When a knee-jerk takes place which part is the receptor?
Answers:
When the tendon is stretched, it pulls on the muscle. In the muscle is the muscle spindle, which acts as a stretch receptor and sends action potentials to the spinal cord via neurons. These neurons synapse with alpha motor neurons (the neurons that carry instructions for movement) which will cause the muscle to contract causing a slight kick. Notice that this sensory/ motor pathway didn't involve the brain. Hence the knee-jerk reflex is a spinal cord reflex.
This may help
http://www.ifisiol.unam.mx/brain/reflex..
it's the muscles
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