anatomy of inner ear(for undergraduates)

1. Anatomy of Inner earAnatomy 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 sacculeUtricle 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