Why does my doctor whack my knee with a rubber hammer?

INDIANAPOLIS (WISH) – The strike just below the kneecap is designed to test our reflexes, The tap should quickly fire your neuromuscular system triggering nerve receptors in the tendons. This kicks off nerve impulse transmission up the spinal cord. The objective is to see whether or not the lines of communication from your muscles to your brain are working properly. If the ‘knee jerk’ reaction doesn’t spontaneously occur, this could be a sign of nerve damage.

Click the video to learn more.