Question

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

Explanation:

• A depolarization potential is a shift in a cell's membrane potential, not a protective muscular contraction mechanism.
• An action potential is an electrical signal in neurons, not the full protective contraction response.
• A reflex arc is the neural pathway that triggers an immediate, involuntary muscular contraction in response to an external stimulus, acting as a protective mechanism.
• A stimulus threshold is the minimum stimulus needed to trigger a response, not the mechanism itself.

Answer:

a reflex arc.