Physiology Hearing System Behrouz Mahmoudi www soran edu

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

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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 4 th 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