The vestibular receptors are located in the centre of the membranous labyrinth and are bathed in 2 different types of liquid, the perilymph and the endolymph.
These liquids of the inner ear are essential for hearing and equilibration.
- The perilymph, found in the interior of the osseous labyrinth and in contact with the basal face of the hair cells, has a composition similar to that of a plasma untrafiltrate (Na+ = 140 mEq; K+ = 3 mEq) with a negligible osmotic pressure.
- The endolymph, secreted by specialised epithelial structures, the vascular striae in the cochlea and the dark cells, located on both sides of the sensory cells of the ampullary crests, is a liquid with a low protein and sodium content (15 mEq), rich in potassium (144 mEq), with a high osmotic pressure (+80 mV). It is in contact with the apical and cilia side of the hair cells.
- The endolymph plays an important role in the physiology of the vestibular hair cells.
If the concentration of calcium in the endolymph is less than 20 umol, the calcium channels of the sensory cells do not open, stopping therefore the transformation of mechanical energy in to an electrical signal.