Labyrinths contain

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Labyrinths contain

• Three parts
• Semicircular canals
• Vestibular
  system
• Vestibule
• Cochlea Auditory system

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Vestibular system

• Function Balance and equilibrium
• Sensory cells Hair cells

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Auditory system Cochlea

• Name derived from snail-like shape
• Tube of decreasing diameter coiled around itself
• Coiled around a central bony canal called
  modiolus
• Broad base, narrow apex
• Length About 35 mm
• In human beings 2 and 5/8 coils

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Isolated cochlear turns from the inner ear of
fetal sheep Photo courtesy of Gerhardt, K.
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Cochlear macrostructure

• Partially divided throughout its length by a thin
  spiral shelf of bone called osseous spiral lamina
• At the outer (lateral) wall of the cochlea
  Spiral ligament

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• Between the osseous spiral lamina and the spiral
  ligament Basilar membrane
• Runs all the way along the length of the cochlea,
  except for a small opening at the apex called the
  helicotrema
• Reissners membrane projects diagonally from
  spiral lamina to outer bony wall of cochlea
• Joins the basilar membrane at the helicotrema

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• Between the osseous spiral lamina and the spiral
  ligament Basilar membrane
• Runs all the way along the length of the cochlea,
  except for a small opening at the apex called the
  helicotrema
• Reissners membrane projects diagonally from
  spiral lamina to outer bony wall of cochlea
• Joins the basilar membrane at the helicotrema

http//www.iurc.montp.inserm.fr/cric/audition/engl
ish/ear/fear.htm
http//epl.meei.harvard.edu/hwang/3Dviewer/3Dview
er.html
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Cross-section of the cochlea

• Basilar membrane and Reissners membrane divide
  the cochlear canal into three ducts
• Scala vestibuli
• Scala tympani
• Scala media

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Scala Vestibuli

• Above Reissners membrane
• Extends from oval window in the vestibule to the
  helicotrema
• Contains perilymph

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Scala Tympani

• Below the basilar membrane
• Extends from round window to the helicotrema
• Contains perilymph

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Scala media/cochlear sac

• Bound below by basilar membrane
• Bound above by Reissners membrane
• Bound on the outer side by Stria vascularis
• Contains endolymph

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Dimensions of the cochlear partitions

• Cochlea Narrower toward the apex
• Basilar membrane Narrower at the base and wider
  toward the apical end
• Apical end Flaccid and under no tension
• Base end Stiff and under a small amount of
  tension

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Cochlear microstructure

• Organ of Corti
• Lies on the basilar membrane in the scala media
• Contains many different types of specialized cells

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Organ of Corti
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Pillar cells or rods of Corti

• Provide structure and support
• Inner and outer pillar cells
• Form a tunnel called tunnel of Corti
• Contains fluid called cortilymph

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Hair cells

• On the outer side of the outer pillar/rod cells
  Outer hair cells (OHC)
• (Away from modiolus)
• On the inner side of the inner pillar/rod cells
  Inner hair cells (IHC)
• (Toward the modiolus)

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Supporting cells

• OHC supported by cells of Deiter and Hensen
• IHC supported by border cells of the inner sulcus

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Reticular lamina

• Formed partly by the phalangeal processes of the
  Deiters cells.

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OHC

• Around 12000 in number
• Test-tube shaped
• Three-five rows

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IHC

• Around 3400 in number
• Flask shaped
• Single row

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Stereocilia

• Hairlike projections
• Project from the top of IHC and OHC
• Graded in length
• Have cross-bridges called tip-links

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Stereocilia of OHC and IHC

• OHC
• 6-7 rows per OHC
• Each row has a W shaped arrangement
• IHC
• 2-4 rows per IHC
• Each row in a shallow U-shaped arrangement

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Tectorial membrane

• Gelatinous transparent membrane projecting from
  spiral lamina
• Attaches loosely on outer edge to the Deiters
  and Hensens cells.
• Longest stereocilia of OHC embedded in inferior
  surface of tectorial membrane
• Stereocilia of IHC not embedded in tectorial
  membrane

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