Contraction of Myofibrils Within a Muscle Fiber Begins When

Question

Contraction of myofibrils within a muscle fiber begins when
A)sodium enters the muscle fiber
B)acetylcholine binds to ligand gates
C)calcium is released from the sarcoplasmic reticulum
D)an action potential travels t-tubules
E)calcium is moved into the sarcoplasmic reticulum

Accepted Answer

Contraction of myofibrils within a muscle fiber begins when calcium is released from the sarcoplasmic reticulum. This calcium binds to troponin, which causes a conformational change in tropomyosin, exposing binding sites on actin. This allows myosin heads to bind to actin and initiate the sliding of the filaments, resulting in muscle contraction.