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Transcript
Cell Types and Physiology in the CANS Major Components of the Central Auditory Nervous System (CANS) • • • • • • • VIIIth cranial nerve Cochlear Nucleus Trapezoid body Superior Olivary Complex Lateral Lemniscus Inferior Colliculus Medial Geniculate Body Primary Auditory Cortex Brainstem Mid-brain Thalamus Temporal Lobe • • • • • • MedGen Body Inf Coll Lat Lemn SOC Coch Nuc VIIIth CN VIIIth Nerve Afferents Time (ms) 40 36 32 28 24 20 Sound Off 16 12 8 Sound On 4 35 30 25 20 15 10 5 0 0 – AVCN – PVCN – DCN AP Rate • Bipolar Neurons • Primary Response Type 50 45 • Synapse in: 40 Section Thru Brainstem Shows Cochlear Nucleus Cochlear Nucleus • • • • Wide variety of cell types AVCN >>to ipsi and contra SOC PVCN >>to contra Lat. Lemniscus & IC DCN>>contra to Lat Lemniscus CN Response Types • Primary-like cell- spherical (bushy) cells of the AVCN • Chopper cell- identification with any particular cell type is not possible because responses are found throughout the cochlear nucleus • Onset- located in octopus cells • Pauser cell/ Build up cell- located in the fusiform layer of the DCN Pauser cell Primary-like cell Onset cell Buildup cell CN Response Types Chopper cell DCN Networking • Intranuclear connex – (largely inhibitory) – Enhancing tuning? • Outputs rising in lateral lemniscus – Predominantly contralateral The Superior Olivary Complex Connections To the Superior Olivary Complex 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) SOC Physiology • Lateral SOC (EI and predominantly high freq) – Max Response to large SPL diffs between ears – Equal SPLs produce little activation – Larger in animals with smaller heads • Medial SOC (predominantly EE and low freq) – Max Response to specific interaural time diffs – Larger in man than in animals with smaller heads Interaural Delay affects MSO Synchronous Firing Rate 8 Spikes/Cycle 7 6 5 700 Hz 1300 Hz 4 3 2 1 0 -1.6 -1.2 -0.8 -0.6 -0.4 -0.2 0 0.2 Time Diff Between ears (ms) 0.4 0.8 0.35 0.3 Spike %age 0.25 0.2 0.15 Ipsi 0.1 Contra 0.05 0 0 0.3 0.5 0.7 % of Cycle 0.9 Lateral Lemniscus • Tract of axons from just above SOC to IC (originating from cell bodies in several different structures) • Has a Nucleus (Nucleus of LL) – Good Temporal Resolution • Involved in Startle Reflex – Connection from CN to Pontine Reticular Formation – PRF >>motor neurons and spinal interneurons Dorsal (back) Side of Brainstem • Thalamus (medial geniculate) • Inferior Colliculus • 4th Ventricle • Area of Pons Inferior Colliculus Inferior Colliculus • Cells respond to characteristic: – – – – Interaural delays Interaural amplitude differences Amplitude modulations Frequency modulations • Integration of multi-modal sensory inputs – – – – Adjacent visual nuclei Proprioception of head and neck Outputs include oculomotor nuclei IC stim modifies activity in brain areas involved in attention and learning. Medial Geniculate Body Thalamus • Last Sensory Relay Station prior to Cortex • Complex of nuclei • MGB is mainly auditory – But has other inputs as well – AND – Some other nuclei respond to aud. stim. MGB • Three Sub-divisions: – Ventral MGB – True Auditory Relay nucleus – Medial MGB – Auditory with Somatosensory – Dorsal MGB –Somatosensory Ventral MGB: • Relay cells with overlapping dendritic “nests” • Interneurons inhibit relay cells & other interneurons • Tonotopic Lows-lateral, highs-medial. • Most (90%) Cells are binaural (EE or EI) • 10% Monaural cells: contralateral excitation Medial MGB: • Cells have CF, – Some show broad tuning – Some have TWO CFs • “Characteristic Intensity” in some cells • EE, EI, IE • All respond for duration of stim – Little Adaptation – But show Habituation • Influenced by somatosensory inputs Dorsal MGB • Inputs – From IC Both Aud. & Mixed – From Superior Colliculus – Somatosensory Afferents • “Nonspecific” responses Auditory Radiations Connect • Medial Geniculate Body (in purple) to • Primary Auditory Cortex (in blue) Primary Auditory Cortex (AI): superior surface of the temporal lobe 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 Cortical Neurons • Tonotopic – Lows lateral – Highs medial • Spatiotopic – (best responses from contralateral hemifield) • Strong Habituation/Learning • Sensitive to CHANGES in Frequency and Intensity Cortical Processing • • • • Pattern Recognition Duration Discrimination Localization of Sounds Selective Attention Cerebral Dominance • Most right-handed individuals show distribution of 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