Hearing, Vertigo, ETC... Flashcards Preview

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Flashcards in Hearing, Vertigo, ETC... Deck (55)
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Sections of Normal Ear



Transduction of Sound

-sound waves propagate in air, enter external auditory canal & bounce off tympanic membrane
-membrane moves malleus, incus, & stapes
-stapes mov. changes the pressure in the fluid filled inner ear and that triggers wave in the basilar membrane of the cochlea
-hearing by bone conduction: bone transmits vibration


Transduction of Sound: at Cochlea

-hair cells with stereocilia are found in the organ of Corti, which rests on the basilar membrane
-hair cells are in contact with the tectorial membrane and are deformed by the traveling wave of sound
-high frequency tones maximally displace the basilar membrane near the base of the cochlea
-as freq. of sound dec., the point of maximal membrane displacement moves toward the cochlear apex
-distortion of the stereocilia on the hair cells causes depolarization of the cell & that results in inc. electrical activity along the auditory nerve


Hearing Loss

-Very common
-all ages
-1/1000 children: sig. hearing loss
-10% of population has some hearing loss
-will inc. as population ages


Causes of Conductive Hearing Loss

-transmission of sound through air is blocked
-may diff. causes: ear wax, foreign object in ear canal, otitis externa, tympanic membrane perforation, otitis media with effusion, otosclerosis


Sensorineuroal Hearing Loss

-Disorders of the cochlear nerve, central pathways
-prebyacusis - age related
-viral - mumps, measles, rubella, CMV, HIV
-ototoxicity: drugs
-meniere's disease
-vestibular Schwannomas (acoustic neuroma)


Mixed Hearing Loss

-Otosclerosis involving the ossicles & the cochlea
-transverse & longitudinal temporal bone fx
-head trauma
-chronic otitis media
-cholesteatoma & middle ear tumors
-some inner ear malformations


Meniere's Disease

-dilated membranous labyrinth (hydrops)
-produces vertigo, fluctuating sensorineural hearing loss & tinntius
-dec. resorption of endolymaphatic fluid causes build-up or hydrops with high pressure, bowing & subsequent rupture in the membranse separating the endolymph from the perilymph
-30min to several hrs until equilibrium is reestablished
-hearing loss persists & gradually worsens
-Treatment: low salt dies & diuretics can be helpful


Clinical Assessment of Hearing Loss

-constant, progressive, fluctuating
-ear discharge
-tinnitus, vertigo
-family history - otosclerosis


Hearing Loss Examination

-pinna (deformity)
-external auditory canal (obstruction)
-tympanic membrane
-middle ear space (aerated)
-pneumatic otoscopy
-Weber & Rinne


Rinne Test

-tell whether air conduction is greater than bone conduction
-normal: patient should hear sound in air after bone stops


Weber Test

place on patients forehead
-if conductive hearing loss: sound will lateralize to that ear


TM Perforation

-common & usually a consequence of infection
-trauma, including barotrauma, can perforate the membrane wall
-deg. of hearing loss depends on the size of hole



-growth of abnormal bone around the otic capsule leads to fixation of the stapes resulting in a conductive hearing loss
-often accompanied by progressive sensorineural component
-starts in 20s to 30s and is bilateral
-family history +
-treatment is observation, hearing aid, or stapedectomy


Vestibular Schwannomas

-Schwann cells, former designation of the tummor is preferable
-Meningiomas also occur in this spot
-present with sensorineural hearing loss & not with vertigo
-compression of the eight cranial nerve is so slow & gradual that the brain has adequate time for central compensation when the vestibular input dec. on one side
-by blocking visual fixation & provoking the semicircular canals, still detect the vestibular abnormality but that is a topic covered in a separate module on vertigo



-20% elderly patients experience is once a year that restricts activity & prompts physician visit
-Presyncope (faintness, lightheadedness)
-loss of balance, unsteadiness of gait
-Vertigo (spinning, swaying, illusion of movement)
-double vision, psychological dissociative feelings, vague sensations (hypoglycemia; drug intox. giddiness)


Dizziness from Orthostatic Hypotension?

-lower body venous pooling (prolonged squatting)
-IV volume depletion
-medication effect
-autonomic neuropathy

-vasovagal reaction (neurocardiogenic syncope)


Dizziness from Heart Diseases?

-ones that dec. cardiac output

-cardiac arrythmia
-congestive heart failure
-obstructed cardiac outflow (aortic valvular stenosis, cardiac tamponade, idiopathic hypertrophic subarotic stenosis (IHSS))
-pulmonary embolism


Gait Imbalance in the Elderly

-neuronal loss due to aging or disease in networks that sub serve:
cerebellar function (stroke, alcoholism)
vestibular function (prior head trauma)
visual orientation (cataracts)
peripheral nerve function (position sense in legs)


Elderly "Dizzy when I walk"

-neuronal loss due to aging or disease in networks that subserve: motor strength (stroke, cervical spondylosis), frontal lobe apraxia, basal ganglia (Parkinson's, Lewy body dis, PSP, MSA), Arthritis & pain (hip & knees), inactivity & fear of falls

-drug toxicity & dehydration


Psychiatric "Disassociation"

-feels distant from the real world
-home stressors
-past/current depression, panic attacks, anxiety, neurosis, psychosomatic personality
-family history of psychiatric disease
-hyperventilation for 3 min to reproduce symptoms (may activate seizure focus)
-neuropsych eval. Minnesota Multiphasic Personality Inventory (MMPI) detects somatization tendencies
-consult psychiatry


"True" Vertigo

-Disease of vestibular system (central & peripheral)
-illusion of movement (whirling, spinning, swaying)
-often accompanied by nausea & vomiting
-Nystagmus (clinical sign): fast & slow components, defined by fast component (saccade), brain suppresses visual blur during saccade, vision possible only during slow phase of eye movement, room spinning to right to slow phase to left



-spin around the z-axis


Specialized Vestibular "organs" act as motion transducers for?

-Translational motion (linear around x, y, z)
-Rotational motion (angular around x, y, z)


How does the vestibular system monitor position?

-detecting angular (rotational), static & linear acceleration with specialized motion detectors



-coplaner with the vertical axis
-detect static head positions & linear accelerations in plane



-coplaner with the horizontal axis
-detect static head positions & linear accelerations in plane


What does the ampulla detect?

-rotational acceleration or deceleration within the plane of the canal



-located inside ampulla transduce this information for each semicircular canal



-tallest cilia in ear
-depending on how it's bent, potassium channels in the tips of other cilia either open or close
-cilia project into endolymph that is rich in potassium, K influx depolarizes the cell membrane which then activates Ca channels that open only when the membrane is depolarized
-Ca influx activates Ca dep. K pumps that extrude the K into the K poor perilymph
-allows for electrical resonance of the membrane to shift up or down in frequency & to modulate the conc. of Ca at the hair cell base
-a rise in local Ca conc. triggers release of neurotransmitter