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Understanding the Auditory System: External Ear Anatomy and Functions

Explore the peripheral auditory system, specifically the external ear components, functions, and resonance effects. Learn about the anatomy, directional terms, and essential pathways of sound localization. Discover the importance of inter-aural differences in auditory perception.

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Understanding the Auditory System: External Ear Anatomy and Functions

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  1. Parts of the auditory system • Peripheral • External ear • Middle ear • Inner ear • Auditory nerve • Central • Cochlear nucleus • Superior olivary complex • Lateral leminiscus • Inferior colliculus • Medial geniculate body • Auditory subcortex • Cortex • Interhemispheric pathways

  2. Anatomical terms • Planes of section: • Frontal/Coronal: Front and back • Sagittal: Left and right • Median/Midsagittal: Through the center • Axial/Horizontal/Transverse: Upper and lower http://www.spineuniverse.com/displayarticle.php/article1023.html

  3. Anatomical directions • Anterior/Ventral: Front • Posterior/Dorsal: Back • Inferior: Bottom • Superior: Top • Lateral: Away from median plane • Medial: Toward the median plane

  4. Anatomy of the auditory system • Contained in the temporal bone • Located on the sides of the skull

  5. Parts of the temporal bone • Squamous • Mastoid • Tympanic • Petrous Medial view of right ear. Note: IAM is internal auditory meatus, which is different from the external auditory meatus. Lateral view of right ear

  6. Anatomy of the ear • http://www.iurc.montp.inserm.fr/cric51/audition/english/ear/fear.htm • http://www.wiley.com/legacy/college/bio/tortora366927/resources/student/anatomydrill/ch16.html

  7. Parts of the auditory system • Peripheral • External ear • Middle ear • Inner ear • Auditory nerve • Central • Cochlear nucleus • Superior olivary complex • Lateral leminiscus • Inferior colliculus • Medial geniculate body • Auditory subcortex • Cortex • Interhemispheric pathways

  8. External ear • Consists of • Auricle or Pinna: Mostly cartilage • External auditory canal/meatus http://www.ghorayeb.com/AnatomyAuricle.html

  9. Parts of the Pinna • Concha: Bowl or deep central portion • Helix: Prominent ridge that begins superior to the opening of the canal and runs around the pinna • Antihelix: Interior ridge parallel to the helix • Triangular fossa: Triangular depression formed anteriorly and superiorly by the helix • Lobule: Most inferior part of the pinna • Tragus: Small flap at the anterior side of the concha

  10. External auditory meatus • Length is approximately 28 mm • Diameter is approximately 7 mm • Not perfectly straight • Ends in the tympanic membrane • Outer half of the canal formed by cartilage • Skin secretes cerumen • Medial part formed by bone from the squamous and tympanic portions of the temporal bone

  11. External ear functions • Modifies the spectrum of incoming sounds. • Resonance of external auditory meatus • Head related transfer functions • Protection to middle and inner ear structures

  12. Resonance of ear canal • Resonance of ear canal: Around 2.5 kHz • Resonance of the concha: Around 5 kHz Net effect: Boost in frequency region between 1.7 and 7 kHz

  13. External ear functions • Modifies the spectrum of incoming sounds. • Resonance of external auditory meatus • Head related transfer functions • Protection to middle and inner ear structures

  14. Head-related transfer functions • Inter-aural amplitude/level difference • Inter-aural time difference Important for sound localization

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