Figure 8.

Schematics of the cholinergic LL efferent synapse. LL HCs are innervated by afferent (red) and cholinergic efferent (green) fibers. Evidence for efferent cholinergic fibers contacting afferent neurons (dashed light green) is still missing. The net effect of LL efferent cholinergic activity is to hyperpolarize HCs. This is mediated by the activation of an α9* nAChR with high Ca²⁺ permeability. Subsequent activation of Ca²⁺-dependent potassium SK channels drives HC hyperpolarization. Postsynaptic cisterns (PCs) opposed to efferent terminals (Dow et al., 2018) have been proposed to participate in Ca²⁺ compartmentalization and/or Ca²⁺-induced Ca²⁺ release mechanisms.