Journeys: Skeleton. Stop 6

Knee reflex

Experiment! Sit down, cross one leg over the other and gently tap just below the knee with the edge of your hand.

Did your leg kick by itself? Tap the picture!

It kicked! And you didn't want it to, did you?

Tap again, a little below the knee, and relax your leg.

That's a reflex. The signal runs to the spinal cord in your spine and straight back to the muscle, before the brain even thinks.