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The Inner Ear SPA 4302 Summer 2006 INNER EAR Sensory Endorgans encased within very dense bone Two Halves: • ____________--transduces motion and pull of gravity • ____________-transduces sound energy (Both use Hair Cells) Subdivision into spaces containing ___________ (blue), and spaces containing __________ (red) Cochlea is Divided into 3 “Scala” • Scala Vestibuli – __________ Membrane • Scala Media – __________ Membrane • Scala Tympani • ___________ - the opening between 2 outer Scala Fluids filling the Inner Ear • ___________- in S. Vestibuli and S. Tympani – High Sodium / Low Potassium concentrations – Low Voltage (0 to +5 mV) • ___________- in S. Media – High Potassium / Low Sodium concentrations – High Positive Voltage (85 mV) Cross-Section of the Cochlea Third Turn Second Turn A Cross Section Shows the 3 Scala Within S. Media is the Organ of Corti I = Inner Hair Cells O = Outer Hair Cells P = Pillar Cells D = Deiter’s Cells The Stereocilia on IHCs and OHCs • ________ (at top) • V or W shaped ranks • ________ (at bottom) • straight line ranks Stereocilia bent toward tallest row • ________ flows into cell • ________ flows into cell • Voltage shifts to a less __________ value • More neurotransmitter is released Cochlear Afferent (Sensory) Neurons • __________ (95%) – synapse w/ IHC – 1 IHC to 20 neurons – well myelinated • __________ (5%) – Synapse with OHCs – Many OHCs to 1 neuron – unmyelinated Cochlear Functions • __________- Converting acousticalmechanical energy into electro-chemical energy. • ___________- Breaking sound up into its component frequencies Development of the Inner Ear • Beginning in week 3, ________________ develops, • Invaginates to form _______________, • Which then closes off, leaving an _________________. • Capsule divides into saccular, utricular divisions – ________: cochlea (begins forming in week 6) – ________: semicirc. canals, endolymphatic sac & duct • Organ of Corti forms from week ___ • Inner ear fully formed by ___ weeks Hearing Loss and Disorders of the Inner Ear • Vast majority of SNHL results from inner ear disorder. • Cochlear pts often hear, but cannot distinguish what they hear very clearly: ____________. – Arises from frequency and other distortions associated with changes in inner ear function. Inner Ear Disorders: Prenatal Causes • • • • • • Genetic mutation/inheritance Cytomegalovirus (CMV) __________ Rubella Rh incompatibility __________ Anatomical Anomalies Often seen as Bony malformations Examples: Mondini (incomplete cochlea) Enlarged Duct (shown here) Age Effects Noise Damage • Temporary Threshold Shift (TTS) • Permanent Threshold Shift (PTS) • Duration, Timing and Intensity influence • Typical “Noise Notch” often seen between ____________ first. • Notch widens and deepens over time, with hearing loss spreading to adjacent frequencies, and increasing in degree. Ototoxicity Substances poisonous to the ear • Medicines – ___________ antibiotics – ___________ drugs for CA – ___________ • Industrial Chemicals (tolulene, etc) May affect __________ Degree of hearing loss varies Synergy with noise or other ototoxic agents Meniere’s Disease • Really a Syndrome: – – – – _________ Vertigo Roaring, Low Freq. Tinnitus Fluctuating ___________ Hearing Loss Sensation of Aural Fullness • Thought to be produced by ____________________, a condition in which too much endolymph accumulates in the inner ear.
