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what are reflex arcs?
A reflex arc is the nerve pathway which makes such a fast, automatic response possible. It does not matter how brainy you are - you will always pull your hand away from a flame without thinking about it. It is in-built, or innateA reflex is an automatic response to some kind of stimulus.The key difference between a reflex action and any other action is the involvement of the brain and the lack of conscious control. By following a reflex arc, nerve impulses travel along sensory neurons from the site of stimulation to the spinal cord or brain and then back to the area of the response along motor neurons. In some reflex arcs, the sensory neurons are connected to the motor neurons by connector neurons, but either way, there is no control by the brain.The nervous pathway for the knee-jerk reaction is well-known and documented. It provides a clear example of the action of following a simple reflex arc. During the knee-jerk test, one leg is crossed over the other and kept completely relaxed. Sharply tapping the tendon just below the kneecap will result in the leg swinging upward.

The pathway for this reflex arc starts at a stretch receptor within the tendon. Hitting this receptor stimulates it, which causes it to send a nerve impulse along a sensory neuron to the spinal cord. Within the spinal cord, the nerve impulse passes from the sensory neuron to a motor neuron and travels back to the thigh muscle. When the impulse arrives at the thigh muscle, it causes it to contract and jerk the lower part of the leg upward. The person is aware that this is happening, so sensory impulses do travel from the spinal cord to the brain, but there is nothing that can be done to stop it happening.


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