Muscle stretch leads to a direct increase in firing rate of which type of nerve?
- Group Ia afferent fibers innervate intrafusal fibers of the muscle spindle. When the intrafusal fibers are stretched, the group Ia fibers fire and activate the stretch reflex, which causes the muscle to return to its resting length.
Stretch (myotatic) reflex-knee jerk
⁃ is monosynaptic.
a. Muscle is stretched, and the stretching stimulates group Ia afferent fibers.
b. Group Ia afferents synapse directly on alpha-motoneurons in the spinal cord. The pool of a-motoneurons that is activated innervates the homonymous muscle.
c. Stimulation of alpha - motoneurons causes contraction in the muscle that was stretched. As the muscle contracts, it shortens, decreasing the stretch on the muscle spindle and returning it to its original length.
d. At the same time, synergistic muscles are activated and antagonistic muscles are inhibited.