Chapter 11 The Auditory and Vestibular Systems

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Chapter 11 The Auditory and Vestibular Systems

• Outer Ear Vestibular Labyrinth
• Middle Ear Otolith Organs
• Inner Ear Semicircular Canals
• Cochlear Vestibular Pathways
• Auditory Pathways
• Information Encoding
• Primary Auditory Cortex

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I. Outer Ear

• A. Pinna (11.3)
• B. Auditory canal
• C. Tympanic membrane

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II. Middle Ear

• A. Tympanic membrane (11.5)
• B. Ossicles
• 1. malleus
• 2. incus
• 3. stapes
• C. Oval window
• D. Auditory (Eustachian) tube

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II. Middle Ear

• E. Amplification (11.5)
• F. Attenuation reflex
• 1. tensor tympani mus.
• 2. stapedius mus.
• 3. 50-100 msec delay
• 4. Protection
• 5. Filter low frequencies

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III. Inner Ear

• A. Bony labyrinth (11.6)
• 1. vestibule
• 2. cochlea
• 3. semicircular canals
• B. Membranous labyrinth
• 1. saccule utricle
• 2. cochlear duct
• 3. semicircular ducts

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IV. Cochlea

• A. Spiral shape (11.8)
• 1. 2.5 turns
• a. helicotrema
• 2. modiolus
• 3. oval window - scala vestibuli
• 4. Round window - scala tympani

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IV. Cochlea

• B. Chambers (11.7)
• 1. scala vestibuli - perilymph
• 2. scala media - endolymph-hiK
• 3. scala tympani - perilymph
• 4. Helicotrema - continuation of vestibuli
  tympani

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IV. Cochlea

• C. Organ of Corti Structure
• 1. basilar membrane (11.12)
• 2. inner outer hair cells
• a. stereocilia
• 3. tectorial membrane
• 4. nerve endings
• 5. spiral ganglion
• a. bipolar
• 6. supporting cells

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IV. Cochlea

• C. Organ of Corti Structure
• 7. SEM view (11.11)

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IV. Cochlea

• D. Organ of Corti Physiology
• 1. basilar membrane
• a. straightened out (11.8)
• b. response to frequency (11.10)

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IV. Cochlea

• E. Transduction
• 1. movement of stereocilia (11.13)
• 2. directionally selective
• a. depolarization hyperpolarization

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IV. Cochlea

• E. Transduction
• 3. mechanically gated K channels (11.15)
• a. high Ko causes inflow (endolymph)
• b. depolarization
• c. opens v-g Ca channels
• d. exocytosis of synaptic vesicles

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IV. Cochlea

• F. Innervation of Hair Cells (11.16)

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IV. Cochlea

• G. Outer Hair Cell Function
• 1. Cochlear amplifier (11.17)

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V. Auditory Pathways

• A. VIII n (11.18)
• B. Medulla
• 1. cochlear nuclei
• C. Superior olive
• 1. lateral lemniscus
• D. Bilateral
• E. Variations

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V. Auditory Pathways

• F. Inferior colliculus (11.18)
• G. Thalamus
• 1. medial geniculate nucleus
• H. Primary auditory cortex
• 1. transverse temporal gyri
• I. Association auditory cortices

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V. Auditory Pathways

• J. Efferents
• 1. Olivocochlear bundle
• a. superior olive
• b. to outer hair cells
• (11.16, 11.18)

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V. Auditory Pathways

• J. Efferents
• 3. Attenuation Reflex
• a. superior olive
• b. VII n.
• c. tensor tympani stapedius muscles
• (11.18, 8.10a, see also p. 234 for ventral view
  of brain)

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V. Auditory Pathways

• K. Conduction Deafness - external middle ear
• 1. Tuning fork test
• a. air conduction - no
• b. bone conduction - yes
• 2. Causes
• a. obstruction of external auditory meatus
• b. thickening of tympanic membrane
• c. chronic otitis media
• d. obstruction of the eustachian tube
• 3. Surgically corrected

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V. Auditory Pathways

• L. Nerve Deafness
• 1. Cochlea
• 2. VIII n
• M. Central Deafness
• 1. Rare since pathway is bilateral

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VI. Information Encoding

• A. Characteristic frequency (11.19)
• B. Tonotopy - map of basilar membrane (11.21)
• C. Intensity
• 1. AP frequency
• 2. number of axons

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VI. Information Encoding

• D. Sound localization in horizontal plane
• 1. interaural time delay (11.23)
• 2. interaural intensity difference (11.24)

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VII. Primary Auditory Cortex

• A. Acoustic radiation
• B. A1, Brodmanns area 41, 1o auditory cortex
• C. Columnar tonotopic map (11.29)
• 1. parallel processing
• D. Binaural, ear preference

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VIII. Visual vs. Auditory Pathways

• A. Differences B. Similarities

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The Vestibular System

• Vestibular Labyrinth
• Otolith Organs
• Semicircular Ducts
• Vestibular Pathways

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I. Vestibular Labyrinth

• A. Bony labyrinth (11.31b)
• 1. Vestibule
• 2. Three Semi-circular canals
• 3. Perilymph

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I. Vestibular Labyrinth

• B. Membranous labyrinth (11.31a)
• 1. Saccule
• 2. Utricle
• 3. Semicircular
• ducts
• 4. Endolymph

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II. Otolith Organs

• A. Two Maculae (11.32)
• 1. Epithelium
• a. hair cells
• b. supporting cells
• 2. Otolithic membrane
• 3. Otoliths
• 4. Nerve terminals

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II. Otolith Organs

• B. Function (11.32)
• 1. Kinocilia
• 2. Direction selective
• 3. Linear movement, gravity

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III. Semicircular Ducts

• A. Three Ampullae (11.31a)

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III. Semicircular Ducts

• B. Three Cristae ampullares (11.34a)
• 1. Epithelium
• a. hair cells
• b. supporting cells
• 2. Cupula
• 3. Nerve terminals

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III. Semicircular Ducts

• C. Function (11.34b)
• 1. Kinocilia
• 2. Direction selective
• 3. Rotation, acceleration

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IV. Vestibular Pathways

• A. Medulla
• 1. Vestibular nuclei (11.36)
• a. spinal cord motor neurons - posture
• b. thalamus - somatosensory ctx, motor ctx
• c. oculomotor control -
• III, IV, VI
• d. cerebellum -
• motor coordination

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IV. Vestibular Pathways

• B. VOR-stable vision during head movement