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Overview of the Central Auditory Nervous System and Its Major Components

This chapter explores the Central Auditory Nervous System (CANS), detailing its key components, including the VIIIth cranial nerve, cochlear nucleus, superior olivary complex, lateral lemniscus, inferior colliculus, medial geniculate body, and primary auditory cortex. It discusses how the auditory pathways process sound localization cues and the organization of cortical neurons. The chapter further examines neurophysiological measures, such as auditory evoked potentials, and their importance in understanding auditory processing, language dominance, and the brain's response to auditory stimuli.

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Overview of the Central Auditory Nervous System and Its Major Components

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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

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