Question

Which of the following must be present to allow a muscle fiber to relax?

a. High levels of ATP
b. Low levels of calcium ions
c. High levels of acetylcholine
d. Low levels of oxygen

Answer 1

To allow muscle fibre to relax, low levels of calcium ions, a) high levels of ATP, and high levels of acetylcholine must be present.

Step-by-step explanation:

For a muscle fibre to relax, several factors must be present:

1. Low levels of calcium ions: When calcium ions bind to troponin, it keeps the actin-binding sites "unshielded" and allows muscle contraction. Therefore, for relaxation to occur, calcium ions need to be removed from the sarcoplasm and the actin-binding sites must be shielded.
2. High levels of ATP: ATP is required for the process of muscle contraction. When ATP is depleted, the muscle becomes fatigued and relaxes.
3. High levels of acetylcholine: Acetylcholine is the chemical signal released by motor neurons to initiate muscle contraction. When acetylcholine levels rise, the signal to contract is reduced, leading to muscle relaxation.