anatomy of inner ear
TRANSCRIPT
Anatomy Of Inner EAR
Presenter-Dr.Razal M Sherif Moderator-Dr.Joythi Swarup.R
Questions in previous Presentation
Malleus o Weight-23mgo Length-9mm
Incus o Weight-25-30 mg o Length of long process -7 mmo Length along short process-5mm
Stapes o Weight-2.86 mgo Height-3.26 mm
Inner Ear/Labyrinth • Development of Inner ear starts by 3rd week of IUL and completes
by 16th week.
• Cochlea sufficiently developed by 20th week (fetus can hear in the womb)
• Lies in the petrous part of the temporal bone.
• Is an important organ of hearing and balance.
• 2 Parts• Bony Labyrinth• Membranous Labyrinth
Bony Labyrinth• Vestibule• Cochlea• Semicircular Canals
Vestibule• Small Ovoid bony chamber measuring 4mm• situated between
o Laterally - Medial wall of the middle ear • is the opening of the oval window which is closed by the
footplate of the stapes o medially - by Internal auditory meatus .
• Medially(inner Surface)-2 recesseso Spherical recesses-lodges the saculeo Elliptical recesses-lodges the utricle
• Below elliptical recesses-opening of endolymphatic duct
• Postero superioro 5 openings of SCC
Semi Circular Canals• 3 semi circular canals
o Superior o Posterioro Lateral
• They lie in planes at right angle to each other.• Each canal got ampullary end ,which open in the
vestibule.• Non-ampullary end of Lateral SCC open independently • Post. SCC and Sup. SCC form a common opening
Called CRUS COMMUNE
Cochlea• Coiled tube – 35mm.• Two and half turns around a central bone called
Modiolus
MODIOLUS • Pyramidal Shaped • Base directed towards Internal Acoustic Meatus
• Vessels and Nerves enter cochlea via modiolus• Around modiolus -thin plate of bone winding
spirally is a called – Osseous Spiral lamina
• The Osseous Spiral lamina divides the bony cochlea (incompletely) into o Scala Vestibuli o Scala Tympani.
• And gives attachment to a membrane called Basilar membrane.
• Above the Osseous Spiral lamina and the Basilar membrane lies the Scala Media which contains the endolymph and Organ of Cori.
• The 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 vestibulio closed by the foot plate of stapes
• scala tympani o Closed round window membrane (secondary tympanic
membrane)• Connected to Sub arachnoid space by aqueduct
of choclea
Membranous Labyrinth
• It lies within the bony labyrinth
• Filled with Endolymph.• Space between membranous
labyrinth and bony labyrinth-Perilymph.
• It containso Cochlear Ducto Utricle and Saccule(otolith organs)o Semi circular Ducto Endolymphatic Duct and Sac
Cochlear duct• It is a blind coiled tube.
o called as Scala Media/membranous cochlea
• It appears triangular on cross-section- o One wall of triangle is the basilar membraneo Another wall of triangle is the Reissner's membraneo And the third wall is the stria vascularis,
• Cochlear duct is connected to the saccule by Ductus reuniens
• Utricle o lies in the posterior part of bony vestibule. o It receives the five openings of the three semicircular ducts. o It is also connected to the saccule through utriculosaccular
duct. o sensory epithelium of the utricle is called the macula
• Sacculeo Lies anterior to urticle o sensory epithelium of the saccule is called the maculao Responds to linear acceleration and decelerationo In Meniere’s disease –distented saccule lies against stapes
foot plate
• Semicircular ducts. o three in number and correspond exactly to the three
bony canals. o They open in the utricle. o The ampullated end of each duct contains a thickened
ridge of neuroepithelium called crista ampullaris.
• . Endolymphatic duct and sac. o the union of two ducts, one each from the saccule and
the utricle. o It passes through the vestibular aqueduct. o Its terminal part is dilated to form ENDOLYMPHATIC SAC
which lies between the two layers of dura on the posterior surface of the petrous bone.
Fluid System• Perilymph
o Present in btw memb. Labyrinth and bony labyrintho Present in inside the scala vestibuli and Scala tympani o Rich in sodium (Na+)o Like extra cellular fluido It communicates with CSF through the aqueduct of
cochlea.o Formation of perilymph:
• It is a filtrate of blood serum and is formed by capillaries of the spiral ligament
• a direct continuation of CSF and reaches the labyrinth via aqueduct of cochlea.
• Endolympho fills the membranous labyrinth o resembles intracellular fluid, o rich in Potassium (K+) ions. o It is secreted by
• secretory cells of the stria vascularis of the cochlea • the dark cells (present in the utricle and the
ampullated ends of semicircular ducts) .
Composition of inner ear fluids
ORGAN OF CORTI• Organ of hearing,• Situated on basilar membrane of cochlea
• 3 partso Sensory Hair cellso Supporting cellso Tectorial Membrane
Hair Cells• Transduce sound energy to Electrical Energy.• 1 row of flask shaped inner hair cells • 3 or 4 rows of cylindrical shaped outer hair cells.• Situated around the tunnel of corti
Inner Hair cells Outer Hair cells
• Total No : 3500• Arranged in single row• Flask shaped• 95% afferent from
Cochlear nerve (8th CN)• Stereocilia arranged in
V or W format• More resistent• Transmit auditory
stimuli
• 12,000 [ 1:4 ratio]• Multiple rows• Cylindrical• Efferent from Sup.
Olivary complex• Stereo cilia single
continous layer.• Easily damaged to
drugs & loud sound• Modulate the IHC.
Supporting cells
• Stabilize and support the organ of corti• Supply nutrient to the highly specialized sensory
cells(inner and outer hair cells)• Includes
o Hensen's Cell o Claudius Cells o Deiters Cellso Boettcher’s Cell
Tectorial Membrane
• It over hangs the organ of corti• Gelatinous – Spread over the hair cells.• The shearing force between Hair cells and
Tectorial membrane produces the stimulus in hair cells.
Cristae Crista Ampullaris
• Seen in the ampullated end of 3 SCC
• thickened ridge - covered by a gelatinous matrix called Cupula
• Two type of hair cells• Type 1 – Flask shaped• Type 2 – Cylindrical
• The cilia of sensory hair cells are present in cupula.
Maculae• Located in otolith organs• Sense the position of Head in
response to gravity• Hair cells
• Type 1• Type 2
• Supporting cells
• Otolithic membrane• Gelatinous layer
• Otoconia [Ca(CO3)2]• Cilia of hair cells in gelatinous
layer – Senses linear, gravitational & head tilt movements.
•
Ant. Inferior Cerebellar Art
Labyrinthine/Internal Auditory
art.
Ant. Vestibular
A(to utricle &
LSCC, SSCC)
CommonCochlear
VestibuloCochlear
Main Cochlear80%
Cochlear branch(20%)
Post. Vestibular A
(to saccule & PSCC)
Blood SupplyArterial
Venous Drainage
• 3 Veinso Internal auditory veino Vein of cochlear aqueducto Veins from the vestibular aqueduct
Applied Anatomy Presbycusis
o Sensory hearing loss associated with physiological ageing process in ear.
o 4 Pathological type• Sensory-degenaration of organ of corti• Neural-degenartion of spiral ganglion• Straial-Atropy of stria vascuaris• Cochlear-Stiffing of Basilar membrane
Noise induced hearing losso Damages the Hair cell-outer hair cells are affected more
Ototoxicityo Damage inner ear and cause SNHL,Tinnitus and vertigo.o Aminoglycoside-destroy type-1 hair cell in crista Ampularis
and outer hair cells.o Diuretics-edema and cystic changes in stria Vascularis.o Quinine-causes vasoconstriction of small vessels of cochlea
and stria vascularis.o NSAIDs-Piroxicam,KetorolacMeniere’s disease(Endolymphatic Hydrops)o Endolymphatic distention mainly in scala media,saccule,Utricleo Leads to bulging of Reissner’s Membrane and saccule and
utricle.
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