Audiology SLP314
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| Vestibular system | Semicircular canals
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| Otolith organs | Utricle. Saccule. (info on linear acceleration, e.g. riding in car or elevator).
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| Internal Auditory Meatus (4) | Canal passageway thru temporal bone, from inner ear to base of brain. Contains: 1. cochlear branch of VIII 2. vestibular branch of VIII 3. Facial nerve VII 4. internal aud. artery (blood supply to cochlea).
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| Cochlear Branch of VIII nerve | Tonotopic organization: Basal fibers (high freq)- outside layer. Apical fibers (low freq)- inside layer.
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| Auditory Nerve | The electrical potentials generated by auditory nerve fibers are called "all-or-none" action potentials because they do not vary in amplitude when activated.
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| Auditory Central Nervous System | Once the action potentials have been generated in the cochlear branch of the auditory nerve, the electrical activity progresses up toward the cortex.
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| Cerebellarpontine angle (CPA) | Point at which VIII nerve-enters brainstem (meeting of cerebellum, pons, medulla). At this level, Cochlear and Vestibular branches separate: -Vestibular branch to cerebellum (helps with balance) -Cochlear branch up through brainstem.
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| Cochlear nucleus (CN) | Auditory nerve (AN) ends here. Tonotopic org. Ipsilateral input from AN. Contralateral output (crossover) to SOC.
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| Auditory Pathways | Ipsilateral pathway (uncrossed). Contralateral pathway (crossed)- Strongest paths- 80% of fibers cross over eventually and reach opposite cortex
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| Consequence of cross-over | above CN - each nucleus receives both ipsi- and contralateral input (sound)
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| Superior Olivary Complex (SOC) | 1.First level for binaural input (1st crossover) 2. Involved in localization in horizontal plane. 3.Binaural process: two ears working together (unilateral loss - can’t localize)
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| SOC localizations | Uses timing and loudness cues: Compares time and intensity between ears. Remember how the Pinna helps to localize: involved in locating height and front vs. back.
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| SOC and reflexes | Acoustic (stapedial) reflex & auropalpebral reflex (babies' eye blink response to loud sounds).
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| Acoustic Reflex | Cochlea - VIII - CN - SOC - motor nucleus of VII - stapedius branch of VII -stapedius muscle. Both stapedius muscles contract when we stimulate one. 10% of population has none. Must use in coordination with other info.
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| Clinical uses of Acoustic Reflex | hearing loss (with other info., i.e. OAE). Detect malingering (incooperation/denial of HL). Assess facial nerve function.
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| Auditory Pathway (7) | Auditory Nerve (AN), Cochlear Nucleus (CN), Superior Olivary Complex (SOC), Lateral Lemniscus (LL), Inferior Colliculus (IC), Medial Geniculate Body (MGB), Cortex (Heschl's gyrus)
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| Lateral Lemniscus (LL) | Nerve fiber tract-runs between SOC and IC
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| Inferior Colliculus (IC) | The last brainstem nucleus (midbrain level at top of BS). Last stage of decussation.
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| Medial Geniculate Body (MGB) | Last subcortical nucleus In the thalamus, major sensory-relay station.
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| Auditory cortex | Heschel's gyrus. Tonotopic org. maintained all the way through cortex.
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| Acoustic neuroma | Benign tumor. 2 sites: internal auditory meatus (common) or cerebellar-pontine angle. 1/1,000 (most over 30). Unilateral (except von Recklinghausen's disease. - bilateral.
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| von Recklinghausen's disease | Bilateral acoustic neuroma.
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| Acoustic neuroma symptoms | Unilateral SNHL. High freqs first (tumor pushes on outer nerve fibers first). Difficulty understanding speech (more than predicted by perception threshold). Sudden worsening of HL (pressure on internal auditory artery) Tinnitus Dizziness (pressure
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