Hearing Flashcards
Sound properties - pitch/frequency
Measured in Hertz (Hz)
Sound properties - loudness
Amplitude; size of the waves
What frequency range can humans normally hear?
20-20,000 Hz
What frequency range is human speech?
250-8000 Hz
Hearing changes with age
Frequency range that can be heard decreases with age
High frequency sounds lost first
Sound wave properties
Condensation (peak)
Rarefaction (trough)
3 broad ear parts
External
Middle
***
Parts of the external ear - Pinna/Auricle
Parts of the external ear - Tympanic membrane/ear drum
Parts of the middle ear - ***those three tiny bones
Tiny join capsules *
Parts of the middle ear - Eustachian tube
Auditory tube
“Ears popping” -> equalising pressure
Parts of the middle ear - mastoid air cells
Involved I keeping pressure
Parts of the inner ear - fluid
Perilymph
Parts of the inner ear - cochlear
Most common cause of hearing loss presentation at the GP
Over-presence of wax
Function of middle ear (broad)
Amplification of sound
Function of inner ear (broad)
Conversion of vibrations into electric signals
Middle ear - impedance matching
Greater area of tympanic membrane than oval window
Level action of teh major ossicles
Buckling of the tympanic membrane
Acoustic impedance
Ratio of pressure to velocity - high impedance means that you need to apply a high pressure to a structure in order to move it
***
Impedance mismatch
Impedance matching mechanisms
Area ratio
Lever ratio
Area ration
tympanic membrane is larger in this area than in the stapes footplate, like a drawing pin increasing pressure at the sharp end
Lever ratio
processes of the malleus and incus are unequal in length. This increases the force (but decreases the velocity) at the stapes, just as it is easier to let a load in a wheelbarrow when the load is closer to the wheel than the handles are
Names of the three bones in the middle ear
Malleus (hammer)
Incus (anvil)
Stapes (stirrup)
Transmission fo vibrations by bones in the middle ear
Malleus attached to tympanic membrane
Vibration of the membrane & thus the malleus
Malleus attached to incus
Incus attached to stapes
Foot of stapes fits into the oval window
Modification & protection
2 skeletal muscles attach to the ossicles
They reflexively dampen excessive loud sounds
Sound attenuation reflex (works for loud sounds not for high frequency)
Sound attenuation reflex
Responds effectively to low frequency sounds
Will decrease up to 100 fold the energy that reached the eardrum
It’s a slow reflex (useless against gunshots; only lasts ~10 minutes)
*** for making notes -> Paget’s disease as a case study
*** for making notes -> secretory otis media as a case study
Broad roles of the inner ear
Hearing
Balance
Inner ear broad structure notes
Interconnecting fluid filled tunnels and chambers within the petrous portion of the temporal bone
Inner ear - boney labyrinth
Cochlea - hearing
Vestibule - balance
Semicircular canals - balance
Cells in the cochlea
Highly modified
Forming the spiral organ (organ of corti)
Epithelial cells + specialised sensory hair cells
Cochlea
Specialised sensory hair cells
No axons
Basilar regions covered with synaptic terminals of sensory neurons
Embedded in the tectoral membrane
Organ of corti
12,000 outer hair cells in 3 rows
3,500 inner hair cells in a single row; form synapses with afferent nerve terminals -> axons -> cochlear clues of the brainstem
Hair celll - steocilium
Sterocilium look kinda ike villi & are connected by tip links
***
Tip Links
Tiny links between stereocilia
The bending action of tip links (caused by sound vibrations I think**) causes mechanical transduction
Genetic causes of deafness CAN be linked to
Stereocilia & involved proteins
Transduction
Displacement of hair cells causes high potassium and low sodium levels in cells
Process of transduction
Stereocilia bent
Receptor potential varies with oscillation of sound stimuli
Overall net depolarisation
Electrical potential of the perilymph
Signal is called the cochlear microphonic
No latency, no threshold
How is the cochlear organised?
Tonotopically -> High frequency at start and low frequency at end
Tuned hairs
Each inner hair cell responds to specific frequency band
Each afferent axon connects to only one hair cell
Each hair cell thus displays sharp defined tuning curve
Each hair cell has a low threshold to simulation at its characteristic frequency
Auditory pathways
Travelling from the cochlear to the auditory nerve, the there are 2 pathways: up the dorsal cochlear nucleus or the **
Either way arrives at the **
Conductive deafness
Anything that blocks out ear or middle ear
Sensorineural deafness
Cochlear -> noise trauma, drugs, infection, congenital presbycusis
Auditory nerve -> tumour (acoustic neuroma, very rare)
Tinnitus
Common complaint
Associated with a number of conditions
Can be accompanied by vertigo and/or partial deafness
Tests for deafness
Weber’s test
Rinne’s test
Weber’s test
Bone conduction
Tuning fork in the middle of the skull
Rine’s test
Air conduction
Tuning fork on mastoid process, when no longer heard then use sound conduction
