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Inner ear anatomy

presentation about anatomy of inner ear.

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Inner ear anatomy

  3. 3. EMBRYOLOGY OF INNER EAR  Initially membranous labyrinth is formed followed by encasement by bony labyrinth.  Involves 3 main stages: 1. Development (4th-8th week) 2. Growth (8th to 16th week) 3. Ossification (16th to 24th week)
  4. 4. DEVELOPMENT OF INNER EAR  The membranous labyrinth is derived from a specialized of surface ectoderm overlying developing HINDBRAIN.  This area of thickening is known as OTIC PLACODE.  Soon it depresses below the ectoderm to form OTIC PIT.  The pit becomes rounded to form OTIC VESICLE which separates from surface ectoderm.
  5. 5.  The otic vesicle is an oval structure in the beginning.  By differential growth of its various parts of its wall, it gives rise to structures comprising MEMBRANOUS LABYRINTH.
  6. 6.  Localized areas of epithelium of the membranous labyrinth undergo differentiation to form specialized sensory end organs of hearing and equilibrium: 1. Cristae of SCC 2. Maculae of utricle & saccule 3. Organ of Corti of cochlea.  They are innervated by peripheral process of vestibulocochlear ganglion ( derived from neural crest)
  7. 7. DEVELOPMENT OF ORGAN OF CORTI  Initially, epithelial cells of cochlear duct are alike.  They form two ridges :  Inner ridge  Outer ridge- forms one row of inner hair cells or 3-4 rows of outer hair cells.  Hair cells are the sensory cells of auditory system.  Tectorial membrane : a fibrilar gelatinous substance attached to the spiral limbus that rest with its tip on the hair cells.  The sensory cells + Tectorial membrane = Organ of Corti.
  8. 8.  The BONY LABYRINTH is formed by the mesenchyme surrounding the membranous labyrinth.  This mesenchyme thus becomes condensed k/a OTIC CAPSULE.  This condensation is soon converted into cartilage.  b/w the cartilage & membranous labyrinth there is a layer of loose PERIOTIC TISSUE.  This periotic tissue disappears to create the space of bony labyrinth and gets filled up by PERILYMPH & the membranous one gets filled with ENDOLYMPH.
  9. 9.  The periotic tissue around the utricle and saccule also disappears to form a space k/a VESTIBULE.  They also disappears around the SC DUCTS to form SCC forming to distinct spaces around the cochlear duct on either side k/a S. TYMPANI & S.VESTIBULI.  The S. VESTIBULI communicated with the vestibule while the S.TYMPANI grows towards the TYMPANIC CAVITY from which it remains separated by a membrane  The cartilaginous labyrinth subsequently ossifies to form bony labyrinth.
  10. 10. LABYRINTH  Hard & outer bony shell  It consists of a) Vestibule (utricle & saccule) b) Semicircular canal c) Cochlea  Gap between osseus and membranous is filled with perilymph (similar to ECF)  Placed inside bony labyrinth  It consists of : a) Vestibular apparatus b) Cochlear duct o This is filled with endolymph (similar to cytosol) OSSEOUS (BONY) MEMBRANOUS
  11. 11. VESTIBULE  It is the central part of the bony labyrinth.  It lies medial to the middle ear cavity & its lateral wall opens into m.ear at the fenestra vestibuli which is closed by stapes footplate.  Ovoid in shape but flattened transversely (5mm*3mm).  SPHERICAL RECESS :present on medial wall contains saccule perforated by many minutes holes (macula cribosa media) transmitting fine branches of vestibular nerve.  VESTIBULAR CREST : present behind the recess. The anterior end forms the vestibular pyramid. This divides to below to enclose COCHLEAR RECESS.  ELLIPTICAL RECESS: post sup to vestibular crest in the roof and the medial wall of vestibule containing utricle.  The vestibular aqueduct opens below the elliptical recess.  In the post part of the vestibule are the 5 openings of the scc and the anterior part leads in the scala vestibuli of cochlea.
  12. 12. SEMICIRCULAR CANALS  There are 3 semicircular canals : (a) Anterior (b)posterior (c) lateral  They all are compressed side to side and each forms approx 2/3 rd of a circle.  They all are unequal in length but similar in diameter i.e. 0.8mm except at the AMPULLA which is twice the diameter.  Lie in plane at right angles.  Each have two ends ampullated and non ampulated  All three ampulated ends and the non ampulated end of lateral SCC open independently into the vestibule.  The non ampulated end of anterior and posterior joins to form crus commune (4mm long opening into medial part of vestibule)  Superior scc is situated transverse to the axis of pterous part of temporal bone.
  13. 13. COCHLEA  Derived from greek word (cochlos for snail)  5mm from base to apex & 9mm around its base  2.5 to 2.75 turns around a central pyramid of bone = MODIOLOUS.  The base of MODIOLUS is directed towards IAM & transmits nerves to cochlea.  PROMONTORY =Basal turn of cochlea produces a bulge in medial wall of middle ear
  14. 14.  Thin plate of bone winding spirally around MODIOLUS like a thread of screw k/a BONY SPIRAL LAMINA.  ROSENTHAL’S CANAL: spiral ganglion are situated in this canal which runs along the osseous spiral lamina
  15. 15.  Bony cochlea is divivded into : 1. SCALA VESTIBULI : closed by stapes footplate and contains perilymph 2. SCALA TYMPANI : closed by secondary TM & contains perilymph. Connected to sub archanoid space through Aqueduct of cochlea. 3. SCALA MEDIA : also known as COCHLEAR DUCT & contains endolymph.
  16. 16.  Scala vestibuli & scala tympani connects to each other at the apex of cochlea HELICOTREMA.
  17. 17. COCHLEAR DUCT  It is a blind coiled tube & made up of 3 walls : 1. BASILAR MEMBRANE 2. REISSINERS MEMBRANE 3. STRIA VASCULARIS
  18. 18. ORGAN OF CORTI  Discovered by Alfonso Giacomo Gaspare Corti.  Components of organ of Corti :  Hair cells : imp receptor of hearing & transduce sound energy into electrical energy Inner hair cells Single row Richly supplied by afferent cochlear fibers & are more important in transmision of auditory impulse Outer hair cells Arranged in 3-4 layers Mainly receives efferent innervation from olivary complex & are connected with modulating the function of inner hair cells.
  19. 19.  TUNNEL OF CORTI : Formed by inner & outer rods & contains fluid called as Cortilymph.  SUPPORTING CELLS : Dieters cells &cells of hansen.  TECTORIAL MEMBRANE : contains gelatinous matrix with delicate fibers. The shearing force btw the hair cells & tectorial membrane produces stimulus to hair cells.
  20. 20. UTRICLE & SACCULE  Utricle lies in the posterior part of the bony vestibule & receives the 5 openings of scc  Connected to Saccule via Utricosaccular duct  The macula of the utricle lies mainly in the horizontal plane on the inferior surface of the utricle and plays an important role in determining orientation of head when the head is upright (force like gravity)  The Macula of the SACCULE is located mainly in a vertical plane & signals head orientation when the person is lying down.
  21. 21.  The epithelial surface of each macula is characterized by hair cells with numerous stercocilia & one prominent kinocilum. These cells are covered by gelatinous structure known as OTOLITHIC or statoconial membrane and embedded in it are several small crystals k/a otoconia (linear acc of head will cause the otolithic memb to lag behind as a result of inertia produced by its increased density & will lead to activation or inhibition of the mechanosesitive hair cells)
  22. 22. COMPOSITION OF INNER EAR FLUID PERILYMPH ENDOLYMPH PRESENT IN SCALA VESTIBULI SCALA TYMPANI SCALA MEDIA (membranous labyrinth ) PRODUCTION SLIGHT DIFFERENCES IN S.VESTIBULI – Plasma via endothelial boundary of cochlear blood vessels. In S. TYMPANI – derived from SUB ARACHNOID SPACE via cochlear canaliculus. Marginal cells of stria vascularis & dark cell of vestibule ABSORPTION : ENDOLYMPHATIC SAC K+ 5mM 150mM Na+ 150mM 2mM Cl- 120mM 130mM Ca+ 1.5mM 20uM PROTEIN 200-400 mg/dl 126 mg/dl The high potassium is important for mechanosensory hair cell function. GLUCOSE 85mg/dl 10-40 mg/dl
  23. 23. ENDOLYMPHATIC DUCT & SAC  Formed by the union of two ducts one forms the utricle & another from the saccule.  Passes through the vestibular aqueduct  Terminal part is dilated to form Endolymphatic sac.
  24. 24. FUNCTIONAL ANATOMY OF COCHLEA  Basilar membrane is a fibrous membrane.  Made up of 20-30 thousand basilar fibers.  Length of basilar membrane increases from base 0.04mm to apex 0.5mm but diameter decreases leading to 100 fold decrease of overall stiffness.
  25. 25. FUNCTIONAL ANATOMY CONTINUED.. Sound wave entering the oval window causes BM at the base of cochlea to move in direction of round window However due to elastic tension built in BM initiates a fluid wave that travel along the BM which travel towards the Helicotrema Each wave is weak at the onset but becomes stronger when it reaches that portion of the BM that has a resonant frequency equal to the respective sound frequency. ORGAN OF CORTI generates the nerve impulse in respponse to vibration of BM (which is mainly transmitted by inner hair cells) Excitation of the hair cells : stercocilia project upward from the hair cells & either touch or are embedded in the surface gel coating of tectorial membrane. Bending in one direction causes depolarization & in other causes hyper polarization.
  26. 26. INTERNAL ACOUSTIC MEATUS  About 1 cm longand passes into the petrous part of temporal bone in a lateral direction.  IAM is separated from the internal ear by a vertical plate divided by a transverse (Falciform) crest.  5 nerves pass through openings in vertical plate above and below the transverse crest:  Facial & sup vestibular nerve : superior to the crest. Facial lies anterior to the sup vestibular nerve and is seprated by bills barr (vertical ridge). The sup vestibular area also contains nerve to utricle , ant & lat scc.  The nervus intermedius lies between facial motor root and the sup vest nerve to which it may be adherent.  Cocohlear nerve and inferior vestibular nerve. Inferior vestibular area also contains opening for saccular nerves and a single hole k/a FORAMEN SINGULARAE which tranmits nerve to post scc.
  27. 27. VASCULAR SUPPLY : ANTERIOR INFERIOR CEREBELLAR ARTERY Labyrinthine artery Common cochlear Vestibulo cochlear Cochlear branch (20%) Post vestibular artery. (SACCULE & POST CANAL Main cochlear artery (COCHLEAR 80%) Antreior vestibular artery. (UTRICLE & LAT & SUP CANAL) Divides at IAM
  28. 28. VENOUS DRAINAGE  Veins draining the VESTIBULE and SCC accompany the arteries.  Internal auditory vein  Vein of cochlear aqueduct  Vein of vestibular aqueduct drain into inferior petrosal & sigmoid sinus
  29. 29. INNERVATION  The vestibulocochlear (8th ) provides special sensory innervations to the inner ear  After leaving IAM it divides into Cochlear Vestibular Spirals towards cochlea where it give branches throughout the coils of canal It again divides into superior & inferior with their own vestibular ganglion. Fibers then branch off & form spiral ganglia of corti in the modiolus of cochlea Superior ganglion fibers innervate ampulla of ant & lateral scc & the utricle Nerve fibers of these ganglia travel through the osseous spiral lamina & their dendrites communicate with stercocilia of organ of corti Inferior ganglion fibers supply ampulla of the post & saccule
  30. 30. REFRENCE  Greys anatomy -41st edition  B.D chaurasiya  Dhingra’s – disease of ent  Wikipedia
  31. 31. THANK YOU !