Question

multiple choice question
which of the following is correct about the way muscles contract?
a. muscle contraction occurs thanks to the sodium ions.
b. muscle contraction occurs thanks to calcium ions.
c. muscle contraction occurs with or without atp.
d. muscle contraction occurs when myosin and actin separate.

Explanation:

• Option A: Sodium ions are mainly involved in action potentials for muscle activation, not the direct cause of contraction.
• Option B: Calcium ions bind to troponin, which exposes the myosin - binding sites on actin, initiating muscle contraction. This is a key step in the sliding filament theory of muscle contraction.
• Option C: Muscle contraction requires ATP. ATP is used for the myosin heads to detach from actin and re - cock for the next cycle of contraction. So it cannot occur without ATP.
• Option D: Muscle contraction occurs when myosin and actin interact (form cross - bridges) and slide past each other, not when they separate.

Answer:

B. Muscle contraction occurs thanks to calcium ions.