what causes muscle fatigue? It's a lack of ATP, which is made by the mitochondria.

"voltage-gated calcium channels are also found in cardiac but not in skeletal muscle." That is referring to the initial action potential. Skeletal uses just sodium channels, whereas cardiac uses sodium and calcium channels in the initial action potential. It's not just about VGCC's existing, its about where and when they are existing.

Ah the initial action potential part makes sense, thank you!

The voltage gated calcium channels of muscle are on the sarcoplasmic reticulum and not the plasma membrane. The flow of calcium is not coming from extracellular fluid, which is implied by D.

See, this is what my thought process was as well when I read the question, lol. When I did it I was surprised TPRH didn't have this in their answer key because I was sure it was a technicality they were trying to trip me up on.

Thanks you guys!