Which one of the following statements regarding muscle contraction and relaxation is correct?
It involves movement of Zn++ ion.
It involves Ca++ ion of blood.
It involves release of Ca++ from sarcoplasmic reticulum (SR) and pumping Ca++ back in SR.
It involves exchange of Na and K.
Answer is Wrong!
Answer is Right!
This question was previously asked in
UPSC CAPF – 2018
Muscle contraction is initiated by a signal (usually from a motor neuron) that leads to a sequence of events culminating in the sliding of actin and myosin filaments. A critical step in this process is the increase in the concentration of calcium ions (Ca++) in the sarcoplasm (the cytoplasm of a muscle cell). This Ca++ is primarily stored in the sarcoplasmic reticulum (SR), a specialized endoplasmic reticulum in muscle cells. Upon receiving the signal, Ca++ is released from the SR into the sarcoplasm. These released Ca++ ions bind to regulatory proteins on the actin filaments, allowing myosin heads to bind and cause contraction. Muscle relaxation occurs when the signal stops. Ca++ ions are then actively transported back into the SR by Ca++ pumps (SERCA pumps) located on the SR membrane. The reduction in sarcoplasmic Ca++ concentration causes the regulatory proteins to block myosin binding sites again, leading to muscle relaxation. Therefore, the release of Ca++ from the SR and its subsequent pumping back into the SR are central events in muscle contraction and relaxation.
Muscle contraction and relaxation are directly regulated by the concentration of Ca++ ions in the sarcoplasm, which is controlled by the release and re-uptake of Ca++ by the sarcoplasmic reticulum.