Muscle Q

[unsung]

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EK 1001, Q813:

Which of the following ion is involved in initiating the cardiac action potential but not skeletal action potential?

A. high concentration of extracellular sodium
B. high concentration of intracellular potassium
C. high concentration of extracellular chloride
D. high concentration of extracellular calcium

The book gives the answer as D, but I thought all muscles depended on calcium to initiate the action potential?

Edit: really don't know how I typed POSSIBLES for muscles... lol

 

[engineeredout]

EK 1001, Q813:

The book gives the answer as D, but I thought all possibles depended on calcium to initiate the action potential?

You're right, however for skeletal muscle contraction, the Ca ion buildup is in the endoplasmic reticulum of the cell, so it is not "extracellular".

 

[unsung]

You're right, however for skeletal muscle contraction, the Ca ion buildup is in the endoplasmic reticulum of the cell, so it is not "extracellular".

Oh, good pt. Thanks!

 

[RySerr21]

Oh, good pt. Thanks!

you should note that cardiac muscle does get some of its calcium from its sarcoplasmic reticulum (not endoplasmic reticulum), it just gets MORE from an extracellular source b/c the amount stored in the SR isn't enough.

 

[engineeredout]

you should note that cardiac muscle does get some of its calcium from its sarcoplasmic reticulum (not endoplasmic reticulum)

Bah, same difference 😴

 

[RySerr21]

Bah, same difference 😴

haha i know. that wasnt the main point of my "you should note" comment since it is pretty insignificant. i just noticed while i was typing it so figured i'd throw it in there.