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Inner Ear Anatomy and Physiology

This text provides an overview of the anatomy and physiology of the inner ear, including the bony and membranous labyrinth, cochlea, utricle, saccule, and semicircular canals. It also discusses the role of hair cells and fluid mechanics in balance and hearing, as well as common pathologies and their treatments.

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Inner Ear Anatomy and Physiology

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  1. Anatomy and Physiology

  2. Inner ear • Consists of: • Bony labyrinth • The tubes and chambers within the petrous portion of the temporal bone • Membranous labyrinth • The functional part of the vestibular apparatus. 3 portions • Cochlea – has little input into balance. The main hearing apparatus • 2 large chambers, the saccule and the utricle – these are the main balance apparatus • 3 semicircular canals – useful for detecting rotation, also vital in maintaining balance

  3. Utricle and Saccule • Chambers containing a small sensory area known as the macula • Maculae • This consists of thousands of hair cells which, as well as synapsing with the vestibulocochlear nerve at their proximal end, project into a gelatinous layer covering the maculae. The gelatinous layer has many tiny calcium carbonate crystals (otoliths) embedded in it. It is the difference between the specific gravity between these crystals and the surrounding fluid (endolymph) that bends the hair cells to produce signals regarding position.

  4. Semicircular canals • Function by different mechanism • Do not contain otoliths • Works by the presence of enodolymphatic fluid within the chambers flowing through the canals in response to movement. Hair cells within ampullae of the canals will bend with the flow of liquid, producing signals.

  5. Movement is detected by hair cells • 2 types of hair cells • Type 1 detects head movement • Type 2 detects linear acceleration • Travels via CN VII to brainstem nuclei • Important reflexes are elicited • Vestibuloocular reflex (VOR).....this stabilizes images on the retina during head movement by producing an eye movement in the direction opposite to the head movement, therefore preserving the image in the centre of the visual field • VST • VCT

  6. Causes of pathology Important to differentiate: • Central • Presence of focal neurology, cerebellar signs, eye problems, LOC, weakness • Peripheral • Ear symptoms, abnormal Rinne or Weber

  7. Central disease • Cerebrovascular disease • Cerebellar stroke • Vertebrobasilar insufficiency • Acoustic Neuroma • Vasculitis • Migraine • Demyelination (MS)

  8. Peripheral Disease • Labyrinthitis • Acute vertigo sometimes associated with nausea, vomiting and ataxia “world shakes up and down when I walk”. Often spontaneously resolves over several days • Benign paroxysmal positional vertigo • Caused by otoliths ending up in the semicircular canals, inappropriately activating the hair cells there. Acute episodes of short lived vertigo • Menieres Disease • Triad of vertigo, sensorineural deafness and tinnitus. Unknown cause, attacks last from a few hours to several days. Usually remits after several years. • Otitis • Ototoxicity • Frusemide, gentamicin, NSAIDS, quinine

  9. Treatment • General treatment for vertigo • Disease specific

  10. General • Symptomatic • Vestibular rehabilitation

  11. Symptomatic treatment • Best for acute episodes, but not for very brief, i.e. BPPV • Antihistamines.....Drug of choice • Meclizine, diphenhydramine • Phenothiazine antiemetics....if severe vomiting. Beware of sedation • Prochlorperazine, domperidone, metoclopramide • Benzodiazepines.....reserved for those with contraindications to anticholinergics, i.e. prostatism and glaucoma • Should be stopped as soon as vomiting ceases

  12. Vestibular rehabilitation • Better for peripheral injury • Total recovery comes from central nervous system compensation • Activities promotes adaption, strategic substitution and prevents negative effects such as deconditioning • Evidence more effective if commenced early • Different types • Acute peripheral....focusing on object with blank background • Chronic peripheral......eye and head movements – more aggressive • Bilateral vestibular loss.....saccadic eye exercises and neck exercises • Central....gait and balance activities • Ask your local physio!

  13. Disease specific • Peripheral • Central

  14. Peripheral • Labyrinthitis • Corticosteroids in acute period • BPPV • Diagnosed with Hallpike, treated with Epley manoeuvre • Menieres • Patient education • Lifestyle adjustments • Salt restriction, caffeine + nicotine avoidance, stress relief, limit alcohol to one drink per day • Diuretics and betahistine.........? Efficacy • Interventional • Intratympanic gent....low dose may not cause deafness • Vestibular neurectomy...craniotomy. Relieves 90% of vertigo, 10-20 % hearing loss • Labyrinthectomy....results in deafness • Shunting

  15. Otitis • Antibiotics, analgesia, antiemetics • Ototoxicity • Abstinence

  16. Central • CVA (posterior circulation/ vertebrobasilar insufficiency) • Vascular • Acoustic neuroma • ENT referral and removal • Vasculitis • Steroids • Migraine • Analgesia • Demyelination • Steroids, interferon

  17. Hallpike manoeuvre (It should work if you click on it and wait for a couple of seconds!)

  18. Epley manoeuvre

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