Anatomy of inner ear

anatomy of inner ear(for undergraduates)

1. Anatomy of Inner ear Anatomy of Inner ear
Dr Ramesh Parajuli,MS
Chitwan Medical College Teaching Hospital,Bharatpur-10,Chitwan,Nepal

5. 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.

6. 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

7. Bony(osseous) labyrinth
The bony labyrinth consists of 3 parts:
1.Cochlea: anteriorly
2.Vestibule: middle
3.Semicircular canals: posteriorly
Derived from Ottic capsule

9. 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.

10.  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
Vestibule has 5 openings of 3 Semicircular
canals(SCC)

12. 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

13. Cochlea
A spiral shaped fluid
filled structure
Coiled tube making
2.5 to 2.75 turns
around a central
pyramid of bone=
Modiolus

15. Thin plate of bone winding spirally around modiolus like
a thread of screw= bony spiral lamina

16. Organ of corti through which electircal impulse(sound)
are sent along the auditory(cochlear) nerve to the brain

17. Basal turn of cochleabony bulge 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

18. Scala tympani is connected to subarachnoid space
through aqueduct of cochlea

19. Scala vestibule and scala tympani connects to each other
at the apex of cochlea  Helicotrema

20. 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

22. 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.

23. 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. Cochlear Hair CellsCochlear Hair Cells
Flask-shaped
Cylindrical shaped

28. Utricle and saccule Utricle and saccule
Macula(Sensory epithelium): concerned with
balance i.e. linear acceleration and position of head
in response to gravity

29. SemicircularSemicircular 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

30. Endolymphatic duct and sacEndolymphatic 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

31. 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. Peripheral receptors of auditory and vestibular
system

33. Vestibular Hair CellsVestibular 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

34. Structure of crista

35. Structure of macula

36. Thank you