What is the purpose of the knee jerk reflex?
The knee-jerk reflex — also know as the patellar reflex — is a spinal reflex, meaning that the neural circuit only goes up to the spinal cord, not all the way to the brain. The advantage of a spinal reflex is that it is fast. Nerve impulses only have to go through two neurons, so the pathway is short and there is only one spot where an impulse has to jump over to another neuron. The knee-jerk reflex is tested by tapping just below the knee on the patellar tendon. The patellar tendon runs down from the quadriceps, over the patella (kneecap), down to the lower leg. Smacking the tendon stretches it a little and sensors that detect stretching of the tendon send electrical impulses back to the spinal cord. The spinal cord automatically sends a signal back along a nerve to muscles of the quadricep. The quadricep then contracts and suddenly brings the lower leg forward. This is an involuntary contraction (i.e. it occurs without the person actually *willing* it to happen). THE PURPOSE OF THE
