This document provides an overview of the anatomy and embryology of the cochlea and vestibular system. It discusses the development of the membranous and bony labyrinths, as well as the basic anatomy of the cochlea including the scala vestibuli, scala tympani, and osseous spiral lamina. It also summarizes the anatomy of the bony vestibule, semicircular canals, perilymph, endolymph, sensory epithelia including hair cells and supporting cells, and the extracellular matrix components.

1. Scott
brown
learning
2020
ANATOMY OF THE COCHLEA
& VESTIBULAR SYSTEM 47
Presenter:Dr.s.vinitha

2. Membranous labyrinth
Bony labyrinth

3. EMBRYOLOGY:
OTIC CAPSULE===>Membranous Labyrinth
MESENCHYME===>Bony Labyrinth
Starts @ 3wk of IUL & Completed by 16 wk of IUL

4. Loose periotic space
Semicircular duct-------->semicircular canal
Utricle & saccule--------->Bony vestibule
Cochlear duct------------>cochlea

5. BASIC ANATOMY:

6. Bony cochlea:
2.5 to 2.75 turns of cochlea around a Bony central axis--
Modiolus
◆osseous spiral lamina winds around modiolu
s & along basilar membrane, forms partition btn s.media
&s. tympani

7. Bony cochlea parts
1.scala vestibuli
2.scala tympani
• S.vestibuli is in continuity with vestibule @ oval window, closed
by Footplate of stapes-FENESTRA VESTIBULI
• S.Tympani separated from tympanic cavity by 2° tympanic
membrane-FENESTRA COCHLEA

8. BONY VESTIBULE: Central part of Bony Labyrinth
Lateral wall:
Fenestra VESTIBULI-Oval window
Medial wall:
1.spherical recess ==>saccule It is perforated by
maculae cibrosa media( INF.VESTIBULAR NERVE)
2.Elliptical recess==>utricle. It is perforated by
macule cribrosa superior a/k/a. MIKE'S DOT
Which is a landmark in trans labyrinthine approach for nerves to
ampulla of superior & lateral semicircular canal.
3.Aqueduct of vestibule==>endolymphatic duct

10. SEMICIRCULAR CANAL:
Superior
Posterior/vertical
Lateral/horizontal
Anterolateral end of superior scc is ampulated and opens
in vestibule.
Other end joins with posterior scc to form crus commune
Ampulated end of lateral scc opens into upper parts of
vestibule

11. Membranous labyrinth
• Vestibule-saccule, utricle , endolymphatic duct & sac
• semicircular canal
• Scala media(cochlear duct) of cochlea

12. PERILYMPH:
Typical ECF ,High Na, low k+
Perilymphatic compartment(s.tympani) connects
with
arachnoid space via COCHLEAR AQUEDUCT,
Potential continuity btn CSF & perilymph
Bt the composition of two fluids differs, bcoz
perilymphatic is modified locally in inner ear

13. ENDOLYMPH
ECF, bt not a typical ECF,
high k+, low Na
Endocochlear potential +80mv
but electric potential of endolymph
in other compartment varies.

15. SENSORY EPITHELIUM:
Maculae of utricle & saccule
Cristae of Semicircular canals
Organ of corti in cochlea (Alfonso corti,anatomist)
Sensory epithelium
Sensory hair cells non sensory supporting cells

16. Each hair cell surrounded & separated by several supporting cells
Supporting cells contact with
Hair cells and other nearby
Supporting cells
There is no direct contact btn HC
Bodies of sc extend between HC
& Basement membrane

17. Reticular lamina:
The arrangement of HC & SC forms fine
network pattern ,hence known as reticular lamina.

18. Extracellular matrix:
Each sensory epithelium is covered by specific
acellular ECM
Tectorial membrane. Cupula. Otoconial memb
===>cochlea. ==>cristae. ==>macula

19. HAIR BUNDLES of HC
✓short - sterocilium
✓long -kinocilium,absent in
Mature cochlear hair cells
Sterocilium has actin filaments
Motile
Kinocilium. has microtubules
Bt non motile.

20. MET channel:
Mechanical electrical transduction channel
K+ channel
Movement of sterocilia towards kinocilia
opens MET channel& movement away from
closes met channel

21. Movement of sterocilia towards kinocilia
|
Opening of MET channel
|
K+ entry-->Depolarization
|
Opening of voltage gated ca2+ channel
|
Ca2+ binds with intracellular vesicles
|
Release of NT(Glutamate)
Action potential-->firing of neurons

22. Actin filaments in the stereocilia are closely packed.
They are cross-linked by different proteins such
epsin,
fimbrin,
fascin and plastin 1
Plastin-- second most abundant protein in stereocilia
after actin.
Loss of plastin 1 results in progressive hearing loss and
balance dysfunction and progressive thinning of stereocilia.
Composition of hair bundles:

23. Actin filaments descend from the
stereocilium into the cuticular plate as
rootlet,
The rootlet is formed of densely packed
actin filaments
TRIOBP-- actin bundling protein, helps in
formation & maintenance of Rootlet
Formation Actin
Formation & maintenance TRIOP

26. CUTICULAR PLATE:
MYOSIN types1c,6,7a,15(+) in cuticular plate and sterocilia
Immunolabelling of myosin6,7a helps to
differentiate adult HC from HC during development.
Mutation of myosin6, 7a or 15 show deafness and
balance disorders & abnormalities in their stereociliary bundles.

27. Myosin 6 mutation--sterocilias r fused & increased in l
ength. In humans causes age related hearing loss&
balance dysfn in elderly
Myosin 15 mutations--sterocilias r decreased in height
Myosin 7a mutations-->usher syndrome type1b

28. Tip link of hair bundle:
Tip link is from tip of one
sterocilia to the shaft of near
by sterocilia with increased
height
Controls opening of MET
channel
Contains 2 proteins
Cadherin(cdh 23)
Protocadherin(pcdh 15)

29. Mutations in genes encoding these proteins causing both
Hearing impairment & vestibular disturbances
Cdh 23 mutations--->usher syndrome type 1D
Pcdh 15 mutations-->usher syndrome type 1F
Tip link tension
At the point of insertion of tiplink into the shaft of the
longer stereocilium,
tip link contains proteins that regulate tip-link tension
Thereby these proteins controls opening & closing of
transduction channel

30. Tip link tension maintaining proteins
Myosin 7a
Sans
Harmonin
Mutations involving these protein encoded genes also
causes both
Hearing impairment & vestibular disturbances
Myosin 7a mutation-->usher1B
Sans mutation-->usher 1G
Harmonin mutation-->usher 1c

31. LATERAL LINKS OF Hair bundle:
It is of 3 types
• connect the shaft of one stereocilium to all its neighbours.
• Lateral links may have a role in holding the bundle together,
and stabilises it .
• Helps stereocilias in a hair bundle to move as a single unit.
• Mutations leads to splaying of sterocilia(loss of effective met) &
causes both Hearing impairment & vestibular disturbances

32. Ankle link: connect stereocilia
at their proximal ends.
Shaft connectors: present along the
mid-region of the stereociliary shaft
Top connectors: located just below
the level of tip link

33. GENERAL CHARACTERISTICS OF SUPPORTING CELLS:
 The supporting cells provide mechanical support to the
epithelium(hair cells)
 cell bodies of sc contact each other & rest on the basement membrane
that underlies the sensory epithelium
 Supporting cells are functionally coupled to each other by large gap
junctions. therefore they act as functional syncytium
 Gap jn not present in HC
 Pore forming channel proteins of one cell r in direct contact with pore
forming channel proteins of neighborhood cells

35.  The protein subunits that form gap junctions r connexin family
 6 connexins form a hemichannel / CONNEXON
 CONNEXON of two adjacent cells form the communication pathway b
tn two adjacent cells
 These allows the passage of small metabolites, second messenger, ions
Therefore it connects the cells both electrically & chemically.
 supporting cells causes the removal of excess K+ ions from the intercell
ular spaces of the sensory epithelium during hair cell repolarization
 2 connexin isoforms cx26,cx30

36. Cx26 & cx30 mutation-->hereditary SNHL
CX26 mutation-->most common cause of non syndro
mic hereditary deafness
CX26 is important for development of organ of corti
Connexin mutations has less effect on vestibular
system

37. VESTIBULAR SYSTEM
divided into two parts:
• saccule is anatomically & developmentally a separate chamber
from the utricle and semicircular canals
• In the evolutionarily most primitive vertebrates (e.g. hag fish), the
inner ear is composed of only two semicircular canals with a single
utricle-like chamber with a macula.
• During ontogenetic development, the utricle and semicircular canals
arise on one side of the embryonic otic vesicle, opposite to that
saccule & cochlea develops
This is the basis of noise induced vertigo in Tullio phenomenon

39. Sensory epithelia of vestibular cells:
 The maculae of the utricle and saccule are flat sheets of
epithelium that are oriented at right angles to each other
In utricle-->anterior–posterior plane,U-shaped
In saccule-->superior-inferior plane,almost S-shaped
 The cristae ampullaris of semicircular canals r saddle shape
 Nerve cell bodies that innervate these cells r collected together
in scarpa's ganglion/ vestibular ganglion

40. Extracellular matrix of vestibular system
 Otoconial membrane of utricle,saccule
 Cupula over the cristae of scc
Otoconial membrane consists of a large number of otoconia (eardust)
Structure of otoconia:It is a crystal,has proteinaceous core surrounded
by caco3 crystals that is present on the honey comb like perforated
sheet of non collagenous fibrillation extra cellular matrix

42. Protein core of otoconial membrane is made up of
Otoglein
α- and β-tectorins
ceacam 16 (carcinoembryonic antigenrelated cell
adhesion molecule 16).
The utricular and saccular maculae detect translational motion
/linear motion of the head in the horizontal and vertical planes.
Proteinaceous component of cupula in scc
Otoglein only
The cristae detect rotational acceleration of the head.
In tectorial membrane of cochlea: otoglein, α- and β-tectorins, ceacam 16

43. Hair cell types in vestibular system:

44. Type 1 HC Type 2 HC
Flask shaped Cylindrical
Single large afferent N ending(calyx)
over basolateral surface of cell
Multiple bouton like afferent N
ending
Efferent N contact with afferent
calyx
Efferent N direct contact with hair
cells
Nucleus near base Nucleus close to luminal surface
Thick sterocilia. More actin Not so thick
High calretinin No calretinin

45. calcium-binding protein, which is not expressed in type 2 hair
cells
Immunolabelling of calretinin ,helps to diff type1 & type 2HC.
also provides information regarding the number & distribution
of Type 1 HC
calretinin,
Type 1 HC Type 2 HC
Striolar region of macula Extrastriolar region of macula
Crest of crista Skirts of cristae
Location

46. INNERVATION PATTERN OF HC
Individual afferent neurons usually branches to innervate more
than one hair cells
Neurons that innervate striolar region of macula & crest of cristae
form calyceal nerve endings with single T1 HC
Neurons in peripheral region form only bouton endings with several
T2 HC
But majority of Afferent r dimorphic i.e they innervate both T1 &
T2 HC

47. • Neurons innervating striolar region of maculae & crest of cupulae
doesn't cross over to extrastriolar region or skirts of cristae
Innervation in different regions of sensory epithelium r
anatomically separate.

48. Supporting cells of vestibular system
Less specialised than sc of organ of corti
Forms reticular lamina
Phagocytosis and removal of dead / dying hair cells

49. Ion transporting epithelium of vestibular system
Known as dark cells ,bcoz of the histological appearance
Present in utricle,scc. absent in saccule
Main function is regulation of k+ in endolymph
Basal surface has Na k ATPase pump& Na k 2cl cotranspo
rter pump.
Basolateral surface is exposed to perilymph .k+ is shunted
from perilymph to endolymph