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Hearing and Equilibrium

Hearing and Equilibrium. Parts of the Ear. external ear middle ear inner ear. Parts of the Ear. inner ear. external ear. middle ear. Eustachian tube. Relationship of Ear to Mouth. External Ear. collects sound waves and passes them inward into the external auditory canal Includes:

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Hearing and Equilibrium

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  1. Hearing and Equilibrium

  2. Parts of the Ear • external ear • middle ear • inner ear

  3. Parts of the Ear inner ear external ear middle ear Eustachian tube

  4. Relationship of Ear to Mouth

  5. External Ear • collects sound waves and passes them inward into the external auditory canal • Includes: - auricle - external auditory canal - tympanic membrane

  6. Auricle • flap of elastic cartilage, flared like a funnel • covered with thick skin • helix - top • lobule - bottom, earlobe • attached to head by ligaments and muscles

  7. External Auditory Canal • curved tube about 1 inch long • skin-lined • near exterior opening are ceruminous glands - produce cerumen (wax) which helps to trap foreign material • lies in temporal bone • extends from auricle to tympanic membrane

  8. Tympanic Membrane • thin, semitransparent membrane of fibrous connective tissue • lies between external auditory canal and middle ear • cone-shaped structure with apex directed medially • sound waves in auditory canal cause pressure changes that produce eardrum vibrations

  9. Middle Ear • air-filled cavity in temporal bone • epithelium-lined • contains auditory ossicles • extends from eardrum to thin, bony partition with two membrane covered openings called oval and round window • connected to mouth by Eustachian tube

  10. Auditory Ossicles • transfer vibrations from eardrum to oval window of internal ear • maleus is attached to the internal surface of eardrum at apex • incus is the intermediate bone • stapes is attached by ligaments to the membranous oval window

  11. Auditory Ossicles (cont.) • malleous vibrates with tympanic membrane; passes vibration to incus • incus causes stapes to vibrate on oval window • oval window is pushed in and out, causing motion in fluid within internal ear • action activates receptor cells • impulses travel to temporal lobe of cerebrum and sound sensation results

  12. Inner Ear • complex series of interconnecting chambers • Includes: - bony or osseous labyrinth - membranous labyrinth

  13. Osseous Labyrinth • bony canal within the temporal bone • lined with periosteum • contains the fluid perilymph - chemically similar to cerebrospinal fluid • Divided into three areas: - semicircular canals - vestibule - cochlea

  14. Membranous Labyrinth • surrounded by cerebrospinal fluid • series of sacs following general shape of osseous labyrinth • lined with epithelium • contains endolymph - chemically similar to intracellular fluid • portions within bony canals called semicircular ducts communicate with utricle and vestibule

  15. Semicircular Canals • three canals; anterior, posterior, and lateral • each end enlarges into swelling called ampula • lie at right angles to each other • contain receptors for equilibrium

  16. Vestibule • oval central portion of bony labyrinth • contains two sacs called the utricle and saccule - connect to each other by small duct • contains receptors for equilibrium

  17. Cochlea (koklea = snail shell) • coil-shaped cavity • anterior to vestibule • makes almost three turns • central bony core called modiolus • contains thin, bony shelf which divides cochlea into upper and lower compartments and smaller cochlear duct • contains receptors for hearing

  18. Three Compartments of Cochlea • scala vestibuli • scala tympani • cochlear duct (scala media)

  19. Scala Vestibuli • above bony partition • ends at oval window • filled with perilymph Scala Tympani • below bony partition • ends at round window • contains perilymph

  20. Cochlear Duct (scala media) • portion of membranous labyrinth • separated from scala vestibuli by vestibular membrane • separated from scala tympani by basilar membrane • organ of Corti (spiral organ) located on basilar membrane within cochlear duct • tectoral membrane projects over and in contact with hair cells of spiral organ

  21. Organ of Corti • spiral organ • lined with epithelial cells - support cells and 16,000 hair cells contain receptors for auditory sensations

  22. Hair Cells • Two types: - inner - outer • processes at apical end extend into endolymph of cochlear duct • synapse with fibers of the cochlear branch of the vestibulocochlear nerve (VIII) • easily damaged by high intensity sounds

  23. Sound Waves • sound sensations are heard by vibrations transmitted through the air • result from alternate compression and decompression of air molecules • most audible sound vibrations to human ears are frequencies between 1000 and 4000 Hertz • entire audible range is 20 - 20,000 Hz

  24. Pitch • determined by frequency of vibrations • the higher the frequency of vibrations, the higher the pitch (musical high note) Loudness • determined by amplitude of sound waves • measured in decibels (dB)

  25. silence rustling leaves normal conversation crowd noise vacuum cleaner pneumatic drill uncomfortable sound painful sound 0 dB 15 dB 45 dB 60 dB 75 dB 90 dB 120 dB 140 dB Decibels of Sounds

  26. Physiology of Hearing • auricle directs waves into external auditory canal • sound waves strike tympanic membrane • alternate compression and decompression of air cause membrane vibration • movement of membrane depends on intensity and frequency of sound waves • low-frequency = slow membrane vibration • high-frequency = rapid membrane vibration

  27. Physiology of Hearing (cont.) • malleus connects in central area of tympanic membrane • malleus vibrates, conducting vibration to incus and then stapes • stapes pushes membrane on oval window in and out • movement of oval window causes waves in perilymph of cochlea

  28. Physiology of Hearing (cont.) • inward movement of oval window pushes on perilymph of scala vestibuli to scala tympani to round window into middle ear • movement of perilymph exerts pressure on vestibular membrane • pressure in endolymph inside cochlea increases and decreases

  29. Physiology of Hearing (cont.) • pressure fluctuations move basilar membrane causing hair cells of spiral organ to move against tectorial membrane leading to generation of nerve impulses in cochlear nerve fibers • pathway extends into medulla oblongata through midbrain to thalamus and on to temporal lobes of cerebrum for interpretation

  30. Physiology of Equlibrium • when body movement occurs, organs detect motion and aid in maintaining balance • organs provide information on which way is up or down • Organs of equlibrium: - utricle - saccule - semicircular ducts

  31. Two kinds of Equilibrium • static - maintenance of posture in response to changes in body orientation relative to the ground • dynamic - maintenance of body position, mainly the head, in response to sudden movements

  32. Deafness • conduction deafness - impairment of structures that transmit vibrations - punctured eardrum, otitis media, wax buildup • nerve deafness - degeneration of receptors - damage to receptor cells

  33. Ménière’s Syndrome • labyrinth disorder • characterized by fluctuating loss of hearing, vertigo, and tinnitus • caused by an increased volume of endolymph causing enlargement of the labyrinth • disease of cranial nerve VIII

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