1. Anatomy of Inner ear
Dr Meshwa Oza
Resident of otorhinolaryngology department
MK Shah medical College Ahmedabad
2.
3.
4. ● The inner(internal) ear is
called as labyrinth, from the
complexity of its shape.
● It consists of two parts:
1. The bony labyrinth: A series
of cavities within the petrous
part of the temporal bone.
2. The membranous labyrinth:
A series of communicating
membranous sacs and
ducts, contained within the
bony cavities.
5. Inner ear fluids
● Membranous labyrinth= endolymph
● Space between membranous and bony
labyrinth= perilymph
Perilymph:
Exact origin not known
Serum infiltrate, CSF
Rich in Na (similar to ECF and plasma)
Endolymph:
Origin: Stria vascularis
Rich in K ion (similar to Intracellular fluid)
Absorption: Endolymphatic sac
6. Bony(osseous) labyrinth
● The bony labyrinth consists of 3 parts:
1. Cochlea: anteriorly
2. Vestibule: middle
3. Semicircular canals: posteriorly
● Derived from Ottic capsule
7.
8. The Vestibule
● It is central part of the bony labyrinth, and is situated
medial to the tympanic cavity, behind the cochlea,
and in front of the semicircular canals.
● In its lateral or tympanic wall is the fenestra
vestibuli, closed by the base of the stapes and
annular ligament.
9. ● Two recesses:
1. Spherical recess: lodges Saccule
2. Elliptical recess: lodges Utricle
● Below elliptical recess is the opening of
aqueduct of vestibule through which passes
the endolymphatic duct
3 Semicircular
● Vestibule has 5 openings of
canals(SCC)
10.
11. Semicircular canals(SCC)
● 3 in numbers:
Lateral(horizontal)
Posterior
Superior
● Lies at right angles to each other
● Each canal has an ampullated end and non-
ampullated end
● Non-ampullated ends of PSCC and SSCC unite to
form a common channel Crus commune
● 3 SCC have 5 openings into Vestibule
12. Cochlea
● A spiral shaped fluid
filled structure
● Coiled tube making
2.5 to 2.75 turns
around a central
pyramid of bone=
Modiolus
13.
14. Thin plate of bone winding spirally around modiolus like
a thread of screw= bony spiral lamina
15. Organ of corti through which electircal impulse(sound)
are sent along the auditory(cochlear) nerve to the brain
16. ● Basal turn of cochlea bonybulge in the
medial wall of middle ear= Promontory
● Bony Cochlea contains 3 compartments:
1. Scala vestibuli: closed by stapes footplate, contains
perilymph
2. Scala tympani: closed by secondary membrane,
contains perilymph.
3. Scala media (membranous cochlea):endolymph
17. Scala tympani is connected to subarachnoid space
through aqueduct of cochlea
18. Scala vestibule and scala tympani connects to each other
at the apex of cochlea Helicotrema
19. Membranous labyrinth
● Series of communicating sacs and ducts
● Filled with endolymph
● Within walls epithelium,specialized to form sensory
receptors of cochlear and vestibular labyrinth
● It consists of
1. Cochlear duct
2. Utricle and saccule
3. Semicircular ducts
4. Endolymphatic duct and sac
20.
21. Cochlear duct(membranous cochlea)
● Blind coiled tube
● Triangular on cross section
● 3 walls:-
1. Basilar membrane: supports organ of corti
2. Reissner’s membrane(Roof of cochlear duct)
separates it from scala vestibuli
3. Stria vascularis: contains vascular epithelium.
secrets endolymph
● Cochlear duct is connected to the saccule by ductus
reuniens.
22. Organ of Corti:
contains auditory
sensory cells and
complex arrangement
of supporting cells
● Hair cells – inner and
outer
● Stereocilia or “hairs”
● electircal
impulse(sound) are
sent along the
auditory(cochlear)
nerve to the brain
27. Utricle and saccule
● Macula(Sensory epithelium): concerned with
balance i.e. linear acceleration and position of head
in response to gravity
28. Semicircular ducts
● 3 in numbers
● Ampulated and non-ampulated end
● Ampulated end of each duct contains
neuroepithelium: crista ampularis concerned with
balance i.e. Angular acceleration
29. Endolymphatic duct and sac
● Formed by the union of 2 ducts, one each from the saccule
and utricule
● Endolymphatic duct passes through the vestibular
aqueduct terminal part dilated to form endolymphatic sac
● Endolymphatic sac lies between the two layers of Dura
30. Peripheral receptors of auditory and
vestibular system
Peripheral receptors of auditory pathway:
Organ of Corti: cochlear hair cells
Peripheral receptors of vestibular pathway:
1.Cristae: located in ampullated ends of 3
Semicircular ducts
-responds to angular acceleration
2.Maculae:
Located in otolith organs(i.e. utricle and saccule)
-sense position of head in response to gravity and
linear acceleration
32. Vestibular Hair Cells
Type I vestibular cells: compare with inner cochlear hair cells (in Organ of
corti)-flask(cup)shaped
Type II vestibular cells: compare with outer cochlear hair cells-cylindrical
