The internal ear, or labyrinth, contains the bony labyrinth within the petrous temporal bone and the membranous labyrinth within the bony labyrinth. The bony labyrinth contains perilymph and is made up of the cochlea, vestibule, and three semicircular canals. The membranous labyrinth contains endolymph and includes the cochlear duct, saccule, utricle, and three semicircular ducts. Disorders of the internal ear can cause issues like tinnitus, vertigo, motion sickness, and Meniere's disease.

1. LABYRINTH
INTERNAL EAR

2. Internal ear
Petrous
temporal

3. PARTS
• Outer bony labyrinth
• Inner membranous labyrinth

4. BONY LABYRINTH
• Total length – 18 mm
• Three parts from before backwards:
1. Cochlea
2. Vestibule
3. Three semicircular canals
• Contains perilymph
• It is a series of intercommunicating bony cavities
within the petrous temporal bone and contains the
membranous labyrinth.

5. MEMBRANOUS LABYRINTH
• It consist of closed system of intercommunicating
membranous sacs and ducts within the bony
labyrinth.
• It is filled with endolymph.
• It presents from before backwards three parts:
1. Cochlear duct (contains spiral organ of corti)
2. Saccule and utricle
3. Three semicircular ducts

6. BONY LABYRINTH MEMBRANOUS LABYRINTH
Endolymph
Perilymph

7. Vestibule
Cochlear canal
Posterior
Semicircular canals
Lateral
Superior/anterior
BONY LABYRINTH

8. Modiolus
Vestibule

9. VESTIBULE
VERTICAL: 5mm
A/P: 5mm
WIDTH: 3mm
FENESTRA
VESTIBULI
Semi Circular Canal
SPHERICAL RECESS
COCHLEAR RECESS

10. ELLIPTICAL
RECESS
VESTIBULAR
CREST
SPHERICAL
RECESS
COCHLEAR
RECESS

11. Semicircular canals
Superior/
anterior
Posterior
Lateral
Ampulla
Common crus
Posterior
End
Upper
End
LATERAL CANAL OF
BOTH THE SIDES
LIE IN SAME PLANE
ANTERIOR OF ONE SIDE IS
PARALLEL TO POSTERIOR
OF THE OTHER SIDE

12. Cochlear duct
Anterior
Lateral
Posterior
Vestibular nerve
Cochlear nerve
Vestibulocochlear
nerve
SEMICIRCULAR
DUCTS
MEMBRANOUS LABYRINTH

13. Round window

15. Spiral lamina
Modiolus
COCHLEAR DUCT

16. Cochlear
nerve
Spiral ganglion
Scala tympani
Scala vestibuli
Inner hair cell
outer hair cell
Reissner’s membrane / VM
Osseus cochlea
Spiral ligament
Tectorial
membrane
Cochlear duct
Cochlear modiolus
Nerve fibres
Osseus spiral lamina
Basilar
membrane
Spiral organ
of corti
ORGAN OF CORTI
SUPPORTING CELLS

17. UTRICLE
SACUULE
P
COCHLEAR DUCT
A
SEMICIRCULAR
DUCTS

18. SACCULE & UTRICLE
ENDOLYMPHATIC
SAC
DUCTUS REUNIENS

19. COCHLEA
INTERAL EAR
AQUEDUCT OF VESTIBULE
ENDOLYMPHATIC DUCT & SAC

20. VESTIBULAR NERVE
MEMBRANOUS
AMPULLA
(ANTERIOR SEMICIRCULAR CANAL)
MEMBRANOUS
AMPULLA
P
MEMBRANOUS
AMPULLA
(LATERAL
SEMICIRCULAR
CANAL)
CRUS
COMMUNE
LSCC
VESTIBULO-
COCHLEAR
NERVE
POSTERIOR
SEMICIRCULAR
CANAL
SEMICIRCULAR
CANALS VASTIBULAR
GANGLION

21. MACULA: STATIC BALANCE
VIII NERVE

22. VIII NERVE
CRISTA: KINETIC BALANCE

23. Arterial supply
Labyrithine artery
Stylomastoid artery

24. Venous drainage
Labyrithine vein – Superior petrosal
Transverse sinus
other veins drain: Into superior
petrosal
inferior
petrosal
IJV

25. Applied Anatomy
Meniere’s disease
• Due to distention of endolymph and degenerative changes
in the organ of corti.
• Patient complains of persistent attacks of nausea, vomiting, tinnitus &
progressive deafness.

26. Mechanism of Hearing

27. External
acoustic
meatus
Tympanic membrane
Ear ossicles
Cochlear canal
Cochlear
nerve

28. Rinne’s test: Patient finds vibrating tuning fork louder when placed on
mastoid process than when placed in front of affected ear
B.C > A.C

29. Weber’s test: Bone conduction is better on the side of diseased middle
ear when the vibrating tuning fork is placed on the centre
of forehead
B.C>A.C

30. APPLIED ASPECTS
• Tinnitus- peripheral cochlear disease
• Vertigo – labyrinthine dysfunction
• Motion sickness – vertigo, headache, nausea,
vomiting. Caused by excessive stimulation of
utricle and saccule.
• Meniere’s disease- paroxysmal attacks of
vertigo, tinnitus, progressive impairment of
hearing.

31. APPLIED ASPECTS
• Calorie test- it tests the pathway of internal ear
separately.