The inner ear consists of osseous and membranous portions. The osseous portion contains the cochlea, semicircular canals, and vestibule within perilymph fluid. The membranous portion contains the cochlear duct, saccule, and utricle within endolymph fluid. The inner ear has two functional parts - the vestibular portion for balance and cochlear portion for hearing. The cochlea is divided into three canals, with the organ of Corti located in the cochlear duct where it transduces sound into electrochemical signals. The organ of Corti contains inner and outer hair cells with stereocilia that contact the tector

1. Structures of the Inner Ear
The Labyrinth
The inner ear, often referred to as
the labyrinth, is composed of two
separate physical parts. They are:
1. The osseous (bony) portion.
2. The membranous portion.

2. Structures of the Inner Ear
 Osseous portion
Contains the:
1. Perilymph fluid
2. Cochlea
3. Three semicircular canals
4. Vestibule

3. Structures of the Inner Ear
 Membranous portion
Contains the:
1. Endolymph fluid
2. Saccule
3. Utricle
4. Cochlear duct

4. Structures of the Inner Ear
 The inner ear consists of two
major functional parts. They are:
1. The vestibular portion (balance)
2. The cochlear portion (hearing)

5. Structures of the Inner Ear
 The Cochlea
It is a fluid filled cavity which is
divided into three canals. They are:
1. The scala vestibuli
2. The scala media (cochlear duct)
3. The scala tympani

6. Structures of the Inner Ear
For now, we will focus primarily on
the scala media (cochlear duct). This
is where the organ of Corti is located.

7. Structures of the Inner Ear
 The Organ of Corti
This is where the mechanical sound
energy gets transduced into
electrochemical energy.

8. Structures of the Inner Ear
 The Organ of Corti
It is located on top of the basilar
membrane and consists of
approximately one row of 3500 inner
hair cells, and three rows of outer hair
cells (each row containing over 4500
hair cells).

9. Structures of the Inner Ear
 Inner & Outer hair cells
There are some excellent photos of
both inner and outer hair cells in
Zemlin pages #474 and #475.

10. Structures of the Inner Ear
 Stereocilia
Both inner and outer hairs cells have
stereocilia on top of each hair cell.
These stereocilia contact the tectorial
membrane.

11. Structures of the Inner Ear
 Stereocilia
There are approximately 150
stereocilia on top of each outer hair
cell and 70 stereocilia on top of each
inner hair cell.

12. Structures of the Inner Ear
 Inner hair cells
They contain a chemical make up
which may aid in the transduction of
mechanical energy into
electrochemical energy.

13. Structures of the Inner Ear
 Inner hair cells
Ninety percent of the afferent VIIIth
nerve fibers are innervated by the
inner hair cells.

14. Structures of the Inner Ear
 Outer hair cells
They resemble muscle fibers,
complete with contractile proteins in
cell bodies, which enables them to
actively change shape.

15. Structures of the Inner Ear
 Outer hair cells
As the basilar membrane moves, it
serves as an “amplifier” for inner hair
cell activation.

16. Structures of the Inner Ear
 The VIIIth nerve
It moves both afferent and efferent
information to the cochlear nucleus.
Afferent is neural information from the
peripheral systems to the brain.
Efferent is neural information from the
brain to the peripheral systems.

17. Structures of the Inner Ear
 Cochlear blood supply
Is very complex, but primary supplies are
around in the scala media area.
The stria vascularis maintains the
chemical composition of the endolymph.
There are a group of small blood vessels
just below the basilar membrane which
supply the organ of Corti with nutrients.

18. Structures of the Inner Ear
 Cochlear blood supply
Please note, there is no direct contact
with the vascular system and the
structures of the cochlea. There is an
“intermediate transfer system”
through the intracochlear fluids of
each site.