Hearing and Deafness Sarah Todd BIO February

Sense of Hearing Sound physics –Sound energy transmitted through gaseous/liquid/solid medium –Vibration of medium’s molecules –Sound wave ↑ amplitude: ↑ loudness ↑ vibration: ↑ pitch Hz Physiology of: –External, middle, inner ear –Nerves of the brain –Processing of acoustic information by brain parts abi/DynamicAuditoryStimuli.html

Sound Transmission in the Ear External Ear: –External auditory canal→ tympanic membrane Middle Ear: –Tympanic membrane → middle ear: malleus → incus → stapes → oval window membrane Inner Ear: –Middle ear → inner ear: scala vestibuli → cochlear duct → organ of Corti → stereocilia → action potential along cochlear nerve Nerves of the Brain: –Cochlear nerve → brainstem (interneurons) → thalamus → auditory cortex (temporal lobe)

Anatomy of the Ear Semicircular canal Temporal bone

Hair Cells of the Organ of Corti Inner ear/cochlea: sensory receptor cells Hair cells = mechanoreceptors Stereocilia attached to/stimulated by basilar membrane: –Cell depolarization –Cell repolarization ↑ loudness (energy): ↑ action potential frequency

Organ of Corti

Neural Pathways in Hearing Cochlear nerve fibers ↓ interneurons (brainstem) ↓ multineuron pathway ↓ thalamus ↓ auditory cortex (temporal lobe)

Loss of Hearing Exposure to high-intensity noises + Exposure to chronic noise levels ↓ Hair cells easily damaged/destroyed 20 million Americans –1/12 Americans – 8.6% population Causes: –Heredity (50%) –Accidents/Illness (50%) Hearing aids Cochlear implants

Bibliography  Widmaier, E.P., Raff, H., Strang, K.T. Vander’s Human Physiology: The Mechanisms of Body Function. 10 th ed. Boston: McGraw-Hill,  Lynch, E.D., Lee, M.K., Morrow, J.E., Welcsh, P.L., Leon, P.E., King, M.-C Nonsyndromic Deafness DFNA1 Associated with Mutation of a Human Homolog of the Drosophila Gene diaphenous. Science. 278:  Laurent Clerc National Deaf Education Center, Gallaudet University. “Information of Deafness.”  Images/Animations from Google.com