Hearing Flashcards
What is exophthalmia?
Eyes bulging out
What are wavelengths/frequency perceived as?
Pitch
What is amplitude perceived as?
Loudness
What is waveform perceived as?
Tone/timbre
What moves the ossicles?
Tympanic membrane
What moves the oval window?
Ossicles
What transforms the physical motion of the oval window into a neural response?
Cochlea
What is the function of the ossicles?
Match impedance of air to impedance of fluid in inner ear
How is the pressure increased at the oval window?
Tympanic membrane 20 times larger
Lever action of ossicles
By how much is the pressure increased at the oval window compared to the tympanic membrane?
200 times
What are the chambers of the cochlea?
Scala vestibuli - superior
Scala media - middle
Scala tympani - inferior
Where is the hearing apparatus located in the cochlear chambers?
Between scala media and scala tympani
What is the basilar membrane?
Coiled part of cochlea
What is the structure of the basilar membrane?
Wider at apex than base
Stiffer at base
Which part of the basilar membrane responds to high frequencies?
Base
Which part of the basilar membrane responds to low frequencies?
Apex
How does the stapes move fluid in the inner ear?
Moves against oval window to move fluid
Which cells are the auditory receptors?
Hair cells
What is the cell type of hair cells?
Specialised epithelial cells
Where are the hair cells located?
Between basilar membrane and reticular lamina
How are the hair cells moved?
Pushed and pulled between basilar membrane and reticular lamina
What is the function of the organ of Corti?
Where sound waves transduced to neural signals
What are the two types of hair cells?
Inner
Outer
Which type of hair cell are there more ov?
Outer
How many stereocilia does each hair cell have?
100
What causes a neuronal signal?
Bending of stereocilia
What is the function of stereocilia of outer hair cells?
Amplify sound
What is the function of stereocilia of inner hair cells?
Transduce sound to electrical signal
What force moves stereocilia?
Shear force
What is the status of potassium channels, and thus membrane potential of hair cells?
K channels partially open
Cell partly depolarisd
What does deflection of the hair bundle towards the tallest stereocilium cause?
Opening of K channels > more K into cell > depolarisation
What does deflection of the hair bundle towards the shortest stereocilium cause?
Closing of K channels > less K into cell > hyperpolarisation
What does depolarisation of hair cells cause?
Opening of voltage-gated Ca channels
What neurotransmitter is released by the depolarisation of hair cells?
Glutamate
Which is larger in hair cells: depolarisation or hyperpolarisation?
Depolarisation
What structure recycles potassium in the cochlea?
Vasa vascularis
Through what structures does potassium cycle in the cochlea?
Scala tympani > scala media > hair cell > scala tympani
What is the proportion of inner hair cell nerves projecting to brainstem nuclei?
95%
How do outer hair cells amplify sound?
Amplify movement of basilar membrane because attached to tectorial membrane
From which structure do outer hair cells receive efferent input?
Superior olivary complex
How do outer hair cells accentuate the movement of the basilar membrane?
Depolarisation > cell contraction
Hyperpolarisation > cell elongation
What is the protein in outer hair cells that changes in size depending on membrane potential?
Prestin
What is the auditory pathway?
Ear - Hair cells - CN VIII - Spiral ganglion Brainstem - Cochlear nucleus in medulla - Superior olive - Lateral lemniscus Midbrain - Inferior colliculus Thalamus - Medial geniculate nucleus Temporal lobe - Auditory cortex
Where does auditory information decussate?
At cochlear nucleus
What mediates sound localisation
Relay nuclei in brainstem
What are the parts of the superior olivary complex?
Lateral superior olive
Medial superior olive
Trapezoid body
What is the function of the superior olivary complex?
Localise sound in horizontal domain
What does the medial superior olive do?
Localise sound by measuring time delay
- Only for low frequencies
What does the lateral superior olive do?
Loalise sound by sensing intensity differences
- Only for high frequencies
How is sound localised in the medial superior olive?
Neurons from both ears synapse on same neuron in medial superior olive
Time delay between two signals measured
How is sound localised in the lateral superior olive?
Head acts like shadow
Ear closer to sound hears a greater intensity than ear on other side > lateral superior olive detects difference in excitation from two ears
Further inhibition of other lateral superior olive via medial nucleus of trapezoid bodies
What is the Brodmann’s area of the auditory cortex?
Area 41
Where is the auditory cortex?
Herschl’s gyrus in temporal lobe
How are neurons organised in the auditory cortex?
By frequency - tonotopically organised
Alternating regions of input from both ears
Core area and belt area around it
To which hemisphere are speech sounds lateralised?
Left
To which hemisphere are environmental sounds lateralised?
Both
To which hemisphere is music lateralised?
Right
What does the dorsal pathway encode?
Where
What does the ventral pathway encode?
What
Where do the dorsal and ventral pathways converge?
Prefrontal cortex
What are some peripheral causes of sudden hearing loss?
Meningitis
Guillain-Barre
Acoustic neuroma
Metastasis
What is a central cause of sudden hearing loss?
MS
What is a cochlear cause of sudden hearing loss?
Infection
- HSV
- Autoimmune disease
- Trauma
- Metabolic
- Vascular
- Ototoxicity
