Cardiac muscle cells cannot fire an action potential until the muscle has relaxed from the previous...

Cardiac muscle cells cannot fire an action potential until the muscle has relaxed from the previous beat. From this you know that

Select one:

a. Ligand-gated sodium channels remain closed until calcium is pumped away from the sarcomeres

b. Voltage-gated sodium channels must be inactivated until calcium is pumped away from the sarcomeres.

c. Ligand-gated potassium channels remain open until calcium is pumped away from the sarcomeres.

d. Voltage-gated potassium channels must not open until calcium is pumped away from the sarcomeres

Expert Solution

b. Voltage-gated sodium channels must be inactivated until calcium is pumped away from the sarcomeres.

Explanation:

A soon cardiac muscle cell depolarizes and its potential shoots up to positive value, voltage gated sodium channels gets inactivated. This is followed by the opening of the voltage gated calcium channels causing the plateau phase along with opening of potassium channels . A we know that depolarization happens only when voltage gated sodium channels are activated and opened. If cardiac muscle cells are stimulated when it is depolarizing, the second action potential won't be generated as the sodium channels are still inactivated.

Sodium channels get activated only when the potential reaches the resting value by return back of calcium from sarcomere following the action potential.

This duration of action potential when another stimulus can not be able to generate new action potential is called refractory period.

Sydney Mullin answered 1 year ago

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