reflex: Quick Facts

Written and fact-checked by

The Information Architects of Encyclopaedia Britannica

Facts

Also Known As	response

Photos

reflexive action

Diagram showing the knee jerk reflex: a reflex hammer strikes the patellar tendon below the knee, activating a stretch receptor in the quadriceps muscle. This sends a signal through a sensory neuron to the spinal cord, where it connects to a motor neuron. The motor neuron then signals the muscle to contract, causing the lower leg to kick forward. The diagram also illustrates the pathway of sensory and motor neurons and their connection in the spinal cord.

See All Images →

Topics

fixation reflex pupillary light reflex recruiting reflex yawning inhibition conditioned reflex extensor reflex flexor reflex innate reflex unconditioned reflex fight-or-flight response Stereotyped response adjustment Photoperiodism

Dig Deeper: More Articles That Discuss This Topic

Key People

Marshall Hall, detail of an engraving by J. Holl, 1839, after a portrait by J.Z. Bell

Marshall Hall

British physiologist