1b Auditory Systems Flashcards
What does a vestibular organ capture?
Captures low frequency motion (movements)
What does a hearing organ capture?
Captures high frequency motion (sound)
What is meant by the frequency of a sound?
The number of cycles of the sound per second, perceived tone
What is the frequency measured in?
Hertz
What is the amplitude?
the sound pressure - therefore corresponding to loudness
What is the human range of hearing?
20-20000 Hz
0-120 decibels
What are the functions of the outer ear?
Capture sound and focus it onto the tympanic membrane
Modest amplification of the upper range of speech frequencies by resonance in the canal
To protect the ear from external threats
By how much does the outer ear amplify the sound?
10 DB
What is the middle ear?
All the structures from the tympanic membrane to the oval window
What is the main function of the middle ear?
Mechanical amplification (Provides an additional 20-30DB)
What happens to the tympanic membrane when a sound hits it?
It vibrates at the same frequency as the sound wave which just hit it
What are the ossicles?
The three smallest bones in the body -
Malleus
Incus
Stapes
What is the inner ear called?
Cochlea
What is the function of the cochlea?
function is to transduce vibration into nervous impulses
What two things does the cochlea capture?
Captures the pitch and intensity of the sound
Where does the stapes connect to the cochlea?
The oval window
Where does the sound go from the oval window of the cochlea?
Scala Vestibuli
What does the scala vestibuli and the scala tympani contain?
Perilymph
What does the scala media contain?
Endolymph
What is the perilymph high in?
Sodium
What is the endolymph high in?
Potassium
Where is the hearing organ or Organ of Corti Located?
In the basilar membrane - separates the scala media and the scala tympani
What type of structures are the scala vestibuli and the scala tymphani?
Bone structures
What type of structure is the scala media?
Membranous Structure
What structure does the Organ of Corti lie in?
The basilar Membrane
Which sound frequency moves the base of the basilar membrane?
high frequency sounds
Which sound frequency moves the apex of the basilar membrane of the cochlea?
Apex - Wide and loose
Moved by lower frequency (Hz) sounds
How is the basilar membrane arranged?
Tonotopically
What are the two types of hair cells which the organ of corti contains?
Inner hair cells
Outer hair cells
What is the difference in the way the inner and outer hair cells of the organ of corti are arranged?
Inner = one line
Outer = three lines
What sits above the hair cells in the cochlea?
the tectoral membrane
What does the tectoral membrane allow?
Allows hair deflection, which in turn depolarises the cell
Inner hair cells carry which type of signal?
Afferent signals
Which nerve do the inner hair cells pass information to?
Auditory nerve
What is the function of the inner hair cells?
Transduction of the sound into nerve impulses
What do the outer hair cells do?
Carry efferents from the auditory nerve
What is the function of the Outer Hair cells?
Modulate the sensitivity of the response
What are the hairs of the hair cells called?
Stereocilium
What is the longest cilium called?
Kinocilium
What does deflection of the stereocilium towards the longest cilium cause?
Opening of K+ Channels
What happens inside the hair cell when the stereocilium are deflected towards the tallest one?
K+ Channels open, Causes depolarisation
Opens Ca2+ channels
leads to the release of an excitatory neurotransmitter (Glutamate) and therefore the simulation of the afferent nerve
How does louder sounds affect the sterocilium?
Louder sounds deflect the kinocilium more
What causes the movement of the sterocilium?
The sheer force of the tectoral membrane over the top of the sterocilium will move them
What happens when the cells are hyper-polarised?
K+ channels are closed
What happens to the nerves from the spiral ganglion?
Via the vesticulo-cochlear nerve, they travel to the ipsilateral cochlear nuclei in the pons
Which cranial nuclei come into the pons?
5,6,7,8
Where is the cochlear nuclei?
In the pons
Where does the auditory system nerve decussate?
In the brain stem - in the pons, at the superior olive level
AWhat area of the thalamus is related to hearing?
Medial geniculate body
Where is the auditory cortex>
The temporal lobe
After what point are the auditory connections bilateral?
After the superior olive level
What are the three types of hearing loss?
Conductive
Sensorineural
Central
What is conductive hearing loss?
Problem is located in the outer / middle ear
What is sensorineural hearing loss?
Damage to the sensory organ (cochlear) or the nerve (auditory nerve)
What is central hearing loss?
originates in he brain and the brainstem
What is the time fram for sudden hearing loss?
Minutes to days
What is the time frame for progressive hearing loss?
Months to years
What is cerumen impaction?
Wax in the ear
What is otisis
inflammation of the middle ear- bubbles can be seen through the ear drum, suggesting there is liquid inside
What is otosclerosis?
When you get breakdown of the middle ear bones
What are the causes of sensorineural hearing loss?
Inner ear - noise, presbycusis, ototoxicity
Nerve - acoustic neuroma
What is presbycusis?
Deterioration of the hair cells due to old age
What is ototoxicity?
Chemotherapy causes inner ear nerve damage
And Antibiotics - Gentomycin = aminoglycosides
What is a vestibular schwaanoma?
A unilateral tumour which causes damage to the nerve resulting in sensorineural hearing loss
What does a tuning fork?
two tests assess the presence of gross hearing
what are the two tests done with a tuning fork called?
Weber test
Rinne test
What is the webber test?
Tuning fork placed on top of the head - sound should be heard in the middle
What is the Rinne test?
tuning fork placed behind the ear
If Rinne test is louder than webber, what does this suggest?
That your problem is an outer ear / conductive problem
What pattern on a audiogram would be seen in conductive hearing loss?
Difference between Bone and air conduction
What pattern on a audiogram would be seen in sensorineural hearing loss?
Same conduction between air and bone
What are the four treatments of hearing loss?
Fix underlying cause
hearing Aids
Cochlear Implants
Brainstem Implants
What is Otoacoustic emissions?
They are the normal sounds produced by the cochlea
produced specifially by the outer hair cells as they expand and contract
What special test is part of the newborn hearing screening and hearing loss monitoring?
Otoacoustic Emissions
