Marine Mammal Bioacoustics: The Mammalian Ear

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Marine Mammal Bioacoustics The Mammalian Ear

• Peter M. Scheifele MDr, PhD, LCDR USN (Ret.)
• University of Cincinnati
• Communication Sciences and Disorders,
  Neuroaudiology Dept.
• University Medical Center
• scheifpr_at_uc.edu

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Auditory Pathway from the Outer to Inner Ear
(Anatomy Function)
Via CN-VIII

• Outer Ear
• (A) Pinnae
• (A) External Auditory Meatus
• (F) Collect and Direct
• (F) Vibrational Wave
• (F) Compression Refraction

Middle Ear (A) Ossicles (A) Tympanic Membrane (A)
Tympanum (A) Eustachian Tubes (F)
Mechanical Motion (F) Transfer Function Air to
Mechanical Impedance amplification
Inner Ear (A) Cochlea (A) Scala-media Organ of
Corti Basilar Membrane Hair Cells Endolymphatic
Fluid (F) Processes, samples frequency
intensity (F) Fluid wave motion

• Brain (CANS)
• CANS Medulla, Pons, Brain stem, A1 A2
• (A) Cranial Nerve VIII
• (A) Inner via spiral ganglia
• Brain via medulla cochlear nuclei
• (F) Discrimination
• (F) Localization
• (F) Processing/Perception
• (F) Integration
• (G) Electrical signal

ELECTRICAL SIGNAL
MECHANICAL WAVE
AIR WAVE
FLUID WAVE
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OUTER EAR ANATOMY

• Pinna or auricle
• Collects and directs sound
• Primarily cartilage
• External auditory meatus and canal

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OUTER EAR FUNCTION

• Interaural time difference
• Head-related transfer function

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The Human Temporal Bone
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MAMMALIAN MIDDLE EAR

• Increased activity level and metabolism
  development of improved jaw mechanics
• Foreshortened mandible
• Posterior bones became the ossicular chain
• Achieves its major advantage at higher
  frequencies due to middle ear arrangement
• Kangaroo rat (Dipodomys) has middle ear cavity
  larger than its cranial cavity
• Enhances low frequencies re predator avoidance

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MAMMALIAN MIDDLE EAR
http//members.aol.com/tonyjeffs/text/dia.htm
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Evolution of Ossicles in Mammals

• Mandibular joint not between quadrate and
  articular bones
• Now between dentary and squamosum
• Ancient reptilian bones evolved into mammalian
  ossicles
• Articulate bone became malleus
• Quadrate bone became incus
• Stapes evolved from hyomandibular bone (dentary)
• Mammals retain a form of jaw hearing

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The Human Ear Model



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The Canine Temporal Bone
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Avian Anatomy
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Inner Ear
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Inner Ear Bony and Membranous Labyrinth
Bony Labyrinth - channels in temporal bone filled
with perilymph (continuous with CSF) - 3
regions vestibule, cochlea, and semicircular
canals Membranous Labyrinth - series of
membranous sacs and ducts within the bony
labyrinth filled with endolymph
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Mammalian Cochlear Anatomy

• Scala
• Vestibuli
• Media
• tympani
• Basilar Membrane
• Reiseners Membrane
• Modiolis

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The Cochlea in-general

• The actual organ of hearing
• Organ of Corti
• CN VIII
• Cochlear turns vary by organism
• Organ of Corti
• OHC
• IHC

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Cochlear Duct (Scala Media)

• Separated from scala vestibuli by vestibular
  membrane
• Ionic barrier between perilymph and endolymph
• Separated from scala tympani by osseous spiral
  lamina and basilar membrane
• Organ of Corti sits on top of the basilar
  membrane
• Stereo-cilia project from the basilar membrane to
  the tectorial membrane

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The Cochlea
A spiral, bony chamber extending from the
anterior vestibule - contains the cochlear
duct The cochlear duct contains the organ of
Corti (hearing receptor)
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Cochlear Anatomy
Image from http//www.boystownhospital.org/BasicC
linic/neuro/cel/Inside_Cochlea.asp
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The Cochlea
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Cochlear Comparisons
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Avian Cochlear Anatomy
Source ww.bio.purdue.edu/Bioweb/People/Faculty/it
en.html
Source http//www.palaeos.com/Vertebrates/Bones/E
ar/Overview.html
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Resonance of the Basilar Membrane
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The Traveling Wave Tonotopic Organization
From Yost
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The Organ of Corti
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The Organ of Corti
Composed of supporting cells and outer and inner
hair cells, afferent fibers of the cochlear nerve
attach to the base of the hair cells The
stereocilia (hairs) protrude into the endolymph
and touch the tectorial membrane
Bending the cilia opens mechanically gated ion
channels which causes a graded potential and the
release of a neurotransmitter (probably
glutamate) The neurotransmitter causes cochlear
fibers to transmit impulses to the brain
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Hair Cells
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Healthy human ear
High frequency loss Trauma
Photos Natl. Hearing Conservation Assn.
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Metabolic mitochondria lytic mixing
Mechanical stereocilia/plate hair cells/organ of
Corti membranes
Lim in Schuknecht, 1993
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Cochlear Portion of CN-VIII

• Afferent neurons of CN-VIII
• Bi-polar cell bodies
• Spiral ganglion in modiolus
• End-point is dorsal ventral cochlear nuclei
• Efferent neurons
• From dorsal nucleus of trapezoid body
• To dendrites of afferent neurons of OHCs
• Purpose tuning

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The Hearing Threshold Curve
From Yost
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Graphical Hearing Descriptors
Audiogram
Hearing Threshold Curve
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