Results in flexion on the ipsilateral side and extension on the contralateral side

- Somatosensory and pain afferent fibers elicit withdrawal of the stimulated body part from the noxious stimulus.

a. Pain (e.g., touching a hot stove) stimulates the flexor reflex afferents of groups II, III, and IV.

b. The afferent fibers synapse polysynaptically (via interneurons) onto motoneurons in the spinal cord.

c. On the ipsilateral side of the pain stimulus, flexors are stimulated (they contract) and extensors are inhibited (they relax), and the arm is jerked away from the stove. On the contralateral side, flexors are inhibited and extensors are stimulated (crossed extension reflex) to maintain balance.

d. As a result of persistent neural activity in the polysynaptic circuits, an afterdischarge occurs. The afterdischarge prevents the muscle from relaxing for some time.

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Essentials of Human Physiology

Essentials of Human Physiology

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