Mod 12 Hearing and Vestibular System Flashcards
What is the main hearing organ of the ear?
cochlea
What are the names of the fluid in the ear and their locations?
perilymph: surrounds membranous labyrinth
endolymph: fluid inside membranous labyrinth
What is the function of a hair cell in the ear?
will fire if stimulus is strong enough
What are the names of the hair cells and what does the direction of their movement indicate?
kinocilium: tallest hair cell
stereocilium: rest of the hair cells
towards kinocilium: excitation, depolarize
towards stereocilium: inhibition, hyperpolarize
What structures make up the otoliths?
- utricular macula
- saccular macula
What in the semicircular canals detect angular acceleration?
crista ampularis
What direction do the utricular macula detect?
movement in horizontal plane
What direction do saccular macula detect?
vertical orientation
What direction do the semicircular canals detect?
detect any rotational/angular movements
When the semicircular canals are detecting angular movement, what happens on both sides?
one side is excited while the other is inhibited
head to right, right excited, left inhibited
What makes up the peripheral apparatus of the ear?
outer, middle, inner ear
What makes up the central apparatus of the ear?
brainstem, nuclei, pathways, and cortical areas
What are the structures of the outer ear?
- pinna or auricle
- external auditory meatus
What does the external auditory meatus do?
conducts sound to tympanic membrane
What makes up the middle ear?
- air filled space
- tympanic membrane
- oval window
- ossicles: malleus, incus, stapes
- round window
- tensor tympani and stapedius
What makes up the inner ear?
labyrinth
- cochlea
- cochlear duct
- bipolar primary afferents with cell bodies in the spiral ganglion
How much sound is transmitted in by the inner hair cells?
95% of sound
Which part of the cochlea detects high and low frequencies?
high: base
low: apex
What is the function of outer hair cells?
function to influence transduction process in inner hair cells
How does efferent signal to the tectorial membrane influence hearing?
change position of tectorial membrane to make hair cells work better and makes it easier for them to fire (cochlear amplification)
Where do primary afferents of the hearing system reside and do they go?
reside in spiral ganglion, receive input from hair cells, central processes enter the brainstem at the caudal pons
Where do second order neurons of the hearing system reside?
cell bodies located in cochlear nuclear complex of pontomedullary junction
What is the principal ascending auditory pathway and where do most fibers terminate?
lateral lemniscus
terminate at inferior colliculus
Where do third order neurons go in the auditory pathway?
projections from the inferior colliculus and some form the lateral lemniscus form the brachium of the inferior colliculus and project to the thalamus
Where are 4th order neuron cell bodies located and where do they project?
medial geniculate body of thalamus an project as auditory radiation to primary auditory cortex
What do unilateral brainstem lesions do to hearing?
still allow for sound to reach both hemispheres
What do auditory reflexes do?
change sound transmission through the middle ear
What is the purpose of auditory reflexes?
protect the hearing organ and inner ear by a reaction from the stapedius to loud sounds
What is air conduction?
transmission of sound through outer, middle, and inner ears
What is bone conduction?
transmission of sound through just the inner ear and neural pathways
Which is normally greater, air or bone conduction?
air conduction
What is the Rinne test?
hearing test assessing ability to hear a vibrating tuning fork by bone and air conduction
What is the Weber test?
assesses ability to hear vibrating tuning fork equally in both ears
What is an audiogram?
graphic record that charts thresholds of hearing for various frequencies
What is conductive hearing loss?
occurs with lesions of outer and middle ear
- otitis media
- otosclerosis
- built up ear wax
What is sensorineuronal hearing loss?
occurs with lesions of the inner ear or cochlear nerve
- trauma
- anoxia
- infection
- tumor
- inner ear stroke
What are the three key function of the vestibular system?
- motion detection
- maintenance of balance/equilibrium
- gaze stability
What is presbyacusis?
age related changes such as a decreased elasticity of the basilar membrane
What are the three semicircular canals of the ear?
horizontal, anterior, posterior
What does the movement of endolymph in canals do to hair cells?
deflects hair cells
Where do primary afferents of the vestibular pathway reside and where do they terminate?
reside in vestibular ganglia, or ganglia of scarpa
- receive input from hair cells and enter caudal pons
terminate in vestibular nuclei or cerebellum
What are the four pairs of nuclei that make up the vestibular nuclear complex and where is it located?
- superior, lateral, medial, inferior (spinal or descending) vestibular nuclei
in lateral pontomedullar junction
Why are projections of the vestibular system to the cerebral cortex less robust than the auditory system?
because balance is subconscious
What is the role of the lateral vestibulospinal tract (LVST)?
- excitatory to ipsilateral spinal cord nuclei
- facilitates and maintains extensor tone in limbs and trunk
What is the role of the medial vestbulospinal tract (MVST)?
- descend to cervical and upper thoracic spinal cord
- stabilizes and regulates head movements for fixation of gaze
What is the vestibuloocular-MLF reflex?
keeping the head stable during body movement (chicken head)
How is the regulation of extra ocular muscle contraction regulated by vestibular systems?
projections from superior and medial vestibular nuclei project to nuclei of CN III, IV, VI
If you rotate your head to the left which extra ocular muscles are activated and inhibited when keeping your gaze straight?
left medial rectus activates
right lateral rectus activates
opposites are inhibited
What is the pathway of the vestibule-ocular reflex?
scarpa’s ganglion > vestbular nuclei > oculomotor nuclei in brainstem (CN III, IV, VI)
produce compensatory eye movement in plane of stimulated canal
inhibit antagonists
What is vestibular nystagmus?
involuntary, rhythmic deviations of the eyes consisting of slow phase in one direction and fast phase in the other
How is nystagmus named?
always named for fast phase of movement
How is vestibular nystagmus induced?
by deflection of the capula when rotation starts or stops after adaptation has occurred
What is caloric testing?
- method to elicit nystagmus by irrigating th external auditory meatus with warm or cold air/water
What does irrigation during caloric testing do?
causes current in endolymph that activates hair cells
What is an example of nystagmus naming?
cold opposite, warm same (COWS)
What is optokinetic nystagmus and how can it be elicited in clinic?
moving stimuli can elicit reflexive eye movement in patterns of quick saccades
elicited clinically with rotating drum containing vertical stripes
What is a cardinal sign of vestibular dysfunction?
vertigo
What are some autonomic signs of vestibular dysfunction?
nausea, vomiting, pallor, perspiration, blood pressure drop, tachycardia
What is affected in peripheral vestibular disease?
pathology of labyrinth or vestibular nerve
What is affected in central vestibular disease?
pathology of vestibular nuclei, their projections, or central sites of termination
What is benign paroxysmal positional vertigo (BPPV)?
common cause of vertigo due to macular debris being displaced into semicircular canal (posterior most often affected)
When do symptoms occur with BPPV?
rapid changes in head position
How is BPPV diagnosed?
dix-hallpike test (anterior and posterior canals) or supine roll test (horizontal canals)
How is BPPV treated?
treated with series of specific head movements called carnality repositioning maneuvers (CRM)
What is vestibular neuritis?
unilateral peripheral vestibular disorder due to inflammation of vestibular nerve
absent or diminished response to caloric testing of horizontal canal on affected side
what would you expect if someone has vestibular neuritis?
expect positive head impulse test toward side of the lesion
What are the symptoms of vestibular neuritis?
nausea and vomiting which resolve in a few days
What is Ménière’s disease?
episodic syndrome that affects hearing and equilibrium
What are the symptoms of Ménière’s disease?
abrupt attacks and sensorineuronal hearing loss, tinnitus, aural fullness, nausea, and vomiting
What are the central causes of vertigo, nystagmus, and disequilibrium?
ischemic stroke of brainstem or inner ear
cerebellar lesions may directly or indirectly apply pressure on brainstem and vestibular nuclei
