The Authors Mention That It Is Unusual for the Muscle

The authors mention that it is unusual for the muscle spindle to release glutamate (or any neurotransmitter, for that matter) because sensory nerve endings usually receive input rather than send them out. How might glutamate change the sensitivity of the stretch receptors?

A) By modulating the density of the alpha motor neurons synapsing in the neuromuscular junctions
B) By modulating the entry of calcium into the muscle during stretch
C) By modulating the sensitivity of the Golgi tendon organs
D) By changing the density of calcium-activated potassium channels
E) By modulating the density of spiral endings of Group Ia and II afferents around the nuclear chain fibers