Which feature of cardiac muscle intercalated discs is directly responsible for the spread of electrical potentials between neighboring cells?

• A. Intercalated discs contain desmosomes which are directly responsible for electrochemical and metabolic coupling
• B. Intercalated discs contain gap junctions which are directly responsible for the spread of potentials between cells
• C. The arrival of an action potential allows for the sequestration of calcium in the sarcoplasmic reticulum
• D. Intercalated discs are dense regions where calcium accumulates after it is released from the sarcoplasmic reticulum

Answer: (B)

Gap junctions in intercalated discs form direct cytoplasmic connections between neighboring cardiomyocytes, allowing ions to pass and the action potential to spread rapidly from cell to cell. This electrical coupling creates a functional syncytium so the heart contracts in a coordinated way.

Desmosomes provide mechanical adhesion, not electrical communication, so they don’t mediate signal spread. The intracellular calcium handling described pertains to excitation-contraction within a single cell, not the propagation between cells. The concept that best explains the spread of electrical potentials between neighboring cardiac cells is the presence of gap junctions in the intercalated discs.