Mechanisms and Pathologies of Hearing Flashcards Preview

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Flashcards in Mechanisms and Pathologies of Hearing Deck (44):

What can cause a conductive hearing loss?

Otitis media or glue ear
Blockage in external auditory meatus
Ruptured tympanic membrane
Eustachian tube dysfunction


What is a sensorineural hearing loss?

When there is damage to the cochlea, cochlear nerve or the central auditory pathway


What can cause sensorineural hearing loss?

Damage to hair cells via ototoxic drugs or excessive noise
Spiral ganglion damage such as acoustic neuroma
Auditory neuropathy


What is otosclerosis?

A bony outgrowth of the stapes which impedes movement against the oval window


How does otitis media cause a conductive hearing loss?

Fluid accumulation and pressure changes in the middle ear, impeding auditory ossicles


Which is rinne's test?

When you place the tuning fork on the mastoid process then by the ear


Which test is weber's test?

When you place the tuning fork on the forehead


Rinne's test: bone > air right ear
Weber's: lateralises to right ear

What is the diagnosis?

Conductive hearing loss in right ear


Rinne's: bone > air (left ear)
Weber's: lateralises to right ear

What is the diagnosis?

Sensorineural deafness in left ear


Rinne's: air > bone both ears
Weber's: lateralises to left ear

What is the diagnosis?

Sensorineural hearing loss in right ear


If Weber's lateralises to the left ear, what are the two possible diagnoses?

Conductive hearing loss in left ear
Sensorineural hearing loss in right ear


If bone is louder than air in a Rinne's in the left ear, what are the two possible diagnoses?

Conductive hearing loss in left ear

Complete sensorineural deafness in left ear (because sound is conducted by bone to the other ear)


What is conductive hearing loss?

Where there is a problem with the transmission of sound from the outer to the inner ear


What is sound?

A compressed airwave, travels at 343 m/s


What is frequency measured in?

Cycles per second (Hz)


What is magnitude measures as?

Intensity of the sound in decibels


What attaches the stapes to the oval window?

The annular ligament


What does the middle ear do?

Allows conversion of sound waves in the air to the fluid of the inner ear


How is the pressure transmitted to the oval window amplified?

Because the area of the tympanic membrane is greater than that of the oval window
Mechanical efficiency of the ossicles acting as levers


What does the inner ear consist of?

The bony labyrinth
The membranous labyrinth
The organ of Conti


In which bone is the bony labyrinth found?

The petrous part of the temporal bone


Which parts does the bony labyrinth of the inner ear make up?

The vestibule
Three semicircular canals


Which part of the inner ear is responsible for hearing in response to vibrations?

The cochlea


What do the cavities of the bony labyrinth contain?



What is the cochlear canal divided into?

Scala vestibule
Scala tympani


Where do the vibrations travel in the inner ear?

Oval window - scala vestibule - out via the round window


What lies within the cochlea which is part of the membranous labyrinth?

The scala media/cochlear duct


What is the cochlear duct filled with and what is it bound by?

Endolymph - high conc of K+ and low conc of Na+

Vestibular/Reissner's membrane and the basilar membrane


Where is the organ of Conti?

On the basilar membrane of the cochlear duct


Function of the inner hair cells?

Sense sound - move in response to endolymph


Function of the outer hair cells?

Amplify sound


Where are the inner and outer hair cells found?

Both in the organ of Conti

Outer hair cells are embedded in the tectorial membrane which runs the length of the organ of Conti


Where do signals produced by the hair cells travel?

To the spiral/cochlear ganglion which are bipolar neurones, forming at the base of the hair cell
Theses nerve endings form the cochlear division of CN VIII


How do hair cells move?

Compression of perilymph in scala vestibule and tympani, producing oscillatory movements in the basilar membrane

Movement of the membrane causes movement in tips of stereocilia
-inner hair cells relative to endolymph
-outer hair cells relative to tectorial membrane


How does movement of the stereocilia generate a signal?

Mechanical displacement causes influx of K+ through their membrane
This depolarises the hair cell
Causes influx of Ca2+ through VGCC
Intracellular rise in [Ca] causing release of neurotransmitter in the spiral ganglion cells
The action potential then propagates along the nerve fibres of the CN VIII


What is the tonotopic distribution of responding receptors?

Hair cells located at the base of the basilar membrane respond to hi frequencies
Those at the apical aspect of the membrane respond to low frequencies


Where does the central auditory pathway begin?

With bipolar neurones in the vestibulocochlear nerve


Where does the vestibulocochlear nerve travel?

Through the internal acoustic meatus, into the posterior cranial fossa where it divides into the vestibular and cochlear divisions at the level of the brainstem to rostral medulla


Where do bipolar neurones synapse onto second order neurones?

In the cochlear nuclei of the medulla
Then project in a tonotopic manner


Where do the second order neurones travel?

Some synapse in the ipsilateral or contralateral superior olivary complex

Others pass contralaterally and synapse directly in the inferior colliculus


What does the superior olivary nucleus allow?

Localisation of sound in acoustic space
-discriminate differences in time of arrival or intensity of sound to each ear


What do neurones passing from the superior olivary nucleus to the inferior colliculus pass through?

The lateral lemniscus


Where do axons go from the inferior colliculus?

Medial geniculate nucleus
Then projected to the auditory cortex (Broadman's area in the temporal lobe)


Summary of the central auditory pathway?

Spiral ganglion cells
Cochlear nucleus
Superior olivary complex
Inferior folliculus
Medial geniculate nucleus
Auditory complex