2018 · Q23
Which one of the following statements regarding muscle contraction and relaxation is correct?
general-sciencebiology-human-body
- AIt involves movement of Zn++ ion.
- BIt involves Ca++ ion of blood.
- CIt involves release of Ca++ from sarcoplasmic reticulum (SR) and pumping Ca++ back in SR.
- DIt involves exchange of Na and K.
Explanation
Muscle contraction is triggered when an action potential releases Ca++ from the sarcoplasmic reticulum into the sarcoplasm; calcium binds troponin and exposes the myosin-binding sites on actin. Relaxation follows when Ca++ is actively pumped back into the SR. Zn++ plays no such role (A is wrong), blood calcium is not the direct trigger (B is wrong), and Na+/K+ exchange drives the action potential, not the contraction cycle (D is wrong). Hence C is correct.