Calcium and Action Potentials

[yanks26dmb]

TPRH Workbook... passage 15, question #1....

Flow of calcium into cells is essential to which of the following processes?

a. Opening of voltage gated sodium channels
b. Propagation of action potentials in motor neuron axons
c. Cardiac muscle contraction
d. ATP hydrolysis

I narrowed it to B and C. Correct answer is C, but I thought calcium was vital for driving acetylcholine release in presynaptic motor neurons? Can anyone explain the point I'm missing here? Thanks.

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[sillyjoe]

TPRH Workbook... passage 15, question #1....

Flow of calcium into cells is essential to which of the following processes?

a. Opening of voltage gated sodium channels
b. Propagation of action potentials in motor neuron axons
c. Cardiac muscle contraction
d. ATP hydrolysis

I narrowed it to B and C. Correct answer is C, but I thought calcium was vital for driving acetylcholine release in presynaptic motor neurons? Can anyone explain the point I'm missing here? Thanks.

You are correct in that you need calcium to enter the cell via voltage-gated calcium channels at the axon terminal for the release of neurotransmitters. However, that is not what B is saying. B is saying that calcium would be necessary for the PROPAGATION of an action potential in motor neurons. Propagation refers to an action potential traveling down the axon. Calcium is only needed at the axon terminal to allow for action potentials to go from one neuron to the next. Even with the confusion caused by this, C is certainly a better answer for the reason that the heart would not beat if you had no calcium entering the myocytes.