Question

part e (5 of 6) 2 tries left which of the following is most directly responsible for the coupling of excitation to contraction of skeletal muscle fibers? action potentials. calcium ions. sodium ions. acetylcholine.

Explanation:

In skeletal muscle fibers, calcium ions bind to troponin - C, causing a conformational change that exposes the myosin - binding sites on actin. This initiates the sliding - filament mechanism of muscle contraction, directly coupling excitation (action potential) to contraction. Action potentials trigger the release of calcium ions but are not the direct coupling factor. Sodium ions are involved in the generation of action potentials. Acetylcholine is a neurotransmitter that initiates the action potential at the neuromuscular junction but is not the direct coupling agent for excitation - contraction coupling.

Answer:

B. Calcium ions