Question

the muscle contraction cycle will continue as long as which of the following are present?

a.) calcium ions and atp
b.) calcium ions and acetylcholine (ach)
c.) water and atp
d.) atp and acetylcholine (ach)

Explanation:

Identify the requirements for cross-bridge cycling

The muscle contraction cycle (cross-bridge cycling) requires calcium ions (\(\text{Ca}^{2+}\)) to bind to troponin, which shifts tropomyosin and exposes the myosin-binding sites on actin. It also requires ATP to provide the energy for the power stroke and to allow the myosin head to detach from actin to reset the cycle.

Evaluate the role of acetylcholine (ACh)

Acetylcholine (ACh) is necessary to initiate the action potential at the neuromuscular junction, but once the sarcoplasmic reticulum releases calcium into the sarcoplasm, the contraction cycle itself continues independently of ACh as long as calcium and ATP remain available.

Select the correct option

Option (a) correctly identifies calcium ions and ATP as the two essential components required for the contraction cycle to continue.

Answer:

• a.) Calcium ions and ATP (Correct answer)
• b.) Calcium ions and Acetylcholine (ACh)
• c.) Water and ATP
• d.) ATP and Acetylcholine (ACh)