Inner ear is a complex structure of human body. It is situated in the petrous temporal bone. It contains the structures associated with hearing and balance mechanisms. The vestibule and semicircular canals are associated with balance and the cochlea is associated with hearing . I have tried my best to make it simple in my presentation.

1. Applied Anatomy of the
inner ear
Prof. (Dr) Krishna Koirala
Manipal College of Medical
Sciences
Pokhara, Nepal

2. • Innermost part of the ear
• Lies within the petrous temporal bone and houses
the vestibulocochlear organs
• Functions
− Converts mechanical signals of the middle ear
into electrical signals to transfer information to
the auditory pathway in the brain
− Maintain balance by detecting position and
motion

3. • The inner ear has two
openings into the
middle ear covered
by membranes
• The oval
window separates
the middle ear from
the vestibule
• Round window
separates the middle
ear from the scala
tympani

4.  Divisions
 Bony labyrinth : consists of a series of bony cavities within
the petrous temporal bone: cochlea, vestibule and semi-
circular canals. These structures are lined internally by
periosteum and contain perilymph
 Membranous labyrinth: lies within the bony labyrinth and
consists of the cochlear duct, utricle, saccule and semi-
circular ducts . It is filled with endolymph

5. Bony labyrinth (Vestibule, Semicircular
canals , Bony cochlea)
 Vestibule
− Central portion of bony labyrinth, ovoid in shape
− Oval window at the lateral wall, utricle and
saccule in the medial
− Openings of SCC (5) - lie on posterior, superior
and inferior walls of bony vestibule

6. Pink= Endolymph
Blue= Perilymph

7.  Semicircular canals (3)
− Lie in planes at right angles to each other
− Ampullated and non ampullated ends
− Ampullated ends contain vestibular sensory
epithelium and independently open into the
vestibule
− Non ampullated end of lateral SCC opens
separately whereas those of superior and posterior
SCCs join to form crus commune before opening in
the vestibule

8. Bony cochlea
 Coiled tube like the shell of a
snail, contains 2 ½ to 2 ¾
turns
 Height around 5mm,base
around 9 mm in diameter
 Coils turn around the modiolus
- extends along the entire
length of cochlea except for
helicotrema (small channel at
the apex)

9.  Three compartments
− Scala vestibuli
− Scala tympani
− Scala media (membranous cochlea)
 Within the modiolus lie spiral ganglion
 Cochlear nerve lies within the bony modiolus
throughout the entire length

10. Membranous labyrinth
 Membranous cochlea
− Triangular in cross section
− Bordered by Reissner's membrane, Basilar
membrane and stria vascularis
 Utricle and saccule
 Semicircular ducts
 Endolymphatic ducts and sac

12. Organ of Corti
 Sense organ of hearing
 Situated on the basilar membrane
 Components
− Tunnel of Corti
− Hair cells (outer and inner)
− Supporting cells (Deiter's, Hansen's)
− Tectorial membrane

14. Differences between inner and outer hair
cells
Inner Hair Cells Outer Hair Cells
Numbers 3500 12,000
Rows Single row Three or four rows
Shape Flask-shaped Cylindrical
Stimuli Primarily afferent Primarily efferent
Functions Transmit auditory
stimuli
Modulate inner hair
cell
Strength More Resistant to
damage
Vulnerable to
damage