The protective mechanism that involves an external stimulus leading to an immediate muscular contraction is called
a. a depolarization potential.
b. an action potential.
c. a reflex arc.
d. a stimulus threshold.

C. a reflex arc.

Explanation:

Reflex arc is the term used to describe the body's immediate and involuntary response to arousal of a sensory nerve. For this to happen, the external stimulus is applied to the body and before reaching the brain, this stimulus receives a response in the body's marrow, causing an immediate involuntary muscle contraction without the will or awareness of the body.

answer; i do believe that the correct answer is (b)