What is initiated by a rapid influx of sodium ions into contractile cells creating a positive membrane potential inside the cell?

Answer: Action potential

Explanation:

Once stimulated, the sodium gates in the contractile cell membrane open to allow sodium ions flow inside, while potassium ions flow out leading to a depolarized membrane.

This event create a positive membrane potential inside the cell, and a net negative potential outside the membrane.

Thus, the rapid influx of sodium ions initiate action potential