MONOSYNAPTIC REFLEX:THE STRETCH REFLEX
When a muscle with an intact nerve supply is stretched, it contracts. This is the stretch reflex. The sense organ is the muscle spindle (receptors in the muscle that respond to increase in length). The action potential generated is conducted rapidly by sen-sory nerves directly to the motor nerve that supplies the same muscle. For example, if the patella tendon is tapped, a stretch reflex of the quadriceps femoris causes the leg to extend. This is known as the kneejerk (Figure 5.30). Other such reflexes can be elicitedby tapping the biceps tendon (biceps jerk), triceps tendon (triceps jerk), and Achilles tendon (anklejerk).
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