Inner ear

1. Anatomy Of Inner Ear

2. • The labyrinth or inner ear is an important organ of hearing and
balance.
• It consists of two portion.
(1) Bony Labyrinth
(2)Membranous Labyrinth
• There are two types of fluid in the labyrinth
(1) Perilymph - found in space between the bony and membranous
labyrinth.
(2)Endolymph- situated in membranous labyrinth.

3. Bony Labyrinth
It consists of three parts.
1) Vestibule
2) Semicircular canals
3) Cochlea
(1)Vestibule
-antral chamber of labyrinth.
-Its lateral wall lies oval window.
-Its medial wall lies two recess;spherical lodge saccule and elliptical
lodge saccule .

4. -Below elliptical recess lies opening of vestibular aqueduct where
endolymphatic duct passes.
-Its posterior wall lies five openings of semicircular canals.
(2)Semicircular Canals
-Lateral,posterior and superior semicircular canals lies right angle to
each other.
-Each canal has two ends; (1) Ampulated end which open
independently into vestibule and nonambulated end.
-Nonambulated end of posterior and superior semicircular canals unite
to form common channel called crus commune.

7. (3)Cochlea
-It is important for hearing and has two parts; bony and membranous
cochlea.
-It is a coiled tube making 2.5 to 2.75 turns around central bony
pyramid called modiolus,which base directed to internal acoustic
meatus and transmit blood vessels and nerves to the cochlea.
-Around the modious and winding spirally like the thread of a screw,
is a thin plate of bone called osseous spiral lamina.
-It divides the bony cochlea incompletely and give attachment to
basilar membrane.
-Bony bulge in the medial wall of middle ear,the promontory is due to
basal coil of cochlea.

8. The bony cochlea contains three compartments;
1)Scala vestibuli
2)Scala tympani
3)Scala media or membranous cochlea
-Scala vestibuli and scala tympani are filled with perilymph and
communicate with each other at the apex of cochlea through an
opening called helicotrema.
-Scala vestibuli is closed by the footplate of stapes which separate it
from air-filled middle ear.

9. -Scala tympani is closed by secondary tympanic membrane ;it is also
connected with subarachnoid space through the aqueduct of cochlea.

11. Membraneous Labyrinth
Consists of -
- Cochlea duct
- Utricle and Saccule
- Three semicircular ducts
- Endolymphatic duct and sac

12. 1)Cochlear duct
-also called membraneous cochlea or scala media.
-is a blind coiled tube ,appear triangular on cross-section
-Its three walls are formed by
(a) Basilar membrane –supports organ of corti
(b) Reissner’s membrane-sepsrate it from scala vestibule
(c) Stria vascularis-contains vascular endothelium and is concerned with
secretion of endolymph.
-The length of basilar membrane increase as we proceed from the basal
coil to the apical coil.

13. -For this reason,higher frequencies sound are heard at the basal coil
and lower are heard at apical coil.
2)Utricle and Saccule
-lies in posterior part of bony vestibule
-Received five openings of three semicircular ducts.
-Connected to the saccule which lies in the bony vestibule ,anterior to
the utricle and opposite the stapes footplate.
-Its exact function is not known.

14. 3)Semicircular Ducts
-Three in number and correspond exactly to three bony canals.
-Opens in the utricle.
-Ampulated end of each duct contains a thickened ridge of
neuroepithelium called crista ampularis.
4)Endolymphatic duct and Sac
-Formed by union of two ducts;one from saccule and the utricle.
-Endolymphatic sac is surgically important.It is exposed for drainage and
shunt operation in Meniere’s disease.

15. Membranous labyrinth

16. Inner Ear Fluid And Their Circulation
Two main fluid in the inner ear
-Perilymph
-Endolymph
Perilymph
-Resembles ECF and rich in Na ions.
-Fills the space between bony and membranous labyrinth.
-Communicates with CSF through aqueduct of cochlea which open into
scala tympani near the round window.

17. -There are two views regarding the formation of perilymph.
1) Is a filtrate of blood serum and is formed by capillaries of spiral
ligament.
2)Is a direct continuation of CSF and reaches the labyrinth via aqueduct
of cochlea.
Endolymph
-Fills the entire membranous labyrinth and resembles ICF,rich in K ions.
-Secreted by secretory cells of the stria vascularis of cochlea and Dark
cells.(present in utricle and near ampulated end of semicircular canals)
-There are two views regarding its flow

18. 1) Longitudinal ; endolymph from cochlea reachs saccule,utricle and
endolymphatic duct and absorbed through endolymphatic sac.
2) Radial ; endolymph is secreted by stria vascularis.

20. Blood Supply Of Labyrinth
-Through labyrinthine artery ,which is a branch of anterior-inferior
cerebellar artery but sometimes from basilar.

22. Thank You