When a doctor or nurse uses a hammer to hit a joint, like a knee, what actually causes the leg to kick? Are patients supposed to make the motion to kick when they feel the knock? Or does the hammer knock onto a nerve, that spasms the muscles into a kick?
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>Or does the hammer knock onto a nerve, that spasms the muscles into a kick?
its more like this but not exactly.
the hammer tap in the right spot triggers a signal which travels through the nerves to near the base of the spine; in the spinal cord.
then it immediately loops straight back via a different nerve and tells the relevant knee muscles to contract.
the important thing is that the signal to move your leg never reaches the brain, it short cuts the brain and goes straight back to the knee.
this is what makes it a reflex, and not a conscious decision to move your leg.
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