English: Schematics Showing the Central Origin (A) and Peripheral Projections (B) of the MOC Fibers and the Cholinergic Synapse onto OHCs in the Mature Organ of Corti (C) MOC efferent neurons are located in the superior olivary complex of the brainstem and project to the cochlea, where they make direct synaptic contacts at the base of the OHCs. At this synapse, ACh is released. It binds to α9α10 receptors present at the OHCs, leading to Ca²⁺ influx and the subsequent activation of Ca2+-dependent SK2 K+ channels and hair cell hyperpolarization. The black arrow in (A) indicates the place of electrical stimulation to activate the MOC fibers. The white arrow in (B) indicates the afferent fibers that bring the information from the IHCs to the central nervous system, and the red arrow indicates the MOC fibers. For approximately 10 d after birth (before the onset of hearing), cholinergic efferents temporarily synapse directly with IHCs (not shown in the figure) and provide a useful experimental target for the study of altered α9α10 receptors.