19. ear
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  • 1. Ear
  • 2. - The external ear consists of the auricle and the external acoustic meatus. Sound waves in the air are transmitted to the eardrum of the middle ear. - The middle ear starts from the tympanic membrane, the epitympanic recess, and the ossicles – malleus, incus, and stapes. The ossicles sense the vibrations of the sound waves on the tympanic membrane, converting and amplifying the energy into mechanical energy, which travels into the inner ear. Note the auditory, or Eustachian, tube connecting the middle ear to the nasopharynx, which allows the equilibration of pressure. - The inner ear consists of 1) the cochlea for auditory sense and 2) the semicircular ducts, ampullae, utricle, and saccule for the sense of balance and position. The membranous labyrinth is found within the bony labyrinth.
  • 3. - Note the handle, or manubrium, of the malleus (commonly known as the hammer) firmly attaches to the upper half of the tympanic membrane. The head of the malleus contacts the incus. - The incus, or anvil, body articulates with the head of the malleus. The long process or limb of the incus descends vertically, parallel to the handle of the malleus, and contacts the stapes. - The stapes, or commonly known as the stirrup, head articulates with the incus. The two crura or limbs diverge and join at the flattened oval base, which attaches to the oval window. - Via the three ossicles, vibrations are transmitted from the tympanic membrane to the oval window and to the inner ear, which will be discussed later. - Note the other structures within the tympanic cavity of the middle ear. The tensor tympani muscle inserts into the handle of the malleus and dampens vibrations of the tympanic membrane. - The stapedius muscle may not be visible, but its tendon attaching to the stapes may be seen. It acts to dampen vibrations of the stapes. - Note the facial nerve (CN VII) within the facial canal, making an almost 90 degree turn to exit the stylomastoid foramen. It gives off the greater petrosal nerve from the geniculate ganglion. Note also the chorda tympani coming off the facial nerve and traveling between the long limb of the incus and malleus handle.
  • 4. - Shown here is the view of the tympanic membrane through an otoscope. Note most of the eardrum has a strong fibrous layer that provides rigidity; this area is called the pars tensa. The upper one-sixth of the tympanic membrane lacks this fibrous layer and is termed the pars flaccida. The manubrium of the malleus attaches firmly on the tympanic membrane and can be seen. The cone of light from the otoscope can be seen inferior and anterior to the manubrium. Together, they look like an arm bending at the elbow. - As mentioned before, the inner ear specializes in auditory sense and sense of balance and equilibrium. - The cochlear nerve provides auditory sense from the cochlea, the spiral-shaped organ that receives the vibrations from the oval window and converts them to nerve impulses. - The vestibular nerve receives input from the semicircular ducts, the utricle, and the saccule. The semicircular ducts detect angular acceleration. The utricle and saccule detect linear acceleration. - The cochlear and vestibular nerves join together as CN VIII, the vestibulocochlear nerve. - Note once again the facial nerve (CN VII) traveling in close proximity to CN VIII and making a sharp bend near the tympanic cavity. Note also the geniculate ganglion, the greater petrosal nerve, and the chorda tympani.
  • 5. -The inner ear is located in the petrous part of the temporal bone. Both the tympanic cavity and bony labyrinth are found here. Within the bony labyrinth is the membranous labyrinth. - The bony labyrinth contains perilymph (high Na+, low K+), while the membranous labyrinth has endolymph (high K+, low Na+). - The inner ear is composed of the following: - semicircular ducts (anterior, posterior, and lateral) with associated ampullae - the utricle - the saccule - the cochlea - Review: The tympanic membrane transmits vibrations through the ossicles to the oval window. The vibrations then enter the inner ear and are detected by specialized cells in the cochlea. The round window acts as a release valve for the vibrations. - Note in the bottom panel the organization of the cochlea. The cochlear duct contains the organ of Corti and three compartments – the scala vestibuli, the scala media, and the scala tympani – all of which will be detailed in the following slide. - The cell bodies of cochlear neurons, or spiral ganglia, wrap around the modiolus of the cochlea. Their axons come together as the cochlear nerve found in the center of the modiolus.
  • 6. - The 3 membranous tubes of the cochlea are shown at higher magnification: - scala vestibuli – perilymph - scala media (cochlear duct) – endolymph - scala tympani – perilymph - The scala vestibuli and scala media are separated by the vestibular (Reissner’s) membrane. The scala media and scala tympani are separated by the basilar membrane, which is not a basement membrane but instead includes the organ of Corti. - The basilar membrane oscillates in response to various frequencies transmitted from the oval window. Low frequency sounds vibrate near the apex of the cochlea, while high frequency is sensed near the base. - Note the 3 outer hair cells (labeled 1, 2, 3) with apical stereocilia displaced by the tectorial membrane when the basilar membrane vibrates. The reticular lamina is a rigid plate of cytoplasm that prevents abnormal displacement of the stereocilia and subsequent depolarization. The hair cells are supported by phalangeal cells. - The inner and outer pillar cells are filled with microtubules to provide a rigid, triangular inner tunnel. This remains rigid to allow the organ of Corti to rock back and forth, instead of collapsing on itself by the vibrations. - Inner hair cells are found as a single row near the
  • 7. - Within the bony vestibule, we find the utricle and the saccule of the membranous labyrinth. It is very difficult to identify one from the other without seeing surrounding structures. The utricle is closer to the semicircular ducts, while the saccule is closer to the cochlea. The utricle and saccule are filled with endolymph, while the surrounding vestibule with loose connective tissue contains perilymph. - Both the utricle and saccule contain a neurosensory area known as the macula. This consists of hair and supporting cells overlaid by a gelatinous otolithic membrane covered with otoliths or otoconia. Displacement of the otolithic membrane moves the stereocilia of the hair cells, allowing the maculae to sense linear acceleration.
  • 8. - The three semicircular ducts are oriented in 3 perpendicular planes. This allows detection of angular acceleration. At the origin of each semicircular duct near the utricle, there are ampullae. Each one of these dilations has a crista ampullaris projecting into the lumen. - The thickened sensory epithelium at the tip of the crista contain many neurosensory cells with stereocilia, which is similar to the macula. The hair cells insert into the cupula, which is a gelatinous material similar to the otolith membrane but lacking any otoliths. The cupula shown in the bottom right appears dehydrated. - Like other parts of the inner ear, the membranous part of the semicircular duct contains endolymph while the bony part contains perilymph.
  • 9. EAR, HEARING & BALANCE In the inner ear are the organs for the senses of hearing and balance - the cochlea and the vestibular apparatus The outer and middle ear get airborne sound to the inner ear. Most of the balance information provided is not ‘sensed’, but ‘balance‘ will do to get us started The signals are turned into nerve-cell electrical activity by mechanoreception for sensing fluid movement so we shall start with this idea in lower animals that need to know what water currents are around them and how they are moving in relation to the water. Then we’ll see how sensing the movement of special fluid in the vestibular apparatus informs on how the head is positioned and is moving
  • 10. The ‘HAIRS’ of HAIR CELLS Thus far, we have spoken of hairs as they were known to microscopists for the first half of the last century. The electron microscope revealed that each ‘hair’ consists of one kinocilium at the side of an array of many non-motile sensory stereocilia. (These stereocilia are not the absorptive kind found in the male repoductive tract.) A cell - View from on top Cilium Viewed from the side, the stereocilia differ regularly in height, becoming shorter going away from the tall kinocilium They are more numerous than shown (70 per cell), and are attached by links near their tips Stereocilia
  • 11. HAIR-CELL DIRECTIONAL SENSITIVITY Kinocilium Viewed from the side, the stereocilia vary regularly in height, becoming shorter going away from the tall kinocilium Stereocilia Sensitive to bending: Tip links between stereocilia Plate for attachment of actin cores of stereocilia Vesicles & tubules Afferent axon Synapse Towards kinocilium causes cell depolarization, and increased afferent fiber firing Bending away from kinocilium causes cell hyperpolarization, and decreased afferent fiber firing
  • 12. CUPULA The bending of the hairs sometimes is coordinated and amplified by imbedding the hairs in a gelatinous body called the cupula CANAL FLUID CUPULA HAIR CELLS
  • 13. HAIR-CELL SIGNAL TRANSDUCTION Kinocilium How does bending towards kinocilium cause cell depolarization, and increased Stereocilia afferent fiber firing? Tip links between stereocilia Transduction channels for cations, e.g., Ca2 +, K+ are opened by the bending The entering cations depolarize the cell Vesicles & tubules Synapse which increase s transmitter release at the base, raising the firing rate in the axon
  • 14. Supporting, basal, mantle, etc cells Electron microscopy also revealed that the ‘supporting’ cells were of various different kinds Certain of the supporting cells secrete the gelatinous (glycoprotein) cupula Nerve fibers and synapses were both afferent, and coming from the CNS as effferent (controlling) Afferent synapses were of more than one kind, as are the hair cells Although there was a fundamental pattern, species differences were widepsread in ‘hairs, sensory cells, ‘supporting’ cells, and almost all aspects of the receptor structures
  • 15. VESTIBULAR APPARATUS I Spaces form in the skull’s temporal bone on each side for three differently oriented CANALS communicating with a larger space - VESTIBULE - to hold a system of fluid-filled bags & tubes The fluid in the bags - endolymph has a special ionic composition to allow for efficient depolarization, when the hair-cell stereocilia are deflected. Each canal, and the hair cells positioned within it, provide nervous signals responsive to movement of the head in a particular way. The three mutually perpendicular canals on each side can thus inform on any angularly accelerated (rotary) head movement
  • 16. VESTIBULAR APPARATUS II Semicircular canal & duct BONE SEMICIRCULAR CANAL containing Perilymph SEMICIRCULAR DUCT containing Endolymph Always an initial source of confusion - the semicircular space in the bone is the CANAL Inside, and attached to the wall, is the smaller membranous tube the DUCT The rest of the space in the canal is taken by a loose arachnoidlike tissue, occupied by CSF-like perilymph The duct is filled with endolymph, high in K+, & made elsewhere When the head moves in the plane of the canal, the endolymph lags a little in relation to the canal’s & duct’s movement
  • 17. VESTIBULAR APPARATUS III Duct’s Ampulla & Christa At one end of the canal, where it opens into the bony vestibule, the duct swells out, then constricts, creating the ampulla SEMICIRCULAR DUCT BONE ENDOLYMPH Endolymph CUPULA SEMICIRCULAR CANAL Perilymph AMPULLA Raised ridge CRISTA - with hair cells & gelatinous cupula Opening into utricle
  • 18. VESTIBULAR APPARATUS IV Duct & Christa Activity As th head moves so , the endolymph in this duct lags along with the cupula SEMICIRCULAR DUCT BONE ENDOLYMPH Endolymph CUPULA SEMICIRCULAR CANAL Perilymph But moving with the head are the tissues, including the hair cells So the hair cells are bent by the dragging cupula causing opening or closing of the cation channels, with change in hair-cell polarization & synaptic drive to the christa axons
  • 19. VESTIBULAR APPARATUS V Saccule & Utricle MACULA of Utricle Ampulla of superior semicircular duct start of superior semicircular duct UTRICLE Utricular Duct MACULA of Saccule SACCULE SACCULE Saccular Duct
  • 20. VESTIBULAR APPARATUS VI Saccule versus Utricle Both contain endolymph & are connected via the U & S ducts Both utricle & saccule contain a macula with hair cells Both maculae are covered with a gelatinous otolithic membrane MACULA of Utricle UTRICLE but The maculae are oriented differently Saccule’s near vertical; Utricle’s near horizontal The utricle is much larger Utricular Duct The utricle has the six openings for the 3 semicircular ducts MACULA of Saccule SACCULE Saccular Duct
  • 21. VESTIBULAR APPARATUS VII Macula Structure Endolymph OTOLITHIC MEMBRANE Connective tissue Crystalline OTOCONIA on gelatinous OTOLITHIC MEMBRANE HAIR CELLS Supporting cells Basement membrane AXONS of vestibular ganglion neurons Being in pairs, and in different orientations, the maculae can sense the head’s position and its linear movement The OTOCONIA of calcium salts and protein contribute to the effect of gravity on the hair cells, providing a vestibular drive to eventually keep ‘postural’ skeletal muscles active in maintaining one’s posture
  • 22. VESTIBULAR APPARATUS VIII Vestibular nerve & Ganglion Ampulla of superior semicircular duct CRISTA start of superior semicircular duct The vestibular ganglion & nerve lie in the bony internal acoustic meatus UTRICLE Bipolar neurons VESTIBULAR NERVE MACULA of Utricle MACULA of Saccule SACCULE VESTIBULAR GANGLION
  • 23. TEMPORAL BONY SPACES We have seen that: the semicircular ducts require three canals in each temporal bone; the utricle and ampullae, & the saccule, need a vestibule in the bone; and the vestibular ganglion & nerve need a passageway (meatus) to reach the brainstem. Also, within the bone, spaces must be found for the air vibrations to be conveyed to the cochlea; while air pressure has to be equilibrated across the ear drum The cochlea has to have its own coiled space in the bone Finally, passages (aqueducts) are needed to keep the two fluids - perilymph and endolymph - in balance The intricate result is best depicted initially as a crude diagram for learning parts and relations
  • 24. SEMICIRCULAR CANALS TEMPORAL BONE D UE AQ T UC CRANIAL CAVITY S VESTIBULE MASTOID AIR CELLS EXTERNAL CANAL COCHLEA MIDDLE EAR EUSTACHIAN TUBE It showed very well, but diagrammatically, the many bony spaces of the ear, and how the membranous compartments related to these. We’ll then return to the utricle & saccule
  • 25. SEMICIRCULAR CANALS TEMPORAL BONE One not shown AQ DU UE CRANIAL CAVITY TS C VESTIBULE MASTOID AIR CELLS EXTERNAL CANAL COCHLEA MIDDLE EAR BONY CAVITIES EUSTACHIAN TUBE
  • 26. SEMICIRCULAR CANALS UTRICLE & SACCULE TEMPORAL BONE VESTIBULE UTRICLE AQ CRANIAL CAVITY TS C DU UE SACCULE COCHLEA MIDDLE EAR EXTERNAL CANAL EUSTACHIAN TUBE
  • 27. SEMICIRCULAR CANALS PERILYMPH FLUID CONNECTIONS I ENDOLYMPH DUCT UTRICLE ENDOLYMPH SAC BRAIN CSF TS C DU UE AQ PERILYMPH DUCT SACCULE COCHLEA MIDDLE EAR PERILYMPH Perilymph & Brain’s CSF are in continuity via the Perilymphatic Duct
  • 28. SEMICIRCULAR CANALS PERILYMPH FLUID CONNECTIONS II ENDOLYMPH DUCT UTRICLE ENDOLYMPH SAC BRAIN CSF TS C DU UE AQ PERILYMPH DUCT SACCULE COCHLEA PERILYMPH Endolymph fills the utricle, saccule, semicircular ducts, and scala media of the cochlea, with several small connecting tubes for continuity Also, endolymph passes up the endolymphatic duct to a sac in the dura, from whence excess fluid can filter into the CSF
  • 29. ENDOLYMPH SYSTEM SEMICIRCULAR DUCTS ENDOLYMPH SAC BRAIN AMPULLA CSF UTRICLE TS C DU UE AQ ENDOLYMPH DUCT COCHLEA SACCULE Utricular Duct Saccular Duct Ductus reuniens COCHLEAR DUCT Scala media
  • 30. ENDOLYMPH SYSTEM II SEMICIRCULAR DUCTS & AMPULLAE UTRICLE Utricular Duct } ENDOLYMPHATIC DUCT & SAC Saccular Duct SACCULE Ductus reuniens COCHLEAR DUCT (Scala media)
  • 31. EAR, HEARING & BALANCE In the inner ear are the organs for the senses of hearing and balance - the cochlea and the vestibular apparatus The outer and middle ear get airborne sound to the inner ear. The signals are turned into nerve-cell electrical activity by mechanoreception for sensing fluid movement so we shall start with this idea in lower animals that need to know what water currents are around them and how they are moving in relation to the water. Having seen how sensing the movement of special fluid in the vestibular apparatus informs on how the head is positioned and is moving, we can examine how sounds are sensed in the cochlea
  • 32. COCHLEAR APPARATUS I Spaces form in the skull’s temporal bone on each side for three differently oriented CANALS communicating with a larger space - VESTIBULE - to hold a system of fluid-filled bags & tubes Also, coming off the vestibule is the snail-like bony cochlea with 21/2 turns The cochlear duct inside contains endolymph , with a special ionic composition to allow for efficient depolarization, when the hair-cell stereocilia are deflected. The deflection arises from membrane deflections, ultimately derived from air vibrations outside the head
  • 33. TEMPORAL BONY SPACES We have seen that: the semicircular ducts require three canals in each temporal bone; the utricle and ampullae, & the saccule, need a vestibule in the bone; and the vestibular ganglion & nerve need a passageway (meatus) to reach the brainstem. (Other nerves pass by.) Also, within the bone, spaces must be found for the air vibrations to be conveyed to the cochlea; while air pressure has to be equilibrated across the ear drum The cochlea has to have its own coiled space in the bone Finally, passages (aqueducts) are needed to keep the three fluids - perilymph, endolymph, & CSF - in balance The intricate result is best depicted initially as a diagram for learning parts and relations, but first a more anatomical overview of the whole system
  • 34. EAR OVERALL Meninges Cranial cavity FACIAL NERVE VIIIth NERVE Semicircular CANALS AURICLE VESTIBULE EAR CANAL COCHLEA EAR DRUM MIDDLE EAR Auditory/Eustachian TUBE Nasopharynx CARTILAGE
  • 35. SEMICIRCULAR CANALS TEMPORAL BONE One not shown AQ DU UE CRANIAL CAVITY TS C VESTIBULE MASTOID AIR CELLS EXTERNAL CANAL COCHLEA MIDDLE EAR BONY CAVITIES EUSTACHIAN TUBE
  • 36. COCHLEA II BRAIN SACCULE UTRICLE Two chambers connect COCHLEA Ductus reuniens Note the TWO chambers for perilymph with the Scala media in between COCHLEAR DUCT or Scala media
  • 37. COCHLEA III One turn - Compartments BONE Scala vestibuli PERILYMPH BONE Scala tympani Osseous spiral lamina PERILYMPH Reissner’s membrane COCHLEAR DUCT or Scala media ORGAN of CORTI Basilar membrane
  • 38. COCHLEA IV Bony Modiolus HELICOTREMA where Scalae vestibuli & tympani connect The cochlea spirals around a bony core - the Modiolus Note that although, in a section, we see five profiles, the structures spiral continously e.g., OSSEOUS SPIRAL LAMINA M O D I O L U S Scala vestibuli COCHLEAR DUCT or Scala media Scala tympani
  • 39. COCHLEA IV Spiral ganglion & Modiolus The modiolus is very spongy bone , filled with nerve fibers becoming the cochlear nerve SPIRAL GANGLION ORGAN of CORTI Also, the VIIIth nerve has incoming efferent fibers to influence the outer hair cells in the Organ of Corti ’efferent’ - from brain-stem neurons Axons to Inner hair cells derive from spiralganglion cell bodies
  • 40. COCHLEA VI Basilar membrane I Osseous spiral lamina BONE Scala vestibuli PERILYMPH BONE SPIRAL LIGAMENT STRIA VASCULARIS makes endolymph Scala tympani PERILYMPH The basilar membrane is tensed between the osseous spiral lamina & the spiral ligament Basilar membrane
  • 41. COCHLEA VII Basilar membrane II The spiralling hides that the basilar membrane is LONG The basilar membrane is vibrated by fluid pressures in the Scala typani Its WIDTH & STIFFNESS alter regularly along its length, so that COCHLEAR DUCT or Scala media BONE Scala vestibuli The high-frequency response is at the base The particular component frequencies of a ‘sound’ produce a pattern of vibrations along the basilar membrane, PERILYMPH BONE Scala tympani PERILYMPH Vibrations from oval window of vestibule It vibrates well to low frequency sounds at its apex ORGAN of CORTI detectable by the inner hair cells attached to the active regions of the Basilar membrane
  • 42. Tectorial membrane & Inner Hair Cell TECTORIAL MEMBRANE is gelatinous, like the cupula, but is attached at one side, aside from its hair-cell connections Support for Reissner’s membrane & Tectorial membrane TECTORIAL MEMBRANE with attached ENDOLYMPH SPIRAL LIMBUS Scala tympani INNER HAIR CELL innervated by axon from spiralganglion neuron Basilar membrane
  • 43. Organ of Corti - cell types Crista & Macula -- “Electron microscopy also revealed that the ‘supporting’ cells were of various different kinds”. Far more true for the Organ of Corti, and detectable already in the 19th century, hence some eponyms TECTORIAL MEMBRANE TECTORIAL CELLS INNER HAIR CELL OUTER HAIR CELLS SPIRAL LIMBUS HENSEN & CLAUDIUS CELLS Basilar membrane INNER & OUTER PHALANGEAL CELLS DEITER’S INNER & OUTER PILLAR CELLS
  • 44. Stria vascularis & K+ recycling I The Kcc4 channel gets the K+ into the Deiter’s cells, whence it goes via gap junctions to theStria for pumping into the endolymph STRIA CELLS FIBROBLASTS OUTER HAIR CELLS INNER HAIR CELL K+ HENSEN & CLAUDIUS CELLS Basilar membrane INNER & OUTER OUTER PHALANGEAL CELLS PILLAR CELLS DEITER’S
  • 45. Stria vascularis II The Stria vascularis was so named because, quite unusually, capillaries are found amongst the three kind of epithelial cells STRIA CELLS HENSEN & CLAUDIUS CELLS Basilar membrane
  • 46. SOUND CONDUCTION TO THE INNER EAR We’ll return to the schematic of the whole auditory system for: The cochlea has to have its own coiled space in the bone Also, within the bone, spaces must be found for the air vibrations to be conveyed to the cochlea; while air pressure has to be equilibrated across the ear drum The membrane-sealed openings - oval & round windows - from vestibule to middle ear, allowing transmission of pressures, but keeping in the perilymph The tympanic membrane (ear drum) separating outer auditory meatus from the middle ear
  • 47. LIMITS SEMICIRCULAR CANALS AQ DU UE TS C CRANIAL CAVITY VESTIBULE MASTOID AIR CELLS EXTERNAL CANAL - OPEN EAR COCHLEA MIDDLE EAR OVAL DRUM WINDOW TEMPORAL BONE ROUND WINDOW EUSTACHIAN TUBE - OPEN
  • 48. LININGS PERIOSTEUM CRANIAL CAVITY SEMICIRCULAR CANALS PERIOSTEUM AQ DU UE TS C VESTIBULE MASTOID AIR CELLS EXTERNAL CANAL COCHLEA MIDDLE EAR ‘SKIN’ MENINGES TEMPORAL BONE ‘AIRWAY’ MUCOSA EUSTACHIAN TUBE
  • 49. LININGS of BONY SPACES ‘SKIN’ EXTERNAL AUDITORY CANAL MIDDLE EAR EUSTACHIAN TUBE VESTIBULE COCHLEA MASTOID AIR CELLS SEMICIRCULAR CANALS PERIOSTEUM CRANIAL CAVITY MENINGES ‘AIRWAY’ MUCOSA OTIC DUCT
  • 50. AUDITORY OSSICLES SEMICIRCULAR CANALS MALLEUS INCUS AQ OVAL WINDOW S CT DU UE STAPES VESTIBULE COCHLEA MASTOID AIR CELLS STAPES INCUS MALLEUS EXTERNAL CANAL EAR DRUM ROUND WINDOW MIDDLE EAR EUSTACHIAN TUBE
  • 51. AUDITORY OSSICLES II OVAL WINDOW VESTIBULE ROUND WINDOW To relieve fluid pressures in the vestibule STAPES INCUS MALLEUS EXTERNAL CANAL EAR MALLEUS INCUS STAPES MIDDLE EAR DRUM The malleus (hammer) is vibrated by air impinging on the tympanic membrane (ear-drum). Malleus movements drive the incus (anvil), which in its turn moves the stapes (stirrup) in and out of the oval window, so pulsating the fluid (perilymph) in the vestibule. The bony chain & geometry amplify the air’s initial force.
  • 52. AUDITORY OSSICLES II OVAL WINDOW VESTIBULE ROUND WINDOW To relieve fluid pressures in the vestibule STAPES INCUS MALLEUS EXTERNAL CANAL EAR MALLEUS INCUS STAPES MIDDLE EAR DRUM The malleus (hammer) is vibrated by air impinging on the tympanic membrane (ear-drum). Malleus movements drive the incus (anvil), which in its turn moves the stapes (stirrup) in and out of the oval window, so pulsating the fluid (perilymph) in the vestibule. The bony chain & geometry amplify the air’s initial force (& match impedance)
  • 53. AUDITORY OSSICLES III The malleus (hammer) is vibrated by air impinging on the tympanic membrane (ear-drum). Malleus movements drive the incus (anvil), which in its turn moves the stapes (stirrup) in and out of the oval window, so pulsating the fluid (perilymph) in the vestibule. The bony chain & geometry amplify the air’s initial force. EAR DRUM MALLEUS INCUS STAPES OVAL WINDOW
  • 54. Stapedius muscle & Facial nerve Tympanic cavity/ Middle ear FACIAL NERVE INCUS the Stapedius muscle whose contraction hinders the movement of the STAPES so protecting the ear from loud sounds along with Tensor tympani‘s action ( Stapedius muscle Oval window Other long spaces in the bone house the Facial nerve & VESTIBULE The two responses constitute Sound attenuation reflex
  • 55. TENSOR TYMPANI Tensor tympani muscle has its bony tunnel parallel to Eustachian tube’s VESTIBULE AURICLE MIDDLE EAR EAR CANAL V th NERVE COCHLEA Auditory TUBE Malleus Tensor tympani muscle TT tendon TT contraction limits Malleus movement for protection from loud sounds
  • 56. EMBRYOLOGY I COCHLEA II LININGS BRAIN CRANIAL CAVITY SEMICIRCULAR CANALS PERIOSTEUM SACCULE TS UC ED QU A UTRICLE VESTIBULE Two chambers connect COCHLEA MASTOID AIR CELLS EXTERNAL CANAL COCHLEA MIDDLE EAR TEMPORAL BONE EUSTACHIAN TUBE Ductus reuniens Note the TWO chambers for perilymph with the Scala media in between PERIOSTEUM ‘AIRWAY’ MENINGES ‘SKIN’ MUCOSA COCHLEAR DUCT or Scala media MEMBRANOUS LABYRINTH The linings are clues to the several structures involved in ear formation The precursors of the linings sent signals to surrounding mesenchyme, to construct structures to house what they themselves were engaged in forming
  • 57. Full-face view 4-w embryo What is going on inside the cranial end of the embryo? E.g., plans for Inner & Middle ear? BRAIN I II I CORD HEART II CARDIAC BULGE Mid-sagittal section
  • 58. Mid-sagittal section of 1-m embryo PHARYNGEAL ARCHES covered by ectoderm PHARYNGEAL POUCHES lined by endoderm BRAIN I II Pouch pattern is more complicated & does not quite match arch pattern Next slides will schematize & simplify floor of Arches I-IV
  • 59. Pharyngeal groove I PHARYNGEAL POUCHES: inside for ear canal Endodermal lining of pharyngeal pouch for Middle ear ARCH I II Endodermal lining of pharyngeal pouch III IV Ectodermal covering Mesenchymal core makes, for instance, the ossicles Arch cut into
  • 60. SOURCES OF EAR LININGS The linings are clues to the several structures involved in ear formation PHARYNGEAL POUCHES lined by endoderm ‘AIRWAY’ MUCOSA of Middle ear PHARYNGEAL ARCHES covered by ectoderm I II BRAIN ‘SKIN’ of ear canal Neural crest MESECTODERM Ectodermal OTIC PLACODE but lying laterally MEMBRANOUS LABYRINTH MENINGES PERIOSTEUM but later, when bone has formed
  • 61. OTIC PLACODE Lens & Olfactory similar OTIC PLACODE BRAIN ECTODERM Neural crest MESECTODERM OTIC PLACODE’s rim rises, so creating, then deepening the otic pit in preparation for forming a vesicle OTIC VESICLE is already defining upper & lower parts of membranous labyrinth U L
  • 62. OTOCYST SITE & DEVELOPMENT 7 weeks Semicircular Duct 5 weeks Endolymphatic duct Utr BRAIN Utricle Rhombencephalon Sa U L OTIC VESICLE/CYST Mesenchyme for OSSICLES Ist PHARYNGEAL CLEFT TUBULO-TYMPANIC RECESS Cochlear Duct Sacc Semicircular Duct
  • 63. Semicircular Duct Semicircular Canal Development Endolymphatic duct Utricle Sa Utr 7 weeks Cochlear Duct Outpouching in one plane Sacc Duct left open Membranes dissolve Constriction Membranes come together Utricle Duct Utricle
  • 64. SOURCES OF EAR LININGS The linings are clues to the several structures involved in ear formation Ectodermal OTIC PLACODE MEMBRANOUS LABYRINTH PHARYNGEAL ARCHES covered by ectoderm PHARYNGEAL POUCHES lined by endoderm ‘SKIN’ of ear canal ‘AIRWAY’ MUCOSA OTIC VESICLE/ OTOCYST Ist PHARYNGEAL CLEFT TUBULO-TYMPANIC RECESS of Middle ear Neural crest MESECTODERM MENINGES Neural crest MESECTODERM PERIOSTEUM around cranial NEURAL TUBE BONES
  • 65. 4-w/3.5mm EMBRYO Full-face Remains of FRONTONASAL PROMINENCE after development of nasal placodes NASAL PLACODE OPTIC PLACODE MAXILLARY PROCESS STOMODEUM with perforating membrane MANDIBULAR ARCH HYOID ARCH CARDIAC BULGE FACE
  • 66. Arch Relations CRANIAL NERVE ARCH Trigeminal V I Facial VII Stapedius muscle II MALLEUS INCUS Tensor tympani muscle Glossopharyngeal IX III Vagus X IV STAPES
  • 67. EAR PATHOLOGY Wax, foreign Overgrowth of bone - Otosclerosis bodies in canal Excess endolymph - hydrops Ankylosed ossicles Meningitis, FACIAL abscess NERVE VIIIth Angle tumor NERVE -Neuroma of AURICLE VIIIth N - bad balance /hearing Lost Hair cells - loud noises, age, streptomycin, neomycin, cisplatin Blocked tube V EAR CANAL COCHLEA EAR DRUM MIDDLE EAR CARTILAGE Perforated ear-drum -infection, blast injury Eustachian TUBE Otitis media - middle ear infection; Cholesteatoma - kerat strat squam ep Nasopharynx Auditory/
  • 68. EAR PATHOLOGY II Lost/damaged Hair cells from - loud noises, age; ototoxic agents - streptomycin, neomycin (aminoglycoside antibiotics), cisplatin (anticancer agent) Congenital deafness - One of a number of defects in genes can impair the development of the inner ear, or the differentiation and functioning of hair cells Hypothyroidism and iodine deficiency in pregnancy can result in defective development of the fetus’ Organ of Corti
  • 69. EAR PATHOLOGY III Overgrowth of bone Otosclerosis Angle tumor -Neuroma of VIIIth N - bad Ankylosed ossicles Meningitis, abscess balance /hearing Lost Hair cells - loud noises, age, streptomycin, Excess endolymph hydrops Congenital deafness - defects in genes Blocked Eustachian tube Wax, foreign bodies in canal Otitis media - middle ear infection Perforated ear-drum -infection, blast