1. Dr Vikas ANATOMY OF INNER EAR

2. Major Divisions of the Ear 3. Inner Ear Consists of an irregular system of canals and cavities: Bony labyrinth Membranous labyrinth 4. Bony labyrinth: Hard, bony outer shell. Membranous labyrinth: Fully contained inside the bony labyrinth . 5. Bony labyrinth Vestibule central chamber of labyrinth. In its lateral wall lies the oval window. Inside of its medial wall present two recess, a spherical recess lodges the saccule and an elliptical recess which lodges the utricle. Semicircular canals -The vestibule and semicircular canals are concerned with vestibular function (balance) Cochlea- The cochlea is concerned with hearing. 6. Parts of the Bony labrynth 7. Membraneous labrynth 8. Parts of the Membraneous labrynth Cochlear duct Utricle Saccule Three semicircular canals Endolymphatic duct and sac 9. Membranous labyrinth Within the cavity is the membranous labyrinth, with 2 sacs: A. Utricle B. Saccule C. 3 semicircular ducts from the utricle( anterior, Posterior, lateral) D. cochlear duct (bony spiral) Endolymph, fluid within the membranous labyrinth Perilymphatic space, separates the osseous from the membranous labyrinth Perilymph, fluid within the perilymphatic space. 10. Membranous labyrinth of the ear 11. Semicircular Canals Three semicircular canals- Lateral (Horizontal) Superior ( Anterior vertical) Posterior ( Posterior vertical) Each canal is 0.8 mm in diameter, has a ampullated limb measuring 2mm in diameter & a nonampullated limb which is 1mm in diameter. Occupies 2/3rd of a circle Ampulla is cribrosed for passage of nerve fibers Ampullated & nonampullated limbs all open into the vestibule The non ampullated ends of posterior and superior canals join & form Crus Commune (4 mm length) it opens into medial part of vestibule. So three SCC opens into vestibule by 5 openings. 12. Semicircular Canals The angle formed by three semicircular canals is the Solid angle. 13. Trautmanns triangle. The triangle bounded by the bony labyrinth, sigmoid sinus, and superior petrosal sinus is known as Trautmanns triangle. 14. This triangle is a potential weak spot through which infections of temporal bone may traverse and affect cerebellum. Extra dural abscess involving the posterior cranial fossa is also possible when thin bone in this triangle gets breached in infections / cholesteatoma involving mastoid cavity. Since bone in this area is rather thin it can be drilled out to enter into the posterior cranial fossa. This can be used as an approach to posterior cranial fossa lesions. The size of this triangle is highly variable depending on the size of the sigmoid sinus. A large sigmoid sinus reduces the size of this triangle and also increases the angulation of the superior petrosal sinus with it. This impedes the venous drainage predisposing to the development of endolymphatic hydrops. 15. Horizontal semicircular canal The lateral or horizontal canal (external semicircular canal) is the shortest of the three canals. Movement of fluid within this canal corresponds to rotation of the head around a vertical axis (i.e. the neck). Projects as rounded bulge in middle ear, aditus & antrum. Makes an angle of 30 with horizontal plane. It measures from 12 to 15 mm., and its arch is directed horizontally backward and laterally; thus each semicircular canal stands at right angles to the other two. Its ampullated end corresponds to the upper and lateral angle of the vestibule, just above the fenestra vestibuli, where it opens close to the ampullated end of the superior canal; its opposite end opens at the upper and back part of the vestibule. The lateral canal of one ear is very nearly in the same plane as that of the other; while the superior canal of one ear is nearly parallel to the posterior canal of the other. 16. Superior semicircular canal The superior semicircular canal (anterior semicircular canal) detects rotation of the head around a rostral- caudal (anterior-posterior) axis, or in other words rotation in the coronal plane. This occurs, for example, when you move your head to touch your shoulders. It is 15 to 20 mm in length, is vertical in direction, and is placed transversely to the long axis of the petrous portion of the temporal bone, on the anterior surface of which its arch forms a round projection. Its lateral extremity is ampullated, and opens into the upper part of the vestibule; the opposite end joins with the upper part of the posterior canal to form the crus commune, which opens into the upper and medial part of the vestibule. 17. Posterior semicircular canal The posterior semicircular canal detects rotations of the head in around the lateral axis. This occurs, for example, when nodding your head. It is directed superiorly, as per its nomenclature, and posteriorly, nearly parallel to the posterior surface of the petrous bone. The vestibular canaliculus is immediately medial it. It detects rotations of the head in the sagittal plane. It is the longest of the three canals, measuring from 18 to 22 mm. Its lower or ampullated end opens into the lower & back part of the vestibule, and upper end into the crus commune. 18. Semicircular Canals Each membranous semicircular canal is filled with endolymph, a potassium-rich extracellular fluid, and is bathed in perilymph, which has the approximate composition of cerebrospinal fluid. Ampulla, which contains the crista ampullaris and cupula. The crista ampullaris is a saddle-shaped gelatinous structure along one wall of the membranous canal that contains hair cells, the sensory cells of the vestibular system. The cupula acts as a membranous diaphragm, stretching from the crista to the opposite walls of the canal. Crista and cupula in each ampulla sense angular acceleration 19. The attachment of the cupula, which extends from the apex of the crista to the opposite wall of the membranous ampulla. Arrowheads indicate subcupular space. 20. Vestibule Central chamber of labrynth (5 mm) Lateral wall contains oval window(fenestra vestibuli) closed by footplate of stapes sorrounded by annular ligament. 21. Otolithorgans The utricle and saccule, together called the otolithorgans, also contain hair cells that bend in response to acceleration of the head. Instead of cristae, however, the sensory epithelium of these organs is covered by flat, kidney-shaped sheets called maculae. 22. One macula is applied horizontally to the ceiling of the utricle, whereas the other hangs sagittally on the wall of the saccule. Each macula is a gelatinous matrix into which hair cells project and which is studded with tiny calcium carbonate granules called otoconia. 23. Whereas the cristae have a specific gravity identical to the surrounding endolymph, the otoconia increase the density of the maculae and render them sensitive to shearing forces parallel to their surfaces caused by gravity or linear motions of the head. Any time the head moves linearly, the heavy maculae lag behind, bending the hair cells embedded in them. The utricle primarily senses lateral tilt and translation of the head, whereas the saccule measures front-to-back tilt and translation as well as motion aligned with the pull of gravity. 24. Hair cells located in the sensory epithelia of the semicircular canals and otolith organs are responsible for transforming motion into a modulation in the discharge rate of afferent nerve fibers innervating the vestibular nerve. 25. Utricle Walls are composed of: a. outer fibrous layer b. intermediate delicate vascular connective tissue c. inner squamous to low cuboidal except in specialized receptor regions that are columnar and more complex. 26. Saccule Endolymphatic duct = small ducts from utricle & saccule, Lined by squamous to cuboidal epithelium up to membranous labyrinth, near end it is transitional to tall columnar cells. Endolymphatic sac is active site for absorption of endolymph. Dark cells Large irregular shaped nucleus, smooth free surface. Cell base has shallow infoldings of the membrane. Light cells free surface has profuse long microvilli, numerous micropinocytotic invagination of membrane. With clear vacoules in apical cytoplasm Plasma membrane at cell base is smooth Lateral membrane is extensively interdigitate with neighboring cells. Specialized for absorption. 27. utricle Oblong and irregular Has anteriorly upward slope at an apparent angle of 30 It lies in posterior part of bony vestibule & recieves the five openings of three SCC Utricle(4.33 mm) is bigger than saccule (2.4 mm) & lies superior to saccule Utricle connected to saccule via utriculosaccular duct Its sensory organ macula is concerned with 28. Utricle Dark and light cells are distinguishable in unspecialized regions of the epithelium. Dark cells have highly irregular nuclei outline, located near the apical surface apical cytoplasm contains coated vesicles, larger smooth vesicles, occasional lipid droplets. Basal cytoplasm with long mitochondria. Function =Responsible for ionic composition of the endolymph. Light cells have sparse microvilli on apical surface, occasional micropinocytosis vesicles. Cytoplasm has small numbers of ribosomes & few mitochondria. Function = Ion transporting cells. 29. Macula Utriculae Found in the floor of the utricle, a thick special sensory epithelium,with hair cells & supporting cells. The kinocilium & stereocilia of the hair cells project into the underside of the Otolithic membrane Otoliths (otoconia) = minute 3-5um crystalline bodies of protein & calcium carbonate embedded in Otolithic membrane. 30. Endolymphatic duct and sac Ducts from utricle and saccule unites and form utriculosaccular duct Continues as endolymphatic duct that passes via the vestibular aqueduct 31. saccule lies anterior to utricle opposite the stapes footplate in the bony vestibule. its sensory organ macula is concerned with linear acceleration & decelaration. Saccule is connected to the cochlea via a thin reunion duct. 32. Saccule Macula of saccule - ovoid thickening of the wall of the anterior globular saccule. Found in the vertical anterior wall, hair cells responds to movements at right angle & activate the macula of utricle which is in horizontal position when head is in upright position, providing info to brain regarding head position as to pull of gravity. Ductus utriculosaccularis - communication between utricle to saccule. Ductus reuniens - short tube that runs from the saccule to basal end of cochlear duct. 33. Saccule Endolymphatic duct - small ducts from utricle & saccule, Lined by squamous to cuboidal epithelium up to membranous labyrinth, near end it is transitional to tall columnar cells. Endolymphatic sac is active site for absorption of endolymph. Dark cells Large irregular shaped nucleus, smooth free surface. Cell base has shallow infoldings of the membrane. Light cells free surface has profuse long microvilli, numerous micropinocytotic invagination of membrane. With clear vacoules in apical cytoplasm Plasma membrane at cell base is smooth Lateral membrane is extensively interdigitate with neighboring cells. Specialized for absorption. 34. Membranous labyrinth with the entire bony labyrinth stripped away. 35. The Cochlea Snail shaped coiled tube 2.5 to 2.75 turns round a central pyramid of bone called modiolus. 30 mm long 5 mm from base to apex & 9 mm around its base Anterio medial to vestibule. 36. Modiolus ? Central pyramid of bone around which cochlea forms The base of modiolus directed towards internal acoustic meatus Transmits vessels and nerves to cochlea Apex lies medial to tensor tympani muscle 37. Spiral lamina = spiral ledge from modiolus to cochlear canal. Basilar membrane = thin sheet extending from spiral lamina to spiral ligament of cochlea. Movement of the the basilar membrane by pressure changes induced by stapes footplate motion at the oval window is a critical step in the transduction process. Vestibular membrane = 2nd partition from soft tissue ridge of spiral lamina to the spiral ligament. Reissners membrane = outer surface of vestibular membrane, lined by thin squamous perilymphatic cells. Lumen of cochlear canal is partitioned into 3 spiral chambers: 1. scala vestibuli (above) 2. scala tympani (below) 38. Osseous spiral lamina ? A thin plate of bone winds spirally around modiolus like the thread of a screw . This bony lamina gives attachment to the basilar membrane and divides the bony cochlea tube into three compartments. 1. Scala vestibuli 2. Scala tympani 3. Scala media (membraneous cochlea) 39. Rosenthals canal ? Spiral ganglions are situated in this canal which runs along the osseous spiral lamina. 40. The cochlea uncoiled Movement of the the basilar membrane by pressure changes induced by stapes footplate motion at the oval window is a critical step in the transduction process 41. Scala vestibuli ? This uppermost channel is continuous with vestibule and closed at oval window by stapes footplate 42. Scala tympani ? This lowermost channel is closed by secondary TM of round window 43. Scala media ? Bind coiled tube, connected to the saccule via ductus reunions. 44. Aqueduct of cochlea? A bony bulge in the medial wall of middle ear , represents the basal coil of cochlea. Promontory ? Scala tympani is connected with subarachnoid space via aqueduct of cochlea. It is thought to regulate perilymph & pressure in bony labrynth. 45. Cochlear duct 46. Cochlear duct-relations & boundaries 1. Basilar membrane base It supports organ of corti 2. Reissners membrane Seperates scala media from scala vestibuli 3. Stria vascularis It contains vascular epithelium and secretes endolymph 47. Scala media is more or less triangular, formed by Reissners membrane, basilar membrane and the structure called the stria vascularis. The fluid that fills scala tympani and scala vestibuli is called perilymph; the fluid that fills scala media is called endolymph. The organ of Corti rests on the basilar membrane within scala media. 48. Spiral limbus Limbus = A bulging of the osseous spiral lamina into the scala media. The inner angle convergence of the vestibular membrane and basilar membrane. Internal spinal sulcus = a tapering upper edge projecting laterally over the recess of internal spinal sulcus( tunnel). Auditory teeth = vertically oriented collagen fiber bundles within the limbus. Interdental teeth = uniformly spaced along the upper surface of the limbus between auditory teeth, secretes the Tectorial membrane. 49. Tectorial membrane Secreted at the upper surface of interdental cells, forms a cuticular layer over these cells Composed of fine filaments embedded in gelatinous matrix rich in mucopolysaccharides. Fibers consists of a protein similar to epidermal keratin. 50. Basilar membrane Extends across the cochlear canal from spiral lamina to the spiral ligament. Separates the scala media from the scala tympani Supports the Organ of Corti 0.25 mm across x 35 m long from base of cochlea to apex. Has 2 zones: Zona arcuata = thin, extends from medial attachment to base of outer most cells of organ of Corti. Supports the organ of Corti, with radially oriented 10 nm collagen like fibrils. Zona pectinata= thicker from organ of Corti to spiral ligament. Trilaminar in structure. Upper layer is meshwork of transverse fibers. Lower layer is of longitudinal fibers. In between is structureless intermediate layer of few fibroblasts like cells. * The width of fibers vary from 0.20 mm to 0.36 mm at the apex, the diameter of component fibers gradually decreases vibrate at higher frequency near base and lower frequency near the Helicotrema, thereby 51. Notice the stria vascularis (also area vascularis) The s.v. secretes endolymph. Notice also the spiral ligament, which attaches the b.m. to the bony wall of the cochlea, and the limbus (or limbus spiralis), a fibrous covering of the spiral lamina. modiolus spiral ligament 52. Cross-section of the cochlear duct 53. Inner ear fluids perilymph between bony and membraneous labrynth Endolymph fills the entire membraneous labrynth perilymph endolymph Resembles ECF Resembles ICF Rich in sodium ions Rich in pottasium ions 54. The terminal part of the endolymphatic duct is dilated and forms endolymphatic sac , which is situated between two layers of dura on the posterior surface of petrous bone. 55. Organ Of Corti The end organ of hearing Inner pillar cells - broad base, resting on the basilar membrane, slender and conical, nucleus is basal. Inner tunnel - wide triangular intercellular space continuous thru cochlear length. Bounded above converging inner and outer pillar cells, Outer pillar cells -longer and more oblique, leaning to the inner pillars.with broad thin base. Deiters cells -the supporting cells for the 3 -4 rows of outer hair cells. Base is columnar with cup shaped upper end. The apex does not reach the free surface of the organ of Corti. 56. Inner phalangeal cells - arranged in a row on the inner side of the inner pillar cells. Contiguous with slender Border cells marking the inner boundary of the organ of corti. Lining epithelium is low cuboidal or squamous cells. Cells of Hensen - delimit the outer border of the organ of Corti arrange in rows decreasing in height continuous with the cells of Claudius. 2 types of hair cells in cochlea: A. inner hair cells - like type 1 hair cells, single row along the entire length of the cochlea. B. Outer hair cells - 3 rows between pillar cells and outer phalangeal cells 57. Two types of cells in the organ of Corti are support cells and hair cells. The hair cells are the receptor cells-- the ones that transduce sound. Support cells such as the Deiters cells support hair cells. The tops of the hair cells and pillar cells form the reticular lamina, which isolates the hair cells stereocilia from their cell bodies. The tectorial membrane is loosely coupled to the reticular lamina. There are 4 rows of hair cells, One row on the inner (modiolar) side of the tunnel formed by the pillar cells-- these are the inner hair cells 3 row on the outer side of the Tunnel of Corti, these are the outer hair cells. Deiters cells support the Outer hair cells at their base, but 58. A closer look at the organ of Corti 59. Reticular lamina 60. Deiters cells 61. Arrangement of hair cells 62. Stereocilia 63. Arrangement of stereocilia 64. Cochlea The cochlea contains an array of highly specialized cells arranged in a highly specialized manner. There are structural differences between IHCs and OHCs that suggest that they differ in function The cochlea not only sends a message to the brain, but it may also receive messages from the brain via efferent innervation. 65. Innervation of the organ of Corti Nerve fibers 66. The spiral ganglion The cell bodies of the neurons that form the auditory nerve are located within the cochlear modiolus. The collection of cell bodies is called the spiral ganglion. 67. Pattern of afferent innervation Different types of nerve fibers innervate IHCs and OHCs. Type I fibers innervate IHCs Type II neurons innervate OHCs. 68. Pattern of afferent innervation Nearly all of the nerve fibers that carry messages from the ear to the brain innervate inner hair cells. Each IHC has its own private set of fibers. The Type II nerve fibers innervate many OHCs. and the OHCs they innervate are basal to the point at which the nerve fiber enters the cochlea. 69. Thin fibers attach toward modiolar side, thick fibers toward outer side of IHC. 70. Pattern of efferent innervation Neurons from the brainstem also contact hair cells. These neurons carry information from the brain to the ear and are called efferent neurons. The vast majority of efferents innervate OHCs, and the contacts on OHCs differ from those on IHCs. Efferents form large calyx-shaped contacts on the OHC cell body; efferents form small bouton-like contacts on the afferent nerve fibers that contact IHCs. 71. Pattern of efferent innervation 72. Blood supply of labrynth Mainly by internal auditory artery (branch of Ant. Inf. Cerebellar Aartery