試題詳解

4. Which of the following is a fundamental physiological difference between cardiac and skeletal muscle that prevents tetanic contractions in cardiac muscle?
(A) Cardiac muscle lacks functional T-tubules, preventing rapid excitation-contraction coupling.
(B) Cardiac muscle action potentials involve L-type Ca2+ channels, prolonging depolarization and refractory periods.
(C) The sarcoplasmic reticulum in cardiac muscle lacks ryanodine receptors, preventing sustained Ca2+ release.
(D) The pacemaker activity of cardiac muscle ensures a fixed contractile frequency, preventing summation.
(E) Cardiac muscle myosin has a significantly lower ATPase activity, preventing repeated cross-bridge cycling.