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Physiology Hearing System Behrouz Mahmoudi www.soran.edu.iq 1 The Outer Ear Consists of: • The Pinna cartilaginous, highly variable in appearance, some landmarks. www.soran.edu.iq • External Auditory Canal (or external auditory meatus) - 2.5 cm tube. 2 Pinna Landmarks • • • • • • Helix Antihelix Concha Tragus Intertragal Notch Antitragus www.soran.edu.iq 3 External Auditory Canal • lateral portion-cartilage • medial portion-osseous • lined with epidermal (skin) tissue • hairs in lateral part • cerumen (ear wax) secreted in lateral part. www.soran.edu.iq 4 Outer Ear Functions • Amplification / Filtering • Protection • Localization www.soran.edu.iq 5 The Middle Ear: A cleft within the temporal bone • • • • Lining is mucous membrane Tympanic Membrane separates it from EAC Eustachian tube connects it to nasopharynx www.soran.edu.iq Also Connected to Mastoid Air Cells 6 Middle Ear Structures 1- Malleus 2- Incus --Ossicles 3- Stapes 4- Tympanic Membrane (Eardrum) 5- Round Window 6- Eustachian Tube www.soran.edu.iq 7 Middle Ear Muscles 1. The Stapedius Attaches to Stapes,Contracts in Response to Loud sounds, chewing, speaking; Facial (VIIth cranial) nerve 2. The Tensor Tympani Helps open Eustachian tube www.soran.edu.iq 8 Middle Ear Functions • Impedance Matching • Filtering • Acoustic Reflex www.soran.edu.iq 9 These sounds get through the middle ear most readily www.soran.edu.iq 10 www.soran.edu.iq 11 INNER EAR Two Halves: • Vestibular--transduces motion and pull of gravity • Cochlear--transduces sound energy (Both use Hair Cells) www.soran.edu.iq 12 The Stereocilia on IHCs and OHCs • OHCs (at top) • V or W shaped ranks • IHC (at bottom) • straight line ranks www.soran.edu.iq 13 Cochlear Functions • Transduction- Converting acousticalmechanical energy into electro-chemical energy. • Frequency Analysis-Breaking sound up into its component frequencies – Bekesy’s Traveling Wave – Active Tuning from OHCs www.soran.edu.iq 14 Afferent & Efferent Neurons www.soran.edu.iq 15 IHC activation alters firing rate www.soran.edu.iq 16 Major Components of the Central Auditory Nervous System (CANS) • • • • • • • VIIIth cranial nerve Cochlear Nucleus <Trapezoid Body> Superior Olivary Complex Lateral Lemniscus Inferior Colliculus Medial Geniculate Body Primary Auditory Cortex www.soran.edu.iq Brainstem Mid-brain Thalamus Temporal Lobe 17 Mid-Saggital View of Brain 4th Ventricle Corpus Callosum Cerebellum Thalamus www.soran.edu.iq Pons 18 Cortical Processing • Pattern Recognition • Duration Discrimination • Localization of Sounds • Selective Attention www.soran.edu.iq 19 Cerebral Dominance/Laterality • Language Processing in the left hemisphere. (Remember the right ear has the strongest connections to the left hemisphere) • Most people show a right-ear advantage in processing linguistic stimuli www.soran.edu.iq 20