Simple Reflexes

How does a reflex work?

It's actually not so simple. Tapping the knee pulls on a tendon of the muscle that extends the leg. The message that the muscle is stretched goes to the spinal cord, where there is a direct connection to a motor neuron that contracts the muscle. But there are also connections to other muscles, which inhibit the contraction so that you don't react too hard. (Being able to control muscle movements without jerking is very important. A jerk, or spasm, makes movement inefficient.)