Quick Facts
Perilymph is the fluid contained within the space separating the membranous labyrinth from the osseous labyrinth; it is entirely separate from the endolymph (Dorland, 2011).
Structure and/or Key Feature(s)
Perilymph is an extracellular fluid that has similar consistency to cerebrospinal fluid. The perilymph of the cochlear duct is found in much smaller quantities than in the scala tympani and scala vestibuli. It is located around the spiral organ of Corti and bathes the lateral and basal aspects of the inner and outer hair cells. It fills the inner tunnel of Corti, a triangular space formed by the pillar cells and basilar membrane, and the outer tunnel (space of Nuel), the space between the outer hair cells and the outer phalangeal epithelial cells (Standring, 2016).
Perilymph of the cochlear duct is also referred to as corticolymph. It diffuses through the basilar membrane from the scala tympani and has a slightly different ionic composition to perilymph found in the scala vestibuli and tympani.
Perilymph immerses the basolateral aspects of each hair cell, while endolymph surrounds the apices of the hair cells and supporting cells. These differing ionic fluids are separated via the reticular lamina, a mosaic-like sheet that is formed at the apical regions of the hair cells and apical processes of the supporting cells. It extends from the internal supporting cells to the columnar external supporting cells but does not include either of these cell groups. The reticular lamina is strongly impermeable to the ions of the endolymph and perilymph. Given the proximity of the two fluids and their ionic differences, a resulting electrochemical gradient is generated along the reticular lamina. This forms the endocochlear potential which is necessary for the depolarization of hair cells.
Anatomical Relations
The perilymph of the cochlear duct is found in the bounded spaces of the organ of Corti. It is in direct contact with the hair cells and is confined to this region via the reticular lamina superiorly and the basilar membrane inferiorly.
Function
The perilymph of the cochlear duct plays an important role in sensory cell depolarization, as it receives the effluxing potassium from the hair cells. It also contributes to the influx of calcium through specific channels located on the lateral and basal aspects of the hair cells. Additionally, it serves as a medium between the transmission of vibration from the tympanic membrane (via the ossicles), to the disruption of endolymph to stimulate the organ of Corti.
References
Dorland, W. (2011) Dorland's Illustrated Medical Dictionary. 32nd edn. Philadelphia, USA: Elsevier Saunders.
Standring, S. (2016) Gray's Anatomy: The Anatomical Basis of Clinical Practice., 41st edition. Elsevier Limited.
