Download Physiology of Hearing Talk

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
http://www.bananasontoast.org/?cat=12
• Physiology of:
– External, middle, inner ear
– Nerves of the brain
– Processing of acoustic information by
brain parts
http://www.engr.uconn.edu/~esc
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
http://www.open2.net/labrats/gforce_science.htm
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
Organ of Corti
http://ourworld.compuserve.com/homepages/dp5/evod3.htm
Neural Pathways in Hearing
Cochlear nerve fibers
↓
interneurons (brainstem)
↓
multineuron pathway
↓
thalamus
↓
auditory cortex (temporal lobe)
http://www.iurc.montp.inserm.fr/cric/audition/english/corti/hcells/transd/transd.htm
http://www.rockefeller.edu/labheads/hudspeth/graphicalSimulations.php
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