1b// The Auditory System Flashcards
What do vestibular and hearing organs do?
Vestibular organ: capture low frequency motion (movements)
Hearing organ: capture high frequency motion (sound)
What cells do cochlea and canals come from?
stotocyst
What is frequency/ pitch (Hz)?
cycle per second, perceived tone
What is amplitude/ loudness (dB)?
Sound pressure, subjective attribute correlated with physical strength
What is the humans range of hearing?
Frequency: 20–20,000Hz
Loudness: 0 dB to 120 dB sound pressure level (SPL)
What are the outer ear functions?
To capture sound and to focus it to the tympanic membrane.
Modest amplification (10DB) of upper range of speech frequencies by resonance in the canal.
To protect the ear from external threats.
What is the function of the middle ear?
The main function of the middle ear is mechanical amplification (can provide an additional 20-30dB)
What is the hearing part of the inner ear?
cochlea
What is the function of the cochlea/ inner ear?
Its function is to transduce vibration into nervous impulses
It does so in a way that captures the frequency (or pitch) and intensity (or loudness) of the sound
How many compartments in the cochlea? And what are they?
3
scala vestibuli
scala tympani
scala media
What are the scala vestibuli and scala tympani?
Bone structures, contain perilymph (high in sodium)
What is the scala media?
Membranous structure, contains endolymph (high in potassium). Here is where the hearing organ or Organ of Corti is located.
*depending on frequency it will go through media at a certain point
What lies in the basilar membrane?
the organ of Corti
How is the basilar membrane arranged?
Basilar membrane is arranged tonotopically, using the same principle as a xylophone
What is the hearing organ?
the organ of corti
What does the organ of corti contain?
1) Inner hair cells (IHC) and
2) Outer hair cells (OHC)
What is above the hair cells?
tectorial membraine
What does the tectorial membrane do?
allows hair deflection, which in turn will depolarise the cell.
What do inner hair cells do?
IHC carry 95% of the afferent information of the auditory nerve. Their function is the transduction of the sound into nerve impulses.
What do outer hair cells do?
OHC carry 95% of efferents of the auditory nerve. Their function is modulation of the sensitivity of the response.
What are the hairs of the hair cells called?
stereocilia
What is the longest stereocilia called?
kinocilium
How do stereocilia work and what do they do?
The deflection of the stereocilia towards the longest cilium (kinocilium) will open K+ channels (influx of K+)= depolarisation
This depolarises the cell releasing the neurotransmitter to the afferent nerve which then depolarises.
Higher amplitudes (louder) of sound will cause greater deflection of stereocilia and K+ channel opening
AKA TRANSDUCTION
*away from kinocilium= hyperpolarisation
WHat causes depolarisation and hyper-polarisation in transduction? (ion wise)
depolarisation= open K+
hyper= closes k+
Describe the differences between IHC and OHC.
- arrangement
- contact with tectorial membrane
- carries what info
- function
Describe the auditory pathways.
Spiral ganglions via the vestibulo-cochlear nerve (CN8) travel to the ipsilateral cochlear nuclei (monoaural neurons) in the brainstem (pons)
Auditory information crosses at the superior olive level
After this point all connections are bilateral
What are the types of hearing loss?
conductive hearing loss
sensorineural hearing loss
central hearing loss
sudden or progressive hearing loss
What is the difference between sudden and progressive hearing loss?
Sudden hearing loss minutes to days
Progressive hearing loss months to years
What is conductive hearing loss?
problem is located in outer or middle ear
What is sensorineural hearing loss?
the sensory organ (cochlear) or the nerve (auditory nerve)
90% of all hearing is lost
What are causes of conductive hearing loss?
outer ear= wax, foreign body
middle ear= otitis, otosclerosis
What is otitis?
Bubbles can be seen through the ear drum, suggesting there is liquid inside the middle ear.
due to inflammation/ infection (bac or viral)
What can you use to see inside the ear?
otoscope
What is otosclerosis?
formation of new bone around the base of the stapes
aka extra bone, it is progressive and common in young women
What are causes of sensorineural hearing loss?
inner ear= noise, presbycusis, ototoxicity
nerve= acoustic neuroma (vestibular schwannoma) (unilateral)- can press on CN8
What are clinical bedside tests for hearing?
whisper in ipsilateral ear whilst rubbing fingers in contralateral ear
tuning fork (weber and rinne test)= assesses the presence of gross hearing loss
What is an audiogram? And what does hearing loss look like in one?
The audiogram is where the hearing thresholds are plotted to define if there is a hearing loss or not. A normal hearing threshold is located between 0 – 20dB
the decibels are going up to be heards headphones that make a clicking sound, can also put on mastoid
What do conductive and sensorineural hearing loss look like in audiometry?
*normal for conductive hearing loss when its bone conduction
What type of sound does the normal cochlea produce?
The normal cochlea produces low-intensity sounds called Otoacoustic Emissions (OAEs)
What specific cells produce Otoacoustic emissions (OAEs) and when?
These sounds are produced specifically by the outer hair cells as they expand and contract
How can hearing loss be monitored on new borns?
otoacoustic emissions (OAEs)
This test is often part of the newborn hearing screening and hearing loss monitoring.
What is the treatment for hearing loss? (4)
underlying cause
cochlear implants
hearing aids
brianstem implants
