What term describes a physiological response to external stimuli?

The term that best describes a physiological response to external stimuli is "response." In the context of health science, a response encompasses the body's overall reaction to various external factors, such as environmental changes, stressors, or other stimuli. This term is broad and can include various types of reactions from the body's systems, including hormonal changes, nerve signaling, or changes in behavior.

While "reaction" and "action" are related, they are not as encompassing in the context of physiological responses. "Reaction" often implies a more immediate or instinctive response, sometimes lacking the broader physiological emphasis that "response" provides. "Action" generally refers to a behavior or physical movement rather than a physiological process.

"Reflex" specifically refers to a type of response that occurs automatically and involves a direct pathway through the nervous system, often bypassing higher brain centers. While a reflex is indeed a physiological response, it represents a narrower category within the broader concept of a response. Therefore, "response" is the most appropriate term to describe the physiological changes that occur due to external stimuli.