Hearing and Deafness

Sarah Todd

BIO 313

22 February 2006

http://www.drawingpower.org.uk/Themes04/Themes2004.htm

Sense of Hearing

• Sound physics– Sound energy transmitted through

gaseous/liquid/solid medium

– Vibration of medium’s molecules

– Sound wave• ↑ amplitude: ↑ loudness

• ↑ vibration: ↑ pitch

• 1000-4000 Hz

• Physiology of:– External, middle, inner ear

– Nerves of the brain

– Processing of acoustic information by brain parts

http://www.engr.uconn.edu/~escabi/DynamicAuditoryStimuli.html

http://www.bananasontoast.org/?cat=12

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)

http://www.open2.net/labrats/gforce_science.htm

Anatomy of the EarSemicircular canal

Temporal bone

http://www.acoustics.org/press/140th/noca.htm

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

http://anatomy.iupui.edu/courses/histo_D502/D502f04/lecture.f04/Earf04/Ear.f04.html

http://ourworld.compuserve.com/homepages/dp5/evod3.htm

Organ of Corti

http://www.iurc.montp.inserm.fr/cric/audition/english/corti/hcells/transd/transd.htm

http://www.rockefeller.edu/labheads/hudspeth/graphicalSimulations.php

Neural Pathways in HearingCochlear 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

http://news.bbc.co.uk/1/hi/scotland/1803505.stm

Bibliography Widmaier, E.P., Raff, H., Strang, K.T. Vander’s Human

Physiology: The Mechanisms of Body Function. 10th ed. Boston: McGraw-Hill, 2005.

Lynch, E.D., Lee, M.K., Morrow, J.E., Welcsh, P.L., Leon, P.E., King, M.-C. 1997 Nonsyndromic Deafness DFNA1 Associated with Mutation of a Human Homolog of the Drosophila Gene diaphenous. Science. 278:1315-1318.

Laurent Clerc National Deaf Education Center, Gallaudet University. “Information of Deafness.” 2006. <http://clerccenter.gallaudet.edu/about/faq.html#deaf3 >.

Images/Animations from Google.com