Perilymph is an
extracellular fluid located within the
inner ear. It is found within the
scala tympani and
scala vestibuli of the
cochlea
The cochlea is the part of the inner ear involved in hearing. It is a spiral-shaped cavity in the bony labyrinth, in humans making 2.75 turns around its axis, the modiolus. A core component of the cochlea is the Organ of Corti, the sensory o ...
. The ionic composition of perilymph is comparable to that of
plasma and
cerebrospinal fluid
Cerebrospinal fluid (CSF) is a clear, colorless body fluid found within the tissue that surrounds the brain and spinal cord of all vertebrates.
CSF is produced by specialised ependymal cells in the choroid plexus of the ventricles of the ...
. The major
cation in perilymph is
sodium
Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable ...
, with the values of
sodium
Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable ...
and
potassium
Potassium is the chemical element with the symbol K (from Neo-Latin '' kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmos ...
concentration in the perilymph being 138
mM and 6.9
mM, respectively. It is also named Cotunnius' liquid and liquor cotunnii for
Domenico Cotugno.
Structure
The
inner ear has two major parts, the cochlea and the vestibular organ. They are connected in a series of canals in the temporal bone referred to as the
bony labyrinth. The bone canals are separated by the membranes in parallel spaces referred to as the
membranous labyrinth. The membranous labyrinth contains
endolymph, and is surrounded by perilymph. The perilymph in the bony labyrinth serves as connection to the
cerebrospinal fluid
Cerebrospinal fluid (CSF) is a clear, colorless body fluid found within the tissue that surrounds the brain and spinal cord of all vertebrates.
CSF is produced by specialised ependymal cells in the choroid plexus of the ventricles of the ...
of the
subarachnoid space via the
perilymphatic duct
In the anatomy of the human ear, the perilymphatic duct is where the perilymphatic space (vestibule of the ear) is connected to the subarachnoid space. This works as a type of shunt to eliminate excess perilymph fluid from the perilymphatic spac ...
.
Composition
Perilymph and
endolymph have unique ionic compositions suited to their functions in regulating
electrochemical impulses of
hair cells necessary for hearing. The
electric potential
The electric potential (also called the ''electric field potential'', potential drop, the electrostatic potential) is defined as the amount of work energy needed to move a unit of electric charge from a reference point to the specific point in ...
of endolymph is ~80-90 mV more positive than perilymph due to a higher concentration of potassium cations (K
+) in endolymph and higher sodium (Na
+) in perilymph. This is referred to as the
endocochlear potential The endocochlear potential (EP; also called endolymphatic potential) is the positive voltage of 80-100mV seen in the cochlear endolymphatic spaces. Within the cochlea the EP varies in the magnitude all along its length. When a sound is presented, th ...
.
Perilymph is the fluid contained within the bony labyrinth, surrounding and protecting the membranous labyrinth; perilymph resembles extracellular fluid in composition (sodium salts are the predominant positive electrolyte) and, via the cochlear aqueduct (sometimes referred to as the "perilymphatic duct"), is in continuity with
cerebrospinal fluid
Cerebrospinal fluid (CSF) is a clear, colorless body fluid found within the tissue that surrounds the brain and spinal cord of all vertebrates.
CSF is produced by specialised ependymal cells in the choroid plexus of the ventricles of the ...
.
Endolymph is the fluid contained within the scala media of the membranous labyrinth of the inner ear and within the semicircular canals of the vestibular apparatus; endolymph resembles
intracellular fluid in composition (potassium is the main cation).
Apart from the importance in the electric cochlear potential, the perilymph also contains a large number of proteins, e.g. extracellular enzymes and immunoglobulins. These proteins are important for the immune response and metabolism among others physiological functions.
Clinical significance
It has also been suggested that perilymph and endolymph participate in a unidirectional flow that is interrupted in
Ménière's disease.
References
External links
{{Authority control
Ear
Body fluids