Question

Please place in the correct chronological order the following events that occur during Excitation-Contraction Coupling (rest of the Lag phase events after NMJ).

Action potential propagates down the entire length of sarcolemma, including down into the transverse or T-tubule network.
Troponin undergoes a conformational (shape) change.
AP in T-tubules causes Ca^2+ to be released from the terminal cisternae of the sarcoplasmic reticulum (dihyropyridine receptors "plugged" into foot proteins or Ca^2+ release channels).
Pulling Tropomyosin off of the myosin-binding sites on individual actin proteins (shoves it deeper into the groove).
Ca^2+ diffuses out amongst the myofibrils and specifically binds to 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, 1, 5, 4, 6
c) 1, 3, 5, 2, 4, 6
d) 2, 4, 1, 3, 5, 6

Answer 1

The correct chronological order of events during excitation-contraction coupling after the NMJ (neuromuscular junction) is: action potential propagates down the sarcolemma, AP in T-tubules causes Ca2+ release from the sarcoplasmic reticulum, Ca2+ binds to Troponin-C, Troponin undergoes conformational change, Tropomyosin is pulled off the myosin-binding sites, and myosin heads bind and pull on unblocked actin molecules.

Step-by-step explanation:

The correct chronological order of events during excitation-contraction coupling after the NMJ (neuromuscular junction) is as follows:

1. Action potential propagates down the entire length of sarcolemma, including down into the T-tubule network.
2. AP in T-tubules causes Ca2+ to be released from the terminal cisternae of the sarcoplasmic reticulum (SR).
3. Ca2+ diffuses out amongst the myofibrils and specifically binds to Troponin-C subunits.
4. Troponin undergoes a conformational change.
5. Pulling Tropomyosin off of the myosin-binding sites on individual actin proteins.
6. Myosin heads can now bind and pull on unblocked actin molecules.