L35 - auditory pathway Flashcards
role of external ear
receives sound waves
role of auricle
funnels sound waves through internal meatus
middle ear
sound waves –> mechanical waves
inner ear
mechanical waves –> electrical waves
tympanic membrane
eardrum
how are external and middle ear separated
tympanic membrane
external auditory canal
transmits sound waves towards the tympanic membrane
how does middle ear communicate with nasopharynx
auditory tube / Eustachian tube
smallest bones in the body
ossicles
ossicles
malleus
incus
stapes
(MIS)
role of ossicles
vibrate to transmit sound waves
location eustachian tube
connects nasopharynx to middle ear
how does the Eustachian tube change as we get older
as a child it is more vertical
becomes more horizontal as we group
(why children are more prone to ear infections)
functions of eustachian tube
- ventilation
- drainage
- allows for equilibration of pressure between atmospheric and internal environments
why do ears hurt on an aeroplane
- rapid change in pressure
- ears cannot adjust in time
- eustachian tube remains closed
why is the middle ear a high risk space
- connected to nasopharynx (prone to infection)
- connection to mastoid air cells
- inferior jugular vein lies inferior (risk of thrombosis)
- internal carotid artery lies anterior (pulsatile tinnitus)
- traversed by chordates tympani and facial canal (infection risk)
pulsatile tinnitus
can hear a noise which matches the heart rate
- occurs in hypertension sometimes
where is the vestibular system located
inner ear
location of inner ear
petrous part of the temporal bone
vestibular system
- vestibule
- semicircular canals and semicircular ducts
balance and equilibrium
cochlea and cochlear ducts role
hearing
special sense organs in the inner ear
- vestibular system
- cochlear and cochlear ducts
cochlear
snail shaped structure which detects sound frequencies
where can lower sound frequencies be detected
apex of the chochlea
where can higher sound frequencies be detected
nearer the base of the cochlea
fluid filled cavities within the inner ear
- bony outer labyrinth
- membraneous inner labyrinth
bony outer labyrinth
contains perilymph (like extracellular fluid)
membraneous inner labyrinth
contains endolymph (like intracellular fluid)
role of the cochlear duct
separates cochlea into two chambers:
- scala vestibuli (inner)
- scala tympani (outer)
location of perilymph
inside chambers
location of endolymph
inside cochlear duct
helicotrema
the two chambers are continuous at the apex of the cochlea through a narrow slit, the helicotrema
how is sound created
- vibration of stapes creates hydraulic pressure at the apex of the cochlea (helicotrema)
- here, SV and ST meet
- vibrations descent via ST to the round window
- perilymph moves around the bony cochlea, deforming endolymph inside the cochlear duct
- the cochlear duct contains the spiral organ of Corti
- Spiral organ of Corti is stimulated by the deformation of the cochlea duct
- converts fluid pressure into electrical signals
- via the vestibulocochlear nerve (VN8)
location of tectorial membrane
above hair cells
location of basilar membrane
below hair cells
how is the spiral organ of corti stimulated
- cochlear duct deforms
- tectorial membrane moves up and down
- cilia on hair cells detect this
- ion channels open and there is transmission of information
- fluid pressure into electrical signals
auditory pathway
- polysynaptic
- bilateral
1 auditory fibres
- Axons of bipolar neuron in spiral ganglion form the cochlear division of the vestibulocochlear nerve (CNVIII)
- Connect to hair cells
where do primary and secondary auditory fibres synapse
dorsal and ventral cochlear nuclei
cochlear nuclei
- receives afferents from cochlear nerve
- projects bilaterally to superior olivary nucleus
trapezoid body
crossing over midline
what information does the superior olivary nucleus recieves
bilateral auditory information
where does the superior olivary nucleus send information to
ascending fibres to inferior colliculus of the midbrain via the lateral lamniscus bilaterally
auditory part of the thalamus
medial geniculate nucleus
brachium
connects thalamus to inferior colliculus
location of inferior colliculus
tectum of the midbrain
what happens at the inferior colliculus
- receives lateral lemniscus
- may exchange auditory information via the inferior colliculus commissure
- Sends auditory information to MGN via the brachium (arm) of the inferior colliculus
what happens at the medial geniculate nucleus
sends fibres to primary auditory cortex
auditory pathway
- hair cells send neurones to the spiral ganglion
- at spinal ganglion, cochlear part of vestibulocochlear nerve projects to cerebellopontine angle where cochlear nuclei is located
- synapses with second order neurones in dorsal and ventral cochlear nuclei
- projects bilaterally to superior olivary nuclei (crossing over of some neurones)
- synapses and sends ascending fibres to inferior colliculus of the midbrain via the lateral lemniscus
- synapses and neurones travel from IC to MGN via the brachium
- neurones travel from MGN to primary auditory cortex
where does CN8 enter the brainstem
cerebellopontine angle
which part of the primary auditory cortex does low frequency sound project to
anterolateral part (Low = anteroLateral)
which part of the primary auditory cortex does high frequency sound project to
posteromedial part = base
cause of Broca’s aphasia
stroke to anterior branches
cause of Wernicke’s aphasia
stroke to posterior branches
secondary auditory area
specialised for linguistic function
Wernickes area
