Audition Promenade round Cochlea autour Cochlée oreille ear organ of Corti oreille ear CRIC Montpellier Remy Pujol U254

	Innervation of the organ of Corti
	Overview / Spiral Ganglion / Neurotransmitters
	Drawings: S. Blatrix

Both types of hair cells are innervated by specific afferent and efferent systems forming a loop to and from the brainstem.

Innervation of inner (1) and outer hair cells (2)

The radial afferents (blue) and the lateral efferents (pink) innervate the inner hair cells; the spiral afferents (green) and the medial efferents (red) innervate the outer hair cells.

Inner hair cell (IHC) innervation

The IHC is synaptically connected to all type I spiral ganglion neurons (refs. a1 , c5) forming the radial afferent system (blue) going to the cochlear nuclei (CN). The lateral efferent system (pink) arising from small neurons in the ipsilateral lateral superior olivary complex (LSO) brings a feedback control to the IHC/type I afferent synapse (ref. c2, c3).

Outer hair cell (OHC) innervation

The OHC synapses with a few (at least in basal and mid-portions of the cochlea) small endings from type II spiral ganglion neurons (ref. c1), forming the spiral afferent system (green). In turn, large neurons of the medial efferent system (red), from both sides of the medial superior olivary complex (MSO), form axo-somatic synapses with the OHC (ref.a2, a3).

To better visualise the nerves within the organ of Corti, Deiters' cells have been removed.

**Schematic representation of the hair cell afferent innervation**
(from Liberman ref. a25)
	Type I spiral ganglion neurons (95% of the ganglion neurons) have a single ending radially connected to IHCs. Type II small, unmyelinated neurons spiral basally after entering the organ of Corti and branch to connect about ten OHCs, generally in the same row.