Cerebral hemispheres, nervous-system health, Lab 6

The knee-jerk reflex is a simple example of a spinal reflex seen in healthy people. The experiment is done in pairs under adult supervision. The subject sits on a chair with one leg crossed over the other; the leg should be relaxed with muscles not tensed. The second pupil taps the tendon just below the kneecap once, gently, with the edge of the palm (or a soft rubber hammer if the teacher shows how). Receptors are excited and the impulse goes by the sensory neuron to the spinal cord and from there by a motor neuron to the thigh muscle, and the lower leg lifts a little by itself. This reflex does not depend on will. A child with pain or an injury in the knee or leg does not take part. Do not strike hard or repeat many times; do not judge the result or draw conclusions yourself: testing reflexes is a doctor’s job.