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.

5 → 3 → 2 → 1 → 4

An action potential in a motor neuron causes the axon to release acetylcholine, which depolarizes the muscle cell membrane. Transverse tubules depolarize the sarcoplasmic reticulum. Calcium is released and binds to the troponin complex. Tropomyosin shifts and unblocks the cross-bridge binding sites. The thin filaments are ratcheted across the thick filaments by the heads of the myosin molecules using energy from ATP.

Explanation:

Skeletal muscle tissue is made up of fibers (the skeletal muscle fibers), which are responsible for the process of muscle contraction through the excitation and contraction of each of these fibers. All skeletal muscles have these fibers, which allows us to contract and relax them all.

The process of muscle excitation and contraction can be summarized in the following order:

An action potential in a motor neuron causes the axon to release acetylcholine, which depolarizes the muscle cell membrane. Transverse tubules depolarize the sarcoplasmic reticulum. Calcium is released and binds to the troponin complex. Tropomyosin shifts and unblocks the cross-bridge binding sites. The thin filaments are ratcheted across the thick filaments by the heads of the myosin molecules using energy from ATP.