Anatomy of the Sensorineural Mechanism
The Bony Labyrinth
(from Zemlin, 1998)
Three main subdivisions of the labyrinth
1. cochlea
2. semicircular canals (vestibular
system)
3. vestibule (vestibular system, mainly)
Bony labyrinth: Hard, bony
outer shell.
(from Minifie, Hixon, & Williams, 1973)
Membranous labyrinth: Fully
contained inside the bony
labyrinth; like a convolutedshaped water balloon stuff inside
the bony labyrinth.
Another view of the membranous labyrinth
(from Perkins & Kent, 1986)
Again with the membranous labyrinth, this time all by itself; i.e.,
with the entire bony labyrinth stripped away.
(from Deutsch & Richards, 1979)
Schematic and partially unrolled view of the middle ear and
labyrinth showing the scala vestibuli, the scala media (also
cochlear duct), and the scala tympani, along with the cochlear
fluids (endolymph & perilymph).
(adapted from
Zemlin, 1998)
Cuts through an unrolled and a rolled cochlea
(from Deutsch & Richards, 1979)
Cut through an unrolled cochlea
(from Deutsch & Richards, 1979)
Detail of a single cut through the cochlea showing the Organ of Corti,
8th N fibers entering through a tunnel in the spiral lamina (the
habenula perforata), the spiral ligament, and the stria vascularis.
(from Deutsch & Richards, 1979)
Notice the stria vascularis
(also area vascularis) – the
only good picture I have of
this. The s.v. secretes
endolymph.
Notice also the spiral
ligament, which
attaches the b.m. to
the bony wall of the
cochlea, and the
limbus (or limbus
spiralis), a fibrous
covering of the spiral
lamina.
(from Zemlin, Fig. 648)
modiolus
spiral ligament
Detail of the Organ of Corti
(from Stevens,1951)
Any cut through the cochlea will show 1 inner hair cell (IHC) and 3
(sometimes 4) outer hair cells (OHCs). This unit – 1 IHC and 3-4 OHCs is
referred to as a hair cell channel. There are about 3000 channels in the
human cochlea. (That number will become important later when we
discuss cochlear implants.)
Electron micrograph of a hair bundle as seen from above. Note: (1) cilia
are arranged according to height, (2) cilia are arranged in a very
distinctive pattern, variously described as a ‘W’ or sometimes a ‘V’ shape.
modiolus
spiral ligament
IHCs
modiolus
OHCs
spiral ligament
The cochlear and vestibular braches of the 8th cranial nerve
(from Deutsch & Richards, 1979)