What does the word reflexes mean?

Reflexes are involuntary, automatic responses to stimuli. They are controlled by the spinal cord and brainstem, without the involvement of the cerebrum. Reflexes help to protect the body from harm and maintain homeostasis. For example, the knee-jerk reflex helps to protect the knee from injury by causing the leg to kick out when the knee is hit. The pupil reflex helps to maintain the proper amount of light in the eye by causing the pupils to dilate or constrict in response to changes in the light level.