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CHAPTER 15

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  1. CHAPTER 15 Central Auditory Nervous System

  2. Central Nervous System Structures • Nucleus = a group of nerve cell bodies • Fiber Tract = a group of axons

  3. Major Components of the Central Auditory Nervous System (CANS) • VIIIth cranial nerve • Cochlear Nucleus • Superior Olivary Complex • Lateral Lemniscus • Inferior Colliculus • Medial Geniculate Body • Primary Auditory Cortex <Trapezoid Body> Brainstem Mid-brain Thalamus Temporal Lobe

  4. Mid-Saggital View of Brain 4th Ventricle Corpus Callosum Cerebellum Thalamus Pons

  5. MedGen Body • Inf Coll • Lat Lemn • SOC • Coch Nuc • VIIIth CN

  6. Neural Web-Sites http://rprcsgi.rprc.washington.edu/ neuronames/hierarchy.html http://www.ets.uidaho.edu/med532/start.htm

  7. Section Thru Brainstem Shows Cochlear Nucleus

  8. The Superior Olivary Complex

  9. Connections To the Superior Olivary Complex

  10. Superior Olivary Processing Supports Localization • Lateral SO-- Interaural Intensity Differences • Medial SO-- Interaural Time Differences (These are the two primary acoustic cues for localizing sounds)

  11. Dorsal (back) Side of Brainstem • Thalamus (medial geniculate) • Inferior Colliculus • 4th Ventricle • Area of Pons

  12. Inferior Colliculus

  13. Thalamus in Purple

  14. Auditory Radiations Connect • Medial Geniculate Body (in purple) to • Primary Auditory Cortex (in blue)

  15. Lateral-Superior view of brain

  16. Primary Auditory Cortex (AI):superior surface of the temporal lobe

  17. 6 Cortical Layers • Thalamic inputs >IV • project to pyramidal cells in layer III • Divergence from III • within AI • other cortical areas • contra AI • V and VI >>thalamus &IC

  18. Cortical Neurons • Tonotopically and Spatiotopically organized • Highly Adaptable • Sensitive to CHANGES in Frequency and Intensity • Coding virtual pitch • demodulating complex signals (e.g. speech)

  19. Cortical Processing • Pattern Recognition • Duration Discrimination • Localization of Sounds • Selective Attention

  20. Cerebral Dominance/Laterality • Language Processing in the left hemisphere. (Remember the right ear has the strongest connections to the left hemisphere) • Most people show a right-ear advantage in processing linguistic stimuli

  21. Neurophysiological Measures • Gross Evoked Potentials-- Voltage changes in response to auditory stimulation recorded from the scalp • Single-Unit Measures-- Voltage (or other) changes recorded within a neuron

  22. Auditory Evoked Potentials • Recorded in different time intervals (“epochs”) following a sound • Earlier epochs come from lower in the system • Later epochs come from higher in the system

  23. Examples of AEP Epochs • Electrocochleography-- within 5 milliseconds • Auditory Brainstem Response-- thru 10 ms • Middle Latency Response-- thru 75 ms • Auditory Late Response-- thru 200 ms

  24. Auditory Brainstem Response IV V III II I Amp V Amplitude (V) Wave V Latency Time (ms) 10 0

  25. I II III IV V Distal VIIIth nerve Medial VIIIth nerve Cochlear Nucleus Superior Olivary Complex Lateral Lemniscus & Inferior Colliculus GENERATORS of ABR WAVES

  26. Afferent: VIIIth nerve Cochlear Nucleus Superior Olivary Complex Efferent: VIIth nerve nucleus VIIth nerve Stapedius muscle The Acoustic Reflex