Anatomy and Physiology of the Human
J. Salvi, Ph.D., Edward Lobarinas, Ph.D.
and Wei Sun, Ph.D.
of Corti is the transducer of the cochlea.
It is the structure that translates
mechanical vibrations in the fluid of
the inner ear to equivalent electrical
impulses that can be carried up to the
brain (like an old record player that
converts the vibration of the stylus
into an electrical signal). Figure 2-2
shows each turn of the cochlea that
contains three fluid-filled compartments:
scala vestibuli (top) and scala tympani
(both filled with perilymph), and scala
media (filled with endolymph fluid).
The organ of Corti contains sensory
hair cells that lay on the basilar membrane
and convert sound into neural activity.
of Corti extends medially from the center
of the spiral toward the stria vascularis
and spiral ligament on the outside wall
(Figure 2-2). There are two types of
the aforementioned sensory hair cells.
Both contain tiny microscopic cilia
that comprise the transduction channels
that allow the outer hair cells (OHC)
and inner hair cells (IHC) to convert
mechanical energy to neural impulses.
The OHCs are located toward the “outer”
part of the organ of Corti, nearer the
stria vascularis and the IHC, as the
name suggests, are located closer to
the inner portion (center) of the organ
of Corti. There are three rows of OHC
and only one row of IHC. The base of
each OHC is supported by special (Deiter)
cells while the top surface of each
OHC is held in place by the reticular
lamina that faces the scala media. Further
from the center of the inner ear resides
the single row of IHC.
surface of the OHC sits the tectorial
membrane. This membrane is actually
in contact with the OHC, but not the
IHC. This is a cellular, gelatinous-like
structure that is connected on the inner
side of the organ of Corti only. It
is free to move on the outer side and
extends to the outermost row of OHC.
The relative movement between the sensory
cells and the tectorial membrane causes
sheering (bending or deflection) of
the hair bundles on OHC while fluid
turbulence causes movement of bundles
on the IHC. Both movements result in
hair cell action potentials that send
neurological impulses to the brain.