Auditory System Flashcards
What bone is the ear found in?
What’s special about it?
The petrous portion of the temporal bone- hardest bone in the body to protect the delicate ear
What is the function of the outer ear?
Capture sound and focus it on the tympanic membrane
Amplify some frequencies via resonance in the canal
Protect the ear from external threats
What is the function of the middle ear?
Amplification by:
a. Focusing vibrations from large surface area to smaller surface area (this increases pressure)
b. using leverage from incus-stapes joint to increase force on to the oval window
What is the function of the inner ear? What structure performs these functions?
The cochlea:
Transduces vibration into nervous impulses
Analyses frequency and intensity of the sound
What are the 3 parts of the cochlea?
Scala vestibuli
Scala tympani
Scala media
What in the cochlea contains perilymph? What are the characteristics of perilymph?
Scala vestibuli and typmani, perilymph is high in sodium
What in the cochlea contains endolymph? What are the characteristics of endolymph?
Scala media, endolymph is high in potassium
Where is the organ of corti located?
In the scala media in the cochlea
What is the basilar membrane?
Where the organ of corti lies
How is the basilar membrane arranged? What does this mean
Arranged tonotopically
It is sensitive to different frequencies at different points along its length
What 2 types of hair cells are found in the organ of corti? How are they arranged?
Inner hair cells arranged in one column
Outer hair cells arranged in 3 columns
How are hairs in the organ of corti deflected?
The tectorial membrane lies above them and allows deflection which then depolarises the cell
Only outer hair cells are in constant contact with the tectorial membrane and assist contact with inner hair cells
What information do the inner hair cells carry and what is their function?
Afferent info
Their function is the transduction of the sound into nerve impulses
What information do the outer hair cells carry and what is their function?
Efferent info
Their function is modulation of the sensitivity of the response.
What hairs of hair cells in the ear called?
Stereocilia
Describe how transduction of sound occours in relation to hair cells?
Stereocilia deflect towards the longest cilium, opening K+ channels
Inflow of K+ depolarises the cell and neurotransmitter is released
Louder sounds causes greater deflection
Describe the auditory pathway
Spiral ganglions from the cochlea project to the ipsilateral cochlear nuclei (in brainstem)
Info crosses at the superior olive
Info then become bilateral:
Travels to inferior colliculus
Then to medial geniculate body (in thalamus)
Then to auditory cortex (in cerebral hemisphere)
What is the human range of hearing for frequency?
20–20,000Hz
What is the human range of hearing for loudness?
0 dB to 120 dB
You can hear more than 120db but this is damaging to the ear
What are the main assessments for hearing?
Audiometry
Tuning fork
Central processing assessments
When are tuning forks used as an assessment for hearing?
To establish absence or presence of hearing
Used to give early and general info when audiometry isn’t available
What is pure tone audiometry?
Measuring hearing acuity for variations in sound intensity and frequency performed using an audiometer
An audiometer froduces sound of varying frequencies and intensities
We can produce an audiogram with plotted hearing thresholds to see if there’s loss of hearing
What is a central processing assessment?
Assessment of hearing abilities other than detection Uses verbal and non verbal tests e.g.: sound localisation filtered speech speech in noise
What is tympanometry?
Examination used to test the condition of the middle ear and mobility of the eardrum (tympanic membrane) and the conduction bones by creating variations in air pressure
What are otoacoustic emissions (OEAs)?
The low intensity sounds a cochlea produces
Produced by outer hair cells
How are OAEs used in newborns?
They are assessed in newborns to screen their hearing ability or measure progression of hearing loss
What type of electrical activity does electrocochleography measure?
From the cochlear and vestibulocochlear nerve
0.2-0.4 ms
What type of electrical activity does auditory brainstem response measure?
From the vestibulocochlear nerve and brainstem nuclei/tracts
1.5-10 ms
What type of electrical activity do late responses measure?
From the primary auditory and association cortex
80-500+ ms
What are the 3 types of hearing loss?
Conductive
Sensorineural
Mixed
Where is the problem located in conductive hearing loss?
Outer or middle ear
Where is the problem located in sensorineural hearing loss?
Inner ear or auditory nerve
Where is the problem located in mixed hearing loss?
Affects more than one part
What about sound is effected in mixed hearing loss?
Conduction and transduction
How can hearing loss be classified?
Mild, moderate, severe or profound
What are some causes of conductive hearing loss?
Wax or foreign body
Otitis (bubbles in eardrum)
Otosclerosis
What are some causes of sensorineural hearing loss?
Presbycusis
Ototoxicity
Nerve VIII tumor
What are the 3 main treatments for hearing loss?
Hearing aids
Cochlear implants
Brainstem implants
What do hearing aids do?
Amplify sound but do not replace any structure
Need to have some preservation of sound
What do cochlear implants do?
Replaces the function of the hair cells by receiving sound, analysing it, transform it into electrical signals and sending an electric impulse directly to the auditory nerve
What do cochlear implants need to work?
A functioning auditory nerve
What do brainstem implants do?
The electrical signals can be sent to a set of electrodes placed directly into the brainstem
When are brainstem implants used?
When auditory nerves are affected
How risky are brainstem implants?
Very risky, should only be used if people have bitemporal auditory nerve damage
What is active amplification?
When a sound is soft, outer hair cells contract and shorten their length to make the tectorial membrane come closer to the hairs. This means a wider area of the tectorial membrane is in contact with the hairs
When the sound is too loud, the outer hair cells increase in length and push the tectorial membrane away
What parts of the cochlear detect what frequencies?
Higher frequency detected in base of cochlear
Lower frequencies in apex of cochlear
How does frequency relate to pitch?
Lower the frequency, lower the pitch
How is hearing affected by age?
Hearing acuity decreases with age, especially higher frequencies
Medium and low frequencies only affected with progression of hearing loss
How can cortical potentials be affected?
Can be affected in neurological problems or processing problems
Why is measuring auditory brainstem responses useful?
Does Not require attention from the patient
Alteration in latency of the waves can tell us location of the deficit
Often used in babies and children
