Auditory and Vestibular Systems I&II Flashcards
what is amplitude (loudness) measured in?
decibels (dB)
-sensitivity is inconsistent
what is wavelength (frequency) measured in?
hertz (Hz)
- normal range 20-20000 Hz
- sensitive to 1000-3000 Hz to detect human voices
outer ear
pinna (funnel) and auditory tube (canal)
- where foreign bodies are located
- contain air
middle ear
amplifies sound; deep surface of tympanic membrane
- malleus, incus, stapes
- contain air
- tensor tympani attaches to malleus - innervated by trigeminal (mandibular branch)
- stapedius - facial nerve
- limit vibratory capacity by contracting tensor tympani and stapedius
inner ear
contains cochlea - converts sound from air into liquid and contains afferent fibers
- cells convert waves in liquid into electrical signals
- higher frequencies –> narrow region near base
- lower frequencies –> wider region near apex
organ of corti
contains inner and outer hair cells
-also supporting cells
role of kinocilium and stereocilia
project into endolymph turning wave signals into electrical signals
endolymphatic hydrops
too much perilymph
associated with Meniere’s disease
inner vs. outer hair cells
inner - perceive sound, high sensitivity
outer - amplify sound wave propagation, can be killed by prolonged ototoxic drugs/antibiotics –> hearing loss
otoacoustic emissions
sound travels from cochlea to auditory canal (reverse)
-tests auditory ability
ascending hearing pathway
- inner hair cells –> spiral ganglion by CNVIII –> cochlear nuclei (1st synapse) –> superior olivary nucleus –> inferior colliculus (2nd synapse) –> auditory cortex
- left and right auditory cortices ALWAYS receive input from BOTH ears
- contralateral or ipsilateral fibers
auditory cortex frequencies
- high frequency sounds - processed more medially, deeply
- low frequency sounds - processed more laterally, superficially
brodmanns areas
- 41,42 = basic properties, detect thunder from gun shot
- 22 = pitch, intensity, emotion - pick up tone, sarcasm
descending hearing pathways
- lateral olivocochlear efferents –> inner hair cells (go through spiral ganglion)
- medial olivocochlear efferents –> outer hair cells (bypass spiral ganglion)
hearing reflex - ways to decrease volume
- contract stapedius or tensor tympani –> dampen sustained loud noises
- can also dampen with outer hair cells
hearing disorders
- hypoacusis = decreased hearing
- hyperacusis = increased hearing
- deafness = loss of hearing
- hallucinations
- neuroma
- tinnitus = hear sound with no sound present
acoustic neuroma aka vestibular schwannoma
benign tumor on cranial nerve VIII
-tinnitus, loss of hearing, dizzy
conductive hearing loss
- outer ear - foreign body
- middle ear - dysfunction of auditory ossicles, fluid accumulation –> upper respiratory tract inflammation
sensorineural hearing loss
dysfunction of hair cells
- CNVIII works fine
- treat with cochlear implants
presbycusis
hearing loss due to aging
where does sound/hearing occur?
cochlea
where does balance occur?
saccule, utricle, cristae of semicircular ducts
vestibule system
- contains otolith organs - utricle and saccule
- contain semicircular canal
- suspended in perilymph - bony labyrinth
what is affected by stapes induced pressure changes?
the cochlea, not the vestibular apparatus
role of the cupulla w/I the ampulla
contains receptor and supporting cells
-rotation –> endolymph stagnant and displace semicircular canals –> deflect cupula and detracted by receptor cells
semicircular duct
detect angular or rotational movement
utricle
detect linear movement (side to side)
- macula inferiorly
- stereocilia superiorly
saccule
detect linear movement (vertical)
- macula medially
- stereocilia laterally
otoconia
in saccule and utricle
- switch positions with linear movement
- continued stimulation of hair cells in absence of semicircular duct (acceleration)
ascending vestibular pathway
vestibular nuclei - input from accessory optic nuclei –> no change in gate if damaged
descending vestibular pathway
vestibular nuclei transmit info to:
- cranial nerves 3,4,6 –> extra ocular muscles
- MVST –> CN11 –> head and upper body
- LVST –> lower limbs
- MLF –> connection b/w extra ocular muscles and MVST
3 types of info. go to vestibular system
- eyes, inner ears, proprioception
- loss of 2 –> lose balance, dizzy, vertigo
- overseen by cerebellum
vestibulo-ocular reflex
turn head to left and eyes pull back toward right
- ex. excitation increases contraction of right lateral rectus and left medial rectus
- more affective than visual tracking
damage to medial leminscal pathway vs. cerebellar damage
Romberg test
- DML –> lose balance when closing eyes, loss of proprioception
- cerebellar –> lose balance with eyes open
nystagmus
normal - visual tracking
abnormal - vestibular dysfunction (CN8) –> dysfunctional tracking
vertigo
positional hallucinations - loss of balance
-can be caused by acrophobia and can cause vestibular dysfunction
benign paroxysmal positional vertigo
forceful head movement dislodges otoconia –> vertigo when head is in a certain position
alcohol effects on vestibulocochlear system
infiltrates cupulae faster dropping density –> hair cells move quicker
- spinning room (overly sensitive to movement)
- rebound effect - alcohol leaves cupulae raising density and decreasing hair cell movement –> exaggerate movement
- gate compromised
alcohol effect on stapedius and tensor tympani muscles
reduces contraction of muscle increasing the sensitivity to sound (muscle tone relaxant)
