Auditory and Vestibular system Flashcards
What are the anatomical regions of the ear and what are their functions?
Outer ear- capture sound and focus it to tympanic membrane. increase amplification
Middle ear- mechanical amplification via ossicles
Inner ear- cochlea turns mechanical sound to neural signal via the endolymph fluid which moves according to the wave sound it receives from the ossicles
What are the compartments of the cochlea? and what is the physiology?
Scala vestibuli and scala tympani which are bone structures containing peri lymph (high in Sodium)
Scala media which is a membranous structure containing endolymph containing the hearing organ or organ of corti (high in Potassium)
What is the basilar membrane and what does it do?
Where is it located?
located in the Scala media sub to the organ of corti, detects movement of endolymph and causes hair cells to move according to the frequency is receives
arranged tonotopically
What is the organ of corti?
What hair cells are located on the organ of corti? What lies above them and what does it allow?
It’s the hearing organ
Inner hair cells (IHC)- transduction of sounds into nerve impulses to brain (afferent)
outer hair cells (OHC)-modulate sensitivity of response (efferent) towards ear
above lies the tectorial membrane and allows hair deflection to depolarise the cell
What is the physiology and mechanism of auditory hair cells?
How does transduction happen?
How does a higher amplitude affect deflection of stereocilia?
located at the organ of corti are the stereocilium with the kinocilium being the longest. if these cilia move towards kinocilium it causes an influx of potassium (deflection) = depolarisation = Ca2+ influx = glutamate released from exocytosis to afferent nerve in perilymph
Perilymph is connected to CSF (access to brain)
Higher amplitudes will cause greater deflection of stereocilia and more potassium influx
What is the auditory pathway once the mechanical sound turns to neural?
cochlear/auditory nerve joins 8th cranial nerve vestibulo-cochlear nerve into brainstem and cortex (temporal lobe)
What are the different types of hearing loss?
Which is most likely?
Conductive: problem located in outer or middle ear
Sensorineural: sensory organ (cochlea) or nerve (auditory nerve) damage
Central: brain and brainstem
Sensorineural is most common (90%)
Describe the inner ear anatomically
Describe the cochlea anatomically
What are causes for each type of hearing loss?
Conductive: wax, foreign body, otitis (bubbles in middle of ear), otosclerosis (extra bone formation in middle ear)
Sensorineural: too much loud noise damage, ototoxicity
(Toxicity due to things eg ABs), neuroma (auditory nerve)
What are the clinical investigations for hearing?
What is an audiometry?
Weber test (middle of head should sound even) and Rinne test (mastoid) use a tuning fork to assess gross hearing loss
Whisper in ipsilateral ear (check if they can hear this) whilst rubbing fingers in contralateral ear (to distract this ear)
Audiometry: checks pattern of hearing thresholds to check if there’s a hearing loss or not
What are the treatment options for hearing loss?
Treat underlying cause eg remove wax or treat infection (otitis)
Cochlear implants
Hearing aid
Describe the anatomy of the vestibular organ, particularly the utricle and saccule
What does the vestibular organ do?
Detect and inform head movements and its speed of movement so it can stabilise accordingly, balances us
There is the utricle and saccule have maculae and therefore hair cells and otolith on top.
These detect movement
There are also 3 semicircular canals with ampulla’s on one side of each, they are connected to the utricle
What kind of organs are the saccule and utricle?
What plane are their maculae positioned in?
What movements do they each feel respectively?
What specific membrane moves when these movements occur?
Otolith organs
Utricle- horizontally: feels horizontal movement of head
Saccule-vertically: feels vertical movement of head
Otolith (on top of hair cells causing them to move)
What is the anatomy of the semicircular canals?
What are the three planes and what movements do they each detect?
Hair cells located in crista, inside ampulla
Rest of canal has endolymph- liquid high in potassium
Anterior: saying yes
Posterior: head tilt from one shoulder to the other
Lateral: saying no
How is a depolarisation and hyperpolarisation of hair cell happen in the crista?
What do they cause neurally?
A depolarisation is caused by the hair cells moving towards the kinocilium (as a result of the endolymph fluid when we move our head) and therefore a nerve discharge
Hyperpolarisation is the opposite and inhibits a nerve discharge
