PHYSIOLOGY
MUSCLE CONTRACTION
|
Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
|
|
|
Binding of Ca2+ to troponin C
|
|
|
Binding of actin and myosin
|
|
|
Opening of Ca2+ release channels on the sarcoplasmic reticulum (SR)
|
|
|
Depolarization of the sarcolemmal membrane
|
Detailed explanation-1: -The answer is A [VI A 3]. In the mechanism of excitation–contraction coupling, excitation always precedes contraction. Excitation refers to the electrical activation of the muscle cell, which begins with an action potential (depolarization) in the sarcolemmal membrane that spreads to the T tubules.
Detailed explanation-2: -Depolarization of the T-tubules leads to the release of Ca2+ from the nearby sarcoplasmic reticulum (SR), followed by an increase in intracellular Ca2+ concentration, binding of Ca2+ to troponin C, and then contraction.
Detailed explanation-3: -The local membrane of the fiber will depolarize as positively charged sodium ions (Na+) enter, triggering an action potential that spreads to the rest of the membrane will depolarize, including the T-tubules. This triggers the release of calcium ions (Ca++) from storage in the sarcoplasmic reticulum (SR).