Auditory System Flashcards
What three sections is the ear divided into?
Outer, middle and inner ear
Which cranial bone is the ear embedded into?
Petrous portion of temporal bone
What are the 3 functions of the outer ear?
A) To capture sound and to focus it on the tympanic membrane.
B) To amplify some frequencies by resonance in the canal
C) To protect the ear from external threats
What anatomical structures reside within the outer ear?
The pina (auricle) and the external auditory canal (meatus).
What function is performed by ear cilia?
Cilia prevents external elements from entering into the ear
What is the main function of the middle ear?
Amplification of sound
How does the middle ear amplify sound?
Focusing vibrations from the tympanic membrane to a smaller surface area (oval window). The change in surface area means the pressure is increased
Using leverage from the incus-stapes joint to increase the force on the oval window.
What structure connects the outer ear with the middle ear?
The tympanic membrane.
What is the oval window?
The oval window (or fenestra vestibuli) is a membrane-covered opening from the middle ear to the cochlea of the inner ear. Vibrations that contact the tympanic membrane travel through the three ossicles and into the inner ear.
What are the three ossicle bones?
Stapes, incus and malleus
What is the function of the inner ear?
The inner ear is concerned with transducing vibration into nervous impulses, producing a frequency and intensity analysis of the sound.
What structure within the inner ear is associated with hearing?
The cochlea
How many compartments comprise the cochela?
3
What are the three compartments of the cochlea?
Scala vestibuli
Scala tympani
Scala media
Which two cochlea structures contain perilymph?
Scala vestibuli
Scala tympani
Which ion concentration is high within the perilymph?
Sodium
Which ion concentration is high within the endolymph of the scala media?
Potassium
Which hearing organ is located within the scala media?
Organ of Corti
Within which structure does the Organ of Corti reside?
Basilar membrane
How is the basilar membrane arranged?
Arranged tonotopically, using the same principles as a xylophone
-Sensitive to different frequencies at different points along its length.Therefore, cell stimulation occurs at specific frequencies.
At high frequencies, where does the basilar membrane vibrate the most?
At the base.
At low frequencies, where does the basilar membrane vibrate the most?
At the apex, low frequency cells within the apex are participating in the transduction of sound.
Which hair cells comprise the organ of Corti?
Inner hair cells (IHC)
Outer hair cells (OHC)
How are inner hair cells arranged?
Arranged on one column
How are outer hair cells arranged?
Arranged on three columns
Which membrane is in constant contact with the outer hair cells?
The tectorial membrane.
What is the function of inner hair cells?
Transmit 95% of the afferent information of the auditory nerve, their function is the transduction of the sound into nerve impulses.
What is the function of outer hair cells?
Behave as an amplifier, the larger the vibration the more the basilar membrane is displaced (Membrane proteins contract, altering the lengths to allow the tectorial membrane to be brought closer to inner hair cells.)
Transmit 95% of efferents of the auditory nerve, modulation of the sensitivity of the response.
What hairs reside on the surface of hair cells?
Stereocilia
The deflection of the stereocilia towards the longest cilium will cause what?
Mechanical stimulation causes opening of the potassium ion channels.
The ionic interchange depolarises the cell, and the neurotransmitter is liberated onto the afferent nerve.
How is the endolymph adapted to facilitate the depolarisation of the hair cells?
The endolymph consists of an elevated concentration of potassium, thereby upon stimulation, potassium ion influx can proceed, depolarising the cell.
Which nerve is projected from the spinal ganglions of the cochlea to the ipsilateral cochlear nuclei?
Auditory vestibular nerve (VIII)
Information is transmitted from the cochlear nucleus to which structure?
Superior olive
How is information transmitted from the cochlear nucleus to the superior olive?
Bilaterally
Which structure receives efferent transmission from the superior olive?
Inferior colliculus
Which cerebral region is concerned with comprehension of language?
Wernicke’s area
How is hearing organised within the auditory cortices?
Tonotopically.
What is frequency?
The number of wave cycles per second
What is amplitude measured in?
Decibels
What is the human range of hearing?
20-20,000Hz
Loudness: 0db to 120db
What type of scale is the decibel scale?
Log scale
Describe hearing acuity with age?
Hearing acuity decreases with age, particularly higher frequencies.
Medium and low frequencies could be affected with the progression of hearing loss.
What are the hearing assessment procedures for a patient suspected of hearing loss?
- Tunning fork
- Audiometry
- Central processing assessment
- Tympanometry
- Otoacustic Emission
- Electrocochleography
- Evoked potentials
What are the two hearing test assessments conducted with a tunning fork?
Weber test
Rinne test
Which tunning fork test directly stimulates the hair cells?
Rinnes test, since the vibrations travel through the ossicles and internally vibrates the endolymph.
Which assessment tool is used to measure hearing acuity?
Pure tone audiometry (PTA)
What is an audiometer?
Is a device used to produce sound of varying intensity and frequency
What is an audiogram?
Where the hearing thresholds are plotted to define if there is hearing loss or not
A normal hearing threshold is between 0-20db.
What are the three examples of central processing assessment?
Sound localisation
Filtered speech
Speech in noise
What examination is conducted to test the condition of the middle air and the mobility of the tympanic membrane?
Tympanometry
What is tympanic membrane compliance?
How readily sound is conducted through into the middle ear.
What are the four possible causes of a non-compliant tympanic membrane?
Middle ear effusion
Perforation of the tympanic membrane
Eustachian (Pharyngotympanic tube) dysfunction
Occluded ear canal.
What is an otoacoustic emission?
The normal cochlea produces low-intensity sounds called OAEs.
Which cells produce OAEs?
Specifically by the outer hair cells as they expand and contract
What is the purpose of measuring OAEs?
Part of newborn hearing screening and hearing loss monitoring.
An inability to record OAEs is suggestive of dysfunctional outer hair cells.
What is electrocochleography?
0.2-4.0 ms, electrical activity from the cochlea and eighth nerve. Evoked by clicks or tone burst.
what is the auditory brainstem response (ABR)?
1.5-10.0 ms, electrical activity from the eighth nerve and brainstem nuclei and tracts. Evoked by clicks.
What is the late response of an auditory evoked potential?
80-500+ ms, electrical activity from the primary auditory and association cortex. Evoked by tone burst and oddball paradigm.
Which auditory evoked potential is commonly used in clinic?
Auditory evoked potential (ABR)
Alterations in the latency of waves can point to the location of the deficit.
In which patient demography are ABRs used?
Objective measurement in babies and children.
what is a cortical potential?
cortical potential - (neurophysiology) rapid fluctuations of voltage between parts of the cerebral cortex that are detectable with an electroencephalograph. brain wave, brainwave.
what are the three types of hearing loss?
Conductive
Sensorineural
Mixed
What is conductive hearing loss?
Problem is located in the outer or middle ear.
What is sensorineural hearing loss?
Problem is located in the inner ear or the auditory nerve
What is mixed hearing loss?
Both conduction and transduction of sound are affected - more than one region of the air is impacted.
What are the main causes of conductive hearing loss of the outer ear?
Wax
Foreign body
What are the main causes of conductive hearing loss of the middle ear?
Otitis
Otoscerlosis
What is otitis?
Otitis media is inflammation or infection located in the middle ear.
Bubbles can be seen through the ear drum, suggestive there is liquid inside the middle ear.
what is otosclerosis?
Otosclerosis is a condition in which there’s abnormal bone growth inside the ear.
What are the main causes of sensorineural hearing loss?
Prescbycusis- loss of outer hair cells
Ototoxicity
VIII nerve tumour
What function is performed by hearing aids?
Depending on the type, degree and characteristics of the patient there are many options.
Hearing aids amplify the sound, does not replace any structure.
What is the function of a cochlear implant?
The cochlear implant 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 functioning nerve is required to foster function of the cochlear implant?
Auditory nerve
What hearing loss treatment is concerned with affected auditory nerves?
Brainstem implant.
What is a brainstem implant?
When the auditory nerves are the affected structures, the electrical signals can be send to a set of electrodes placed directly into the brainstem.
Which patients are advised to receive a brainstem implant?
Bilateral auditory nerve damage
