SM_28b: Ear Function and Testing Flashcards
Lateral portion of external auditory canal is composed of ____, while medial portion of external auditory canal is composed of ____
Lateral portion of external auditory canal is composed of cartilage, while medial portion of external auditory canal is composed of bone
Describe innervation of external auditory canal
Innervation of external auditory canal
- Lesser occipital nerve (C2)
- Auriculotemporal nerve (V3)
- Facial nerve sensory branch
- Greater auricular nerve (C2, C3)
- Auricular branch of vagus nerve
Outer ear functions include ____, ____, and ____
Outer ear functions include amplification / filtering, protection, and localization
- Amplification / filtering: filters sound to external auditory canal, 20 dB amplification, strongest at 4000 Hz
- Localization: interaural time difference, interaural intensity difference (Head Shadow effect)
Tympanic membrane parts include ____ and ____
Tympanic membrane parts include pars tensa and pars flaccida
- Para tensa: how eardrum grows, vibrates ossicles
- Pars flaccida: prevents eardrum from collapsing on itself
Describe the middle ear
Middle ear
- Mucous membrane lining
- Tympanic membrane separates it from external auditory canal
- Eustachian tube connects it to nasopharynx
- Also connected to mastoid air cells
Label the middle ear structures
Middle ear structures
Middle ear muscles include the ____ and ____
Middle ear muscles include the stapedius and tensor tympani
- Stapedius: attaches to stapes, makes ossicles less likely to move, contracts in response to loud sounds / chewing / speaking, facial (CN VII)
- Tensor tympani: helps open Eustachian tube
____ matchmaking occurs in the middle ear
Impedance matchmaking occurs in the middle ear
- Fluid in cochlea has high impedence compared to air in external / middle ear
- Ossicles overcome this with impedance matching and increasing sound pressure
- Multiple mechanisms: area ratio of tympanic membrane to oval window is 20:1, lever action of ossicles
Inner ear is composed of ____ and ____ halves, both of which use ____
Inner ear is composed of vestibular and cochlear halves, both of which use hair cells
- Vestibular: transduces motion and pull of gravity
- Cochlear: transduces sound energy
Scala vestibuli and scala tympani have high ___ and low ___, while the scala media has low ___ and high ___
Scala vestibuli and scala tympani have high Na and low K, while the scala media has low Na and high K
(ionic gradient acts as a battery)
Stapes movement sets up vibration in the ____
Stapes movement sets up vibration in the scala media
- Fluid wave starts at the oval window and scala vestibuli
- Travels from the base to apex of cochlea
- Continues back down through scala tympani to the round window
____ is in the scala media
Organ of Corti is in the scala media
Describe the process of a traveling sound wave
Traveling sound wave
- Fluid wave displaces basilar membrane
- Resonates in specific areas based on frequency
- Appropriate hair cells stimulated: inner hair cells created signal, outer hair cells amplify
Describe cochlear tuning
Cochlear tuning
- Tuning exists through auditory system
- Basilar membrane has varying width and stiffness
- Base of cochlea has stiff basilar membrane so high frequency
- Apex of cochlea has flaccid basilar membrane so low frequency
Base of cochlea has ___ basilar membrane so frequency is ___
Base of cochlea has stiff basilar membrane so frequency is high
Apex of cochlea has ___ basilar membrane so frequency is ___
Apex of cochlea has flaccid basilar membrane so frequency is low
____ are found on inner and outer hair cells
Stereocilia are found on inner and outer hair cells
- Outer hair cells: V or W shaped ranks
- Inner hair cells: straight line ranks
Inner hair cell activation alters ____
Inner hair cell activation alters firing rate
Inner hair cells stimulate ____
Inner hair cells stimulate spiral ganglion cells
- Housed in Rosental’s Canal
- Afferent projections make cochlear nerve
Cochlear nerve stimulates ____
Cochlear nerve stimulates spiral ganglion cells
(normally stimulated by inner hair cells)
Describe the central auditory nervous system pathway
Central auditory nervous system pathway
- Brainstem
- Midbrain
- Thalamus
- Temporal lobe
Cortical auditory processing functions in ____, ____, ____, and ____
Cortical auditory processing functions in pattern recognition, duration discrimination, localization of sounds, and selective attention
Semicircular canals are for ____ movements, while the saccule / utricle are for ____ accelerations
Semicircular canals are for rotational movements, while the saccule / utricle are for linear accelerations
Head rotation causes a fluid shift in the ____, pushing against the ____, causing the hair cells to ____
Head rotation causes a fluid shift in the semicircular canal, pushing against the cupula, causing the hair cells to depolarize
Describe ear testing
Ear testing
Conductive hearing loss is ___
Conductive hearing loss is when sound is blocked on its way to the cochlea
Sensorineural hearing loss is ____
Sensorineural hearing loss is when the cochlea and/or auditory nerve are not working
Air conduction is ____
Air conduction is the normal auditory pathway
Bone conduction is ____
Bone conduction is when vibrations on bone directly transmit to cochlea
Describe the Weber test
Weber test
- Vibrating tuning fork is placed on middle of the forehead or vertex
- Normal hearing: Equal sound in both ears
- Sensorineural hearing loss: sound lateralizes towards the good ear (away from bad ear)
- Conductive hearing loss: sound lateralizes towards bad ear
Sensorineural hearing loss on the Weber test is when ____
Sensorineural hearing loss on the Weber test is when sound lateralizes towards the good ear (away from bad)
Conductive hearing loss on the Weber test is when ____
Conductive hearing loss on the Weber test is when sound lateralizes toward the bad ear
Describe the Rhinne test
Rhinne test
- Vibrating tuning fork placed on mastoid bone (bone conduction) and moved to outside of ear (air conduction) when patient can no longer hear sound
- Normal hearing: air conduction is louder than bone (+ Rhinne)
- Sensorineural hearing loss: air conduction is louder than bone (unless “dead ear”)
- Conductive hearing loss: bone conduction is louder than air (- Rhinne)
Sensorineural hearing loss on Rhinne test is when ____
Sensorineural hearing loss on Rhinne test is when air conduction is louder than bone (unless “dead ear”)
Conductive hearing loss on Rhinne test is when ____
Conductive hearing loss on Rhinne test is when bone conduction is louder than air (- Rhinne)
Describe conventional audiometry (audiogram)
Conventional audiometry (audiogram)
- Pure tones at different frequencies, using air and bone conduction
- Increasing sound levels (dB) with worsening hearing loss
- Higher on chart is better: lower on chart (higher dB) is worse hearing
Describe profound hearing loss
Profound hearing loss
- Poor word understanding
- Distortion
- No role for hearing aids
- Cochlear implants
Tympanometry is used to ___ and ___
Tympanometry is used to check pressure in ear and help establish Eustachian tube function
(pressures should be the same on either side of eardrum)
Describe speech testing
Speech testing
- Speech reception thresholds: when sound is recognized as speech
- Word recognition scores: ability to understand what is being spoken: closed set (4 options), open set (all words)
Describe acoustic reflex testing
Acoustic reflex testing
- Response of stapedius muscle to loud sound
- Reflex arc through auditory (VIII), brainstem, and facial (VII) bilaterally
- Tone presented to each ear and response measured in both
- Absent in severe hearing loss / stapes fixation
Otoacoustic emissions are ____
Otoacoustic emissions are sounds given off by the inner ear when the cochlea is stimulated by sound
- Vibration produces a nearly inaudible sound that echoes back into the middle ear
- Sound can be measured with a small probe inserted into ear canal
- When click sound is applied to ear, it clicks back
- Absence of otoacoustic emissions: block in air conduction or within cochlea
- May be present with deficits of auditory nerve (VIII)
Describe audiograms in children by age
Audiograms in children by age
- Age 0-5 months: behavioral observation audiometry - eye widening, startle, quieting
- Age 6 months - 2 years: visual reinforcement audiometry - toy lights up if they turn towards sound
- Age 2-5 years: conditioned play audiometry - listening game (putting toys in a bucket)
Auditory brainstem response is ___
Auditory brainstem response is evoked potential generated by brief click
- Amplitude is averaged and charted against time
- Done in young or developmentally delayed children or those with severe / profound hearing loss during cochlear implant workup
