Question

An increase in sodium conductance is associated with

a. The plateau phase of the ventricular muscle action potential
b. The downstroke of the skeletal muscle action potential
c. The upstroke of the smooth muscle action potential
d. The refractory period of the nerve cell action potential
e. The end-plate potential of the skeletal muscle fiber

Answer 1

The correct answer to this student's question is option (b). An increase in sodium conductance is key to the downstroke phase of the skeletal muscle action potential, where sodium rushes in and depolarizes the cell.

Step-by-step explanation:

An increase in sodium conductance is most closely associated with the downstroke of the skeletal muscle action potential. During an action potential in skeletal muscle, voltage-gated sodium channels open, allowing sodium ions to rush into the cell. This rapid influx of sodium ions causes a sharp increase in the membrane potential, resulting in the depolarization phase.

After this depolarization, potassium channels open, leading to repolarization where potassium ions leave the cell, which is visible as the downstroke in the action potential graph. Unlike cardiac muscle, which has a plateau phase primarily due to calcium ion influx, skeletal muscle lacks this prolonged depolarization phase.