knee_jerk_reflex - cause the muscle to twitch. 1 2 3 S...

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1 S adav a , F ig. 46.3 Knee Jerk Reflex The neuronal circuit underlying this reflex involves sensory neurons . The neuron’s cel body (1) is located just outside the spinal cord, and its axon extends from the spinal cord to the quadriceps muscle in the front of the thigh. 1 QUADRICEPS MUSCLE SPINAL CORD When the quadriceps muscle is stretched, the stretch produces action potentials (AP’s) in the axons of the sensory neurons . These AP’s are conducted along the axon from leg to spinal cord. 1 QUADRICEPS MUSCLE SPINAL CORD S adava, Fig. 46.3 Knee Jerk Reflex In the spinal cord, the sensory axons form synapses onto the dendrites of motor neurons (2) . During the reflex these synapses produce EPSP’s, which cause the motor neurons to generate their own action potentials. 1 2 S adava, Fig. 46.3 Knee Jerk Reflex The motor neuron conducts these action potentials back through its axon to the quadriceps muscle, where it forms neuromuscular junctions (3) . At the junction, EPSP’s produce AP’s and
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Unformatted text preview: cause the muscle to twitch. 1 2 3 S adava, Fig. 46.3 Knee Jerk Reflex There is a second part to this neuronal circuit. The same sensory neuron (1) synapses with an interneuron (4) in the spinal cord. The interneuron also generates an AP. 1 4 6 5 HAMSTRING MUSCLES S adava, Fig. 46.3 Knee Jerk Reflex This interneuron has an inhibitory synapse on a different set of motor neurons (5) which innervate the hamstring muscles (6) at the back of the thigh. 1 4 6 5 HAMSTRING MUSCLES S adava, Fig. 46.3 Knee Jerk Reflex This interneuron has an inhibitory synapse on a different set of motor neurons (5) which innervate the hamstring muscles (6) at the back of the thigh. Inhibition of these motor neurons insures that the hamstring muscle is relaxed, allowing the quadriceps to move the knee. 1 4 6 5 S adava, Fig. 46.3 Knee Jerk Reflex...
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