Paralysis & the Knee-jerk rxn

If you are paralyzed from the neck down, you cannot move body parts below your neck.

I was wondering, and I believe I know the answer, if you are paralyzed, and a doctor tried the knee-jerk reaction on you (ya know tap with a hammer just under the knee cap and then you kick), would your knee still kick?

I would think yes because the nerve impulse does not need to travel to the brain, but to the spinal cord and back…

You’re right. If someone’s paralyzed from a spinal cord injury, their deep-tendon reflexes not only can survive but can actually become hyperactive because they’re normally inhibited to some extent by the brain.

Not only is Bob Scene correct, but the phenomenon occurs after strokes (death or injury to part of the brain itself, usually due to lack of blood) as well as after a spinal cord injury. In both cases, the brain can no longer send inhibitory impulses to the spinal cord reflexes. So, the reflexes become hyperactive (exaggerated).

In the case of a stroke, the part of the brain where the inhibitory impulse originates has been damaged/destroyed. In the case of a spinal cord problem, the impulse can’t travel down past the point of the problem.

In addition to strokes, brain damage leading to hyperactive reflexes can be due to injury, tumors, infections (abscesses), or inflammation (eg. multiple sclerosis). The spinal cord can be damaged by a similar set of causes, but strokes affecting the cord are quite rare.