A deep tendon reflex elicited when the Achilles tendon is stretched and then struck with a tendon hammer. The normal response is reflex contraction of the calf muscles and plantar flexion of the ankle. The ankle jerk may be increased if the spinal cord is compressed above the level of the first sacral spinal nerve (which arises at the level of the second lumbar vertebra). If the nerve itself is cut or compressed the reflex is reduced or absent.
Subjects: Medicine and Health.