Why Does Your Knee Jerk When Tapped¿ 🤔 Surgeon Reacts

Added: 2026-06-04

[00:00:00]Your knee will jerk automatically when a doctor taps it with a small hammer. This happens because the tap stimulates a tendon just below your kneecap.

[00:00:10]>> Yes, this is called a patella reflex or more generally a deep tendon reflex. We do this as a very basic part of a neurological exam. It's easy to check the integrity of the spinal cord at a specific level which sends a signal to your spinal cord. It instantly sends a signal back down to the muscles causing them to contract. And this all happens within about 30 milliseconds because it completely bypasses the brain. So this is the most important part. The kick is a pure spinal reflex. It happens without any input from your brain. This is a protective mechanism. People get confused about where you are. You feel the tap and you see your leg