Auditory And Vestubukar System Flashcards
Difference between vestibular and auditory sensory systems
vestibular senses low frequency (=movement) and auditory senses high frequency (=sound)
- amplitude (volume → dB) & frequency (pitch → Hz)
two relevant measurements for sound?
amplitude (volume → dB):sound,pressure,subjective attribute correlated with physical strength & frequency (pitch → Hz)cycles per second,perceived tone
human range for hearing in each of these parameters?
20-20000 Hz, 0-120 dB
outer ear functions?
capture sound
focus onto tympanic membrane
approx 10 dB amplification of upper range frequencies
protect from external threats
middle ear function?
mechanical amplification (20-30 dB)
inner ear function?
transduce vibration into nervous impulses
Cochlea
Captured rhe frequency and intensity of sound
three compartments of the cochlea?
scala vestibuli → vestibular membrane → scala media → basilar membrane → scala tympani
Scala vestibuli and scala tympani are bone structures which contain peri lymph (high in sodium). Scala mediated is the membranous structure which contains endolymph (high in potassium). Here is where the hearing organ of corti is
what are each filled with? key ingredient in these fillings?
scala vestibuli and tympani → perilymph (high in Na+)
scala media → endolymph (high in K+)
what are each made of?
vestibuli and tympani → bony structures
media → membranous structure with hearing organ (organ of Corti)
where is the organ of Corti and how is it organized
Basilar membrane
Like a xylophone (tonitopically)
narrow and tight base for high frequency, wide and loose apex for low frequency
hair cells pick up signals
cell types within the organ of corti
Inner hair cells and outer hair cells
IHCs carry most auditory nerve afferent information → transduction of sound
OHCs carry most auditory nerve efferent information → modulation of response sensitivity
how does cell depolarisation occur?
tectorial membrane above hair cells causes cell deflection
hairs of the hair cells are called what?
Stereocillia
What does the hair cells deflection do
deflection towards the longest cilium (kinocilium) opens K+ channels
Effect of hair cells and outer deflection
cell depolarisation and subsequent vestibulocochlear nerve depolarisation
what do higher amplitudes do?
cause greater deflection of the stereocilia → more K+ channels open → stronger signalling
deflection in the other direction causes what?
closing K+ channels → hyperpolarisation
vestibulocochlear nerve goes where after cochlea? And what happens next
ipsilateral cochlear nuclei in pons
Superior olive
Inferior colliculus
Medial geniculate body
Auditory cortex
what happens at the level of the superior olive?
some auditory information crossing to the other side → bilateral from this point
- types of hearing loss (anatomical distinction)? associated with issue where?
-
- conductive hearing loss?outer or middle ear
- sensorineural hearing loss (most common)?cochlea or auditory nerve
- central hearing loss?rare, brain/brainstem issue
types of hearing loss (onset distinction)?
sudden hearing loss (minutes to days)
progressive hearing loss (months to years)
causes of conductive hearing loss in (open):
- outer earforeign body, earwax
- middle earotitis, otosclerosis
causes of sensorineural hearing loss in (open):
- inner earnoisepresbycusis (old age degeneration)ototoxicity
- auditory nerveacoustic neuroma (vestibular schwannoma) → unilateral
- tuning fork tests to assess gross hearing loss?
weber test (on skull) and rinne test (next to ear/on mastoid process)
- audiometry signs of conductive/sensorineural hearing loss?
conductive: air conduction hearing much worse than bone conduction
sensorineural: air and bone same, hearing inconsistent between frequencies (some are weaker than others)
a normal threshold is between 0-20dB
what are OAEs?
otoacoustic emissions → normal sounds produced by cochlea used in newborn hearing screening
treatments for hearing loss?
address underlying cause, use hearing aids, cochlear implants and brainstem implants
vestibular system input and output?
input: movement and gravity
output: postural control and ocular reflex
what is the vestibule made up of?
utricle and saccule
These are otolith organs
what else makes up the vestibular system?
three semicircular canals: anterior, posterior, lateral
- utricle
Comnected to ampulla where hair cells sit
- what do the maculae in the utricle and saccule contain?
hair cells, gelatinous matrix, otoliths (carbonate crystals)
what is the orientation in each organ?
horizontally placed in utricle thus detects horizontal movement, vertically placed in saccule thus detects vertical movement
what do the semicircular canals contain?
ampulla contains crista and hair cells, surrounded by cupula to help with movement
rest of canal has endolymph → high in K+
- hair cell resting activity in terms of neural signalling?
they have a basal discharge rate to the nerve
increased by movement of stereocilia toward kinocilium → depolarisation
decreased by movement of stereocilia away from kinocilium → hyperpolarisation
vestibular nerve primary afferents synapse where?
vestibular nuclei in brainstem (pons)
what are the two main vestibular reflexes?
vestibulo-ocular reflex and vestibulospinal reflex
what does VOR do?
Keeps images fixed in retina
by what mechanism does vor workers
vestibular nuclei connected to oculomotor nuclei
eye movement in opposite direction to head movement but same velocity and amplitude
different types of vestibular disorder → how to categorise?
timing (acute/slow onset) and laterality
characteristics of each disorder
acute unilateral main complaints are dizziness, vertigo, nausea, imbalance
slow onset unilateral / any bilateral → main complaints are imbalance and nausea with no vertigo
can also be characterised by location into what? (VD)
peripheral (vestibular organ or vestibulocochlear nerve)
central (brainstem/cerebellum)
Eg peripheral: vestibular neuritis, benign paroxysmal positional vertigo (BPPV), meniere’s disease
central: stroke, multiple sclerosis, tumours
core examination areas for vestibular disease?
Ear eyes legs
red flag symptoms? For vd
headache, gait problems, hyper-acute onset, hearing loss, prolonged symptoms (>4 days)
Exam for acute and intermittent
- acute → vestibular neuritis, strokeHINTS exam
- what is this?head impulse test (horizontal rotational VOR → abnormal usually indicates peripheral issue)nystagmus (repetitive uncontrolled eye movements)test of skew deviation (vertical ocular misalignment → usually absent for peripheral diseases, done by alternate cover test)
- intermittent → BPPVDix-Hallpike test
BPPV pathology?
vertigo on certain maneuvers caused by displaced otolith crystals.
Fixed by epley maneuver
Dix hallpike manouver can help identify
Semi circular canal planes
Anterior and posterior canals form a 90 degree angle
Lateral canals are horizontal to other canals so work in pairs
Vestibular neuritis
Nause and vomiting
Severe vertigo
Nystagmus
Usually due to heroes,epstein barr and influenza virus
Occurs as attacks
Ménière’s disease
Fullness and pressure in ear
Hearing loss
Vertigo
May be due to genetic migraines etc
Nystagmus
Slow phase is where eyes start drifting of away from focus of object
Fast phase is where eyes correct themselves back to original position
Nystagmus named after direction of fast phase
