Which of the following is the correct sequence that describes the excitation and contraction of a skeletal muscle fiber?
1)Tropomyosin shifts and unblocks the cross-bridge binding sites.
2)Calcium is released and binds to the troponin complex.
3)Transverse tubules depolarize the sarcoplasmic reticulum.
4)The thin filaments are ratcheted across the thick filaments by the heads of the myosin molecules using energy from ATP.
5)An action potential in a motor neuron causes the axon to release acetylcholine, which depolarizes the muscle cell membrane.
A) 1 → 2 → 3 → 4 → 5
B) 2 → 1 → 3 → 5 → 4
C) 2 → 3 → 4 → 1 → 5
D) 5 → 3 → 1 → 2 → 4
E) 5 → 3 → 2 → 1 → 4

Question

Quizplus · Accepted Answer

This sequence correctly describes the steps of excitation-contraction coupling in a skeletal muscle fiber. The action potential in a motor neuron leads to the release of acetylcholine, which depolarizes the muscle cell membrane. This depolarization opens voltage-gated calcium channels, leading to calcium release from the sarcoplasmic reticulum. Calcium binds to the troponin-tropomyosin complex, shifting tropomyosin and unblocking the cross-bridge binding sites on actin. Myosin heads bind to actin, and energy from ATP is used to power the movement of the thin filaments across the thick filaments, resulting in muscle contraction.

Which of the Following Is the Correct Sequence That Describes