Question

Place in the correct chronological order the following events that occur during Cardiac Muscle Excitation-Contraction Coupling.

Action potential propagates down membrane and into the large T-tubule network.

Troponin undergoes a conformational (shape) change.

AP on membrane & in T-tubules open channels & causes Ca2* to enter cell from ECF and to be released from the sarcoplasmic reticulum.

Tropomyosin pulled off the myosin-binding sites on individual actin proteins (shoves it deeper into the groove).

Ca* diffuses out amongst the myofibrils and specifically binds Troponin-C subunits.

Myosin heads can now bind and pull on now "unblocked" actin molecules.

a) 1, 2, 3, 4, 5, 6
b) 3, 2, 5, 1, 4, 6
c) 6, 5, 4, 3, 2, 1
d) 2, 1, 3, 4, 5, 6

Answer 1

The correct order for Cardiac Muscle Excitation-Contraction Coupling is: action potential propagation, AP opens Ca2+ channels, Ca2+ binds to troponin, troponin changes shape, tropomyosin moves, and myosin binds actin.

Step-by-step explanation:

The correct chronological order of events during Cardiac Muscle Excitation-Contraction Coupling starts with the action potential (AP) propagating down membrane and into the T-tubule network. Following this, the AP on the membrane and in T-tubules opens channels and causes Ca2+ to enter the cell from the extracellular fluid (ECF) and to be released from the sarcoplasmic reticulum (SR). Next, Ca2+ diffuses among the myofibrils and binds specifically to Troponin-C subunits. This binding induces a conformational change in troponin. Subsequently, tropomyosin is pulled off the myosin-binding sites on actin proteins. Finally, myosin heads can now bind and pull on the now 'unblocked' actin molecules, leading to muscle contraction.