What causes your knee to kick when the doctor taps the top of your kneecap?

Question

Addition: I understand what reflexes are. What I want to know is if there's a specific reason that that spot triggers a subconscious response. Is it just a secret of nature? Is the nerve exposed in that spot? or what?

Answer 1

Reflex contraction of Quadriceps.

Answer 2

The tap isn't actually on the kneecap, but on the patellar tendon just below it. The sudden stretch stimulates stretch receptors (nerves), and there's a spinal reflex that causes the jerk. The impulse occurs before the signal even gets to the brain.

That, by the way, is far from the only deep tendon stretch reflex used in medicine. The Achilles, biceps, triceps, and brachioradialis are also checked pretty routinely.

Answer 3

Congratulations! you're pregnant.  That's the baby kicking back.

Answer 4

the doctor has just smacked your knee; it really just wants to kick him back

Answer 5

Nnormally when you feel something, your nerves sense it, send it to your spinal cord, to your brain, where it chooses a response and then sends it down your spinal cord and to your nerves again to elicit a response

With motions such as that, the nerve sends a message to the spinal cord and the spinal cord gives it a message to kick out, they are subconscious responses, thats why you cant stop it from happening