Auditory pathway Flashcards
What is found in the petrous part of the temporal bone? (2)
- cochlear
2. internal acoustic meatus
What type of energy does the external ear transmit?
sound waves
What type of energy change occurs in the middle ear? (2)
Sound waves to mechanical
What type of energy change occurs in the inner ear? (2)
mechanical to electrical
What cranial nerves run through the internal acoustic meatus?
vesitbulocochlear nerve (CN VIII)
facial nerve (CN VII)
What is the petrous part of the temporal bone like?
very hard
What is the ear drum known as?
tympanic membrane
What does the auditory tube do?
Connects to nasopharynx
enables air passage to maintain equilibrium of pressure
- goes wrong in planes
Why is the middle ear a high risk space? (5)
- connected to nasopharynx - prone to infection
- connected to mastoid air cells - infection may spread to middle cranial fossa
- internal jugular vein lies inferior - thrombosis risk
- internal carotid artery lies anterior - link to pulsatile tinnitus
- traversed by chord tympani and facial canal - infection risk
What also increases infection risk especially concerning nerves?
holes which nerves pass through
What is the inner ear?
series of fluid filled cavities
In the inner ear, what are the names of the series of cavities the petrous part of the temporal bone have and what do they contain?
- vestibule
- SSC - superior semicircular canal
- cochlea
perilymph
Where does the cochlear duct run through and what type of lymph does it contain?
runs through the cochlea
contains endolymph
What is the cochlear duct?
a membranous sac (closed tube) contain endolymph
What is the ion conc like in endolymph?
low sodium
high potassium
Things you need to know in inner ear? (5)
- posterior semicircular canal and duct
- vestibule
- lateral semi-circular canal and duct
- anterior semicircular canal and duct
- cochlea
What type of lymph does the cochlea contain?
perilymph
What two chambers does the cochlear duct separate the cochlea into?
- scala vestibuli
2. scala tympani
What are the two chambers scala vestibuli and tympani continuous of?
apex of cochlea - helicotrema
How is sound transmitted in the cochlea?
- hydraulic pressure is created in the perilymph
- this pressure is created by vibrations of Stapes and pass to apex via the Scala vestibuli
- the vibrations pass through the helicotrema and descends via the Scala tympani to the round window
- as fluid moves around the cochlea it deforms the fluid, endolymph in the cochlear duct
What makes up the roof and floor of the cochlear duct?
roof - vestibular membrane
floor - basement membrane
What is the auditory receptor?
The spiral organ (of Corti) on the basilar membrane
What does the spiral organ contain?
hair cells with the tips embedded into the tectorial membrane
What is the spiral organ stimulated by?
the deformation of the cochlear duct by perilymph in the surrounding Scala vestibuli and scala tympani
What components do you need to know of the cochlear duct and the things that surround the cochlear duct?
- vestibular emmbrane
- tectorial membrane
- cochlear nerve
- spiral ganglion
- scala tympani
- basilar membrane
- spiral organ
- cochlear duct
- scala vestibuli
What are primary auditory fibres?
axons of bipolar neurone in spiral ganglion
What do the primary auditory fibres form?
the cochlear nerve which becomes part of the vestibulocochlear nerve - CNVIII
Where does the primary auditory fibres enter?
brainstem at cerebellopontine angle
Where does the primary auditory fibres synapse with secondary neurons?
in ventral and dorsal cochlear nuclei
What are the auditory centres in the brain stem?
- medial geniculate nucleus of the thalamus
- inferior collicus
- superior olivary nucleus
- cochlear nuceli
Is the auditory pathway polysynaptic?
yes
Why is the auditory pathway bilateral?
so sound can be localised as it compares 2 inputs
What 2 inputs does the bilateral auditory pathway compare?
- timing
2. loudness
How does the basillar membrane respond to sound?
different regions of the basillar membrane respond maximally to sounds of a different pitch
What frequency of sound does the apex of the basilar membrane respond to?
low pitch
Where does sound information of low pitch project to?
anterolateral part of Heschl’s gyrus
What hemisphere houses the 2ndary auditory area?
left
What does the 2ndary auditory area entail? (which areas)
- Brocas - anterior and motor production of words
2. wernickes - posterior and sensory and understanding
What is aphasia a result of?
results of f=damage to speech areas - broca’s (non-fluent) or Wernickes (fluent)
What supplies wernicke’s and broca’s?
middle cerebral artery
Would a unilateral lesion have any effect on hearing?
no as the auditory pathway is bilateral however ability to localise sound may be impaired
What must be affected in a person who is deaf (usually in both ears)?
the peripheral part of the auditory (up to the brain stem) must be affected
What is conductive deafness?
defect of sound transmission up to spiral ganglion
What is sensorineural deafness?
defect in function of spiral ganglion or cochlear nerve
What combination of deafness could you get?
conductive and sensorineural
