What would happen if someone stabbed your leg with a syringe full of calcium and injected the calcium directly into your muscle?

a. The actin active sites would stay covered by tropomyosin.

b. Cross-bridges would form in the absence of an action potential from a motor neuron.

c. Tropomyosin would bind the calcium and change the conformation of troponin.

d. Myosin would be unable to hydrolyze ATP.

Cross-bridges would form in the absence of an action potential from a motor neuron.

Explanation:

The injected calcium ions would bind to troponin. Troponin would make tropomyosin move away from the myosin-binding sites on actin. The presence of free binding sites on the actin would be followed by the contraction cycle. This would include hydrolysis of ATP to energize myosin heads and binding of these heads to actin to form cross-bridges. Therefore, cross-bridge formation would occur without any action potential if calcium ions are injected directly into the muscle.