auditory system Flashcards
do vestibular organs capture low or high freq motion?
they capture low frequency motion (movements)
do hearing organs capture high or low freq motion?
high frequency motion (sound)
evolution of cochlea and canals
statocyst, utriculus, sacculus, - 1) cochlea 2) canals
what is frequency/ pitch and units
Hz, number of cycles per second, perceived: tone
what is amplitude/ loudness? units?
dB, Sound pressure, subjective attribute: correlated with physical strength.
human range of hearing in hz and db
20-20,000 Hz
20-120 dB (SPL- sound pressure level)
outer ear functions
CAPTURE sound AND focus sound to the tympanic membrane
MODEST (10Db) amplification of upper range speech frequencies by resonance in the canal
protect inner from external threats
MAIN function of middle ear
mechanical amplification (can provide an additional 20-30dB)
components of the middle ear?
tympanic membrane
ossicles
muscles
oval window
round window
auditory tube
order of the ossicles
malleus, incus, stapes
MAL-I-STA
What is the cochlea (generic)
The hearing part of the inner ear
What are the muscles of the middle ear? (In order from outer to inner)
Tensor tympani muscle- one end attatched to tympanic memb
Stapedius muscle - one end on stapes
What is the function of the cochlea
Transduce vibrations into nervous impulses
What two features of sound does the cochlea successfully transduce into nerve signals?
Frequency and intensity
What structure forms the oval window?
The stapes
What part of the ear is cochlea in?
Inner
If you picture the cochlea as a sandwitch with the stapes on the left (left open- pointy on right)
Which are the 3 compartments of the cochlea?
From top to bottom:
1) scala vestibuli
2) scala media
3) scala tympani
Which chochlear components are bony and which are membranous? What does this mean/ what is the structure of these components?
Top and bottom: scala vestibuli and tympani equivalently are bony and contain perilymph
Scala media: membranous and contains endolymph
What element is the endolymph rich in?
Potassium
What element is the perilymph rich in?
Sodium
What window (oval and round) “attaches” to what scala and what is the direction of the signal?
Oval window to scala vestibuli, signal moves into endolymph and throught the perilymph is transferred to scala tympani to meet the round window
Is the organ of corti a hearing or vestibular organ?
Hearing
Where is the organ of corti located?
ON the basilar membrane of the scala media
What is the name of the membrane of the scala media when it touches the scala vestibuli and when the scala tympani
Vestibular membrane
Vs
Basilar membrane
Which side is base and which is apex of basilar memb and what are its structural features?
Base: near stapes, tight: thick and narrow
Apex: wide (thin) and loose
(miazeime trifti tiriou in pyramid shape with the stapes being the handle and the only addition is that the NARROW part is THICK)
What sits on the basilar membrane?
Hair cells
What frequency sound does the base of basilar memb respond to and what does the apex respond to?
Base Hight freq (think- base is tighter and thicker so only the stronger- pio pola kimatakia- higher freq sound can move this partnof memb
Apex Low freq (less waves, less strength needed to move this side bc its thin)
What are the two types of hair cells in the organ of corti?
Inner hair cells (IHC)
And
Outer hair cells (OHC)
What structure facilitates hair deflection and where does it sit?
Tectorial membrane, sits above hair CELLS (hairs (stereocillia) of hair cells peak through)
What does hair deflection lead to?
Depolarization of the hair cells
What is the role of IHC?
Carry 95% of AFFERENT information OF auditory nerve : meaning transduction of sound into nerve impulses
(Remember bc inner sounds like EAR- sensory- hearing role)
Role of OHC?
Carry 95% of efferent info of auditory nerve : modulation of the SENSITIVITY of the response
What are the hairs on hair cells called?
Stereocillia
In what direction do the stereocilia have to deflect in order for depolarization to happen?
Towards the longest cilium (kinocilium)
What actually happens when the hairs deflect in order to cause depolarization? What happens once the cell is depolarized?
K channels open
Cell depolarises
Release of neurotransmitter to afferent nerve which now also depolarizes
How do higher amplitudes influence rhis depolarization process?
Greater hair deflection
Greater k channel openning
Greater depol
How is the basilar membrane arranged? (Based on what principle/ feature)
tonotopically
Explain the events between k channels oppening and neurotransmitter reaching afferent neeves from hair cell
K channels open
(this is different to typical depolarisation where Na influx is driving the depol)
Depolarization of hari cell
Opening of voltage gated calcium channel
Excitatory neurotransmitter (glutamate ) exocytosed
Neurotransmitter reaches afferent nerve
Where do the nerves sit when near the hair cells?
In PERILYMPH NOT ENDOLYMPH like hair cells
Describe the progression of the auditory pathway
From cochlea to
Brainstem:
1)cochlear nucleus
2)Superior olive
3)Inferior colliculus
To thalamus:
4)Medial geniculate body
Temporal lobe:
5) auditory cortex
What is the name of the ganglions that take info from the cochlea to cochlear nucleus? What nerve do they travel inside?
Spiral ganglions travel inside the vestibulocochlear nerve (8th cranial)
You learned about two different neural pathways. One through auditory nerve and one through vestibulocochlear nerve but they both start with depolarisation of hair cells in cochlea. Make sure you inderstand difference and don’t confuse them.
Both paths involve the transmission of auditory information from the cochlea to higher auditory centers in the brain, but they differ in the specific nuclei and brain regions they involve and in the level of processing that occurs at each stage.
The path via the VESTIBULOCHOCLEAR nerve primarily involves EARLY processing at the BRAINSTEM level,
The path via the AUDITORY NERVE extends to HIGHER cortical areas involved in conscious perception and interpretation of sound.
Specific location of cochlear nuclei in brainstem
Pons
How are the neurons and nuclei in the cochlear nucleus characterised and why?
Monoaural neurons
Ipsilateral cochlear nuclei
Because info up to that point is ipsilateral, after this point IN THE SUPERIOR OLIVE some of the neurons from each ear cross to other side of brain so info is now BILATERAL (means info from both ears in both sides of brain)
Where do some auditory nerves cross in brain
Superior olive and in brainstem
What are the three anatomical types hearing loss? Where is the damage located in each type?
1) conductive: (think- mechanical, blockage problem so:) outer or middle ear
2) sensorineural: cochlear prob or auditory nerve
3) central : brain or brainstem
Two main aspects to consider in hearing loss
Timing and anatomy (location)
Two types of timings in hearing loss
Sudden hearing loss: minutes to days
(Like Acute in other areas of med)
Progressive hearing loss: months to years (like chronic)
What does a normal tympanic memb look like (what is smth characyeristic)
Lustrous look- reflects the light of the osciloscope
Causes of conductive hearing loss in outer ear
Wax
Foreign body (wasps or stuff kids put in ears)
Med name of wax
Cerumen
Middle ear obstruction causes and how can you see
Otitis (bubbles can be seen through the eardrum: indicates liquid in middle ear which is not normal- normal is air)
Osteosclerosis (bone problem)
Inner ear hearing loss causes
Presbycusis (age)
Noise
Ototoxicity (from drugs or chemitherapy or shit)
Nerve damage hearing loss causes
Acoustic neuroma (for ex vestibular schwannoma: tumour made of this tissue) unilateral: usual
Bedside tests advantages and disadvantages
Quick but not that acurate
What are the common bedside tests
1) whisper in ipsilateral ear whilst rubbing fingers in contralateral ear
2)tunic fork tests: 2 weber and rinne test
Describe weber and rinne test
What is an audiogram
Its the graph (loudness over frequency) where they plot your hearing thresholds to define if theres hearing loss.-explains how many decibels you need to hear each frequency
What is a normal hearing threshold
0-20 dB (means that you can hear every frequency at most at 20 dB - the lower dB you can hear a freq at means you have better hearing)
What is the autogram pattern observed in conductive hearing loss ( air conduction and bone conduction trend lines)
Bone conduction normal for all freq
Air conduct relatively lineary abnormal for all freq
What is the autogram pattern observed in sensoryneural hearing loss ( air conduction and bone conduction trend lines)
Air and bone conduction together
Both normal for low freq, get poor for high frequencies
What is a special test done to test normal cochlear functioning? What does this test rely on/ what does it measure?
Otoacoustic emissions (OAEs) test
These are low intensity sounds produced by the outer hair cells as they expand and contract
When do they do otoacoustic emissions test?
Newborn hearing screening and hearing loss monitoring
