Inner Hair Cells (IHCs)
Overview / Synapses / Physiology
Drawings: S. Blatrix; Pictures: R. Pujol

Synaptic complex below an IHC

This "synaptic complex" is composed of:
- a typical afferent synapse between the IHC (i) and an afferent auditory nerve bouton (a): a presynaptic body (red arrow) is seen ;
- and an efferent synapse (orange arrow) between lateral efferent endings (green arrows) and the auditory nerve bouton (a).

scale bar: 350 nm

  IHC (i)-auditory nerve synapse (a)



Typically, the synapse between IHC and auditory nerve endings is characterised by the presynaptic body surrounded by microvesicles (red arrow).

Pre- and postsynaptic densifications of membranes are clearly visible (pink arrows), as well as an endocytotic profile (blue arrow) in the IHC.

The glutamatergic nature of this synapse is discussed elsewhere.

scale bar: 200 nm.


 Higher magnification of the same type of synapse

In the IHC (i), a presynaptic body is seen surrounded by vesicles.

Both pre- and postsynaptic membrane thickenings, as well as an endocytotic profile (red arrow) in the IHC also characterise this afferent synapse.

Note a mitochondrium in the clear cytoplasm of the afferent dendrite (a).

scale bar: 150 nm


R. Pujol
An oblique section plane makes the plasma membranes of both the inner hair cell (i) and the afferent nerve ending (a) indistinguishable, whereas it clearly demonstrates the postsynaptic density (blue arrow) facing a presynaptic body surrounded by synaptic vesicles (red arrow).

scale bar: 100 nm

R. Pujol

 The lateral efferent synapse

Vesicular endings of the lateral efferents synapse with afferent dendrites (from type I neurons connected to the IHC (see above).

Note vesicle density in presynaptic ending and some dense material in the postsynapse (asterisk).

scale bar: 100 nm

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