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EAR

EAR. EAR. External (outer) ear - channels sound waves to middle ear Middle ear - directs sound waves to oval window Internal (inner) ear - contains mechanoreceptors (hair cells) for hearing & equilibrium. Outer Ear.

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EAR

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  1. EAR

  2. EAR • External (outer) ear - channels sound waves to middle ear • Middle ear - directs sound waves to oval window • Internal (inner) ear - contains mechanoreceptors (hair cells) for hearing & equilibrium

  3. Outer Ear • Fleshy auricle (pinna) directing air vibrations down auditory canal (external auditory meatus)

  4. MIDDLE EAR • Air-filled cavity in temporal bone • Separated from the exterior by the tympanic membrane (ear drum) • Filled with air by auditory tube (Eustachian tube) connected to nasopharynx • The auditory tube opens during swallowing or yawning to equalize air pressure on both sides of eardrum. • Ear ossicles span tympanic cavity - held in place by tensor tympani and stapedius muscles

  5. Anatomy of Middle Ear

  6. INNER EAR • Consists of: 1. Bony labyrinth - passageways in the temporal bone that contain perilymph 2. Membranous labyrinth - fleshy tubes lining bony tunnels filled with endolymph and floating in perilymph • Houses cochlea and vestibular apparatus

  7. Anatomy of the Cochlea 2.5 coils 3 fluid-filled chambers Organ of Corti

  8. HOW THE EAR WORKS • Eardrum vibrates & creates enough force/unit area at oval window to vibrate the endolymph in the scala vestibuli. Vibrations excite hair cells. • Contraction of tensor tympani & stapedius protect the cochlea in response to loud noises (tympanic reflex) • Contraction of tensor tympani pulls eardrum inward and tightens it. • Contraction of the stapedius reduces mobility of stapes. • The ear muscles also contract during speaking so we can hear others.

  9. SENSORY CODING • Loudness produces vigorous vibrations that excite many hair cells. This triggers higher frequency of action potentials that the brain interprets as loudness. • Determination of pitch depends on which part of the basilar membrane vibrates in the organ of Corti.

  10. Frequency Response of Basilar Membrane Peak amplitude of wave varies with frequency

  11. EQUILIBRIUM • The vestibular apparatus is concerned with equilibrium. • Maculae in saccule & utricle perceive head orientation & maintain static equilibrium • Maculae & cristae maintain dynamic equilibrium. • Maculaeperceivelinear acceleration • Cristae of semicircular ducts perceive angular acceleration

  12. SACCULE & UTRICLE • Contain maculae • A macula is a patch of hair cells with stereocilia & one kinocilium buried in a gelatinous otolithic membrane weighted with granules called otoliths.

  13. Crista Ampullaris of Semicircular Ducts • A crista ampullaris consists of hair cells buried in a mound of gelatinous membrane. • The orientation of one duct causes other ducts to be stimulated.

  14. Crista Ampullaris & Head Rotation • As the head turns, endolymph lags behind pushing cupulae and stimulating hair cells

  15. THE VESTIBULAR NERVE • Hair cells of macula sacculi, macula utriculi & semicircular ducts synapse on the vestibular nerve. • Fibers end in the vestibular nucleus of pons, cerebellum, nuclei of cranial nerves controlling eye, head and neck movements.

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