8.3—Spinal reflex arc

A reflex arc routes a stimulus from receptor through a sensory neurone and relay neurone in the CNS to a motor neurone and effector. The response is rapid and protective, reducing delay from conscious decision-making.

Synapses determine direction and integration, while antagonistic muscles can create the final movement. The brain can receive information about the stimulus even though the immediate arc is local.

Touching a hot surface activates pain receptors; flexor muscles contract and opposing extensors relax before the person consciously interprets the pain.

A reflex is not an absence of the brain and not every rapid movement is a simple spinal reflex. State receptor, CNS relay, effector and response.