Calcium ions are released from the sarcoplasmic reticulum into the cytosol

Question

Quizplus · Accepted Answer

Calcium ions are released from the sarcoplasmic reticulum into the cytosol at the beginning of a contraction, when the muscle cell is stimulated by an action potential.

Answer: B 
 The release of calcium ions from the sarcoplasmic reticulum is triggered by the binding of acetylcholine to receptors on the muscle cell membrane. This binding causes the opening of Ca2+ release channels in the SR membrane, allowing the calcium ions to flow into the cytosol.

Answer: C 
 The sarcoplasmic reticulum actively transports calcium ions into its lumen using Ca2+ pumps, which creates a concentration gradient that drives the release of calcium ions into the cytosol.

Answer: D 
 After a contraction ends, the muscle cell actively pumps calcium ions back into the sarcoplasmic reticulum using Ca2+ pumps. This lowers the concentration of calcium ions in the cytosol and allows the muscle to relax.

Therefore, the best choice is:

Answer: A,B,C,D 
 All of these answers are correct as they describe different aspects of the release and reuptake of calcium ions during muscle contraction.

Calcium Ions Are Released from the Sarcoplasmic Reticulum into the Cytosol