Which statement best describes a reflex arc?

• A. It is a voluntary action initiated by the brain
• B. It primarily involves an effector without any sensory input
• C. It involves sensory input, CNS processing, and motor output
• D. It requires endocrine signaling

Answer: (C)

A reflex arc is a fast, automatic neural pathway that starts with a sensory receptor sensing a stimulus, carries that signal to the central nervous system for processing, and ends with a motor command to an effector (usually a muscle) to produce a quick response. This sequence—sensory input, CNS processing (often at the spinal cord with interneurons), and motor output to an effector—explains how reflexes happen without deliberate brain involvement and why they’re rapid. It’s distinct from voluntary actions, which require conscious planning by the brain, and from signaling that relies on hormones rather than neural transmission. In short, the reflex arc hinges on the ongoing chain of input → CNS integration → output to elicit a response.