Which of the Following Ions is the Trigger for a Muscle

Question

Which of the following ions is the trigger for a muscle contraction?
A) sodium
B) chloride
C) calcium
D) potassium
E) acetylcholine

Accepted Answer

Calcium ions are the trigger for muscle contraction. When a nerve impulse reaches the muscle cell, it triggers the release of calcium ions from the sarcoplasmic reticulum. These calcium ions bind to the protein complex troponin, which causes tropomyosin to shift its position, exposing the binding sites for myosin on actin. This allows for cross-bridge formation and muscle contraction. Sodium, chloride, potassium, and acetylcholine all play important roles in muscle function, but none of these ions are the direct trigger for muscle contraction.