Week 11: Auditory Pathway Flashcards
Which bone does the ear sit around?
Temporal bone
How is the ear divided?
External ear:
receives sound waves
Middle ear:
sound waves –> mechanical waves through tympanic membrane
Inner ear:
Mechanical waves –> electrical waves
What is the function of the auricle?
to funnel sound waves into the external acoustic meatus
What structure separates the external ear from the middle ear?
tympanic membrane
What structure connects the middle ear to the nasopharynx?
via the Eustachian tube (a.k.a auditory tube)
The middle ear contains 3 ossicles. What are they called?
- Malleus
- Incus
- Stapes
What happens to the eustachian tube as we age?
it becomes more vertical (it is more horizontal in infants - this is why they are more prone to ear infections as it is easier for infection to travel)
What are the functions of the eustachian tube?
- ventilation
- drainage
- equilibriate the pressure between the external and internal environment
What are the 3 techniques to open the Eustachian tube to equilibriate pressure again?
yawn
swallow
pinch nose and blow out of cheeks
Why is the middle ear a high risk space?
- Connected to nasopharynx –> prone to infection
- Connected to mastoid air cells –> infection can spread to middle cranial fossa
- Internal jugular vein lies inferior –> risk of thrombosis
- Internal carotid artery lies anterior
- Transversed by chorda tympani and facial canal –> infection risk
What is pulsatile tinnitus?
ringing that matches your heart rate
The inner ear is composed of 2 special sense organs. What are they?
- Vestibular system
- vestibule, semi circular canals, semi circular ducts
- important for balance - Cochlear
- cochlear ducts
- important for hearing
In the cochlear, which part detects:
- Low frequency sound
- High frequency sound
- Apex of cochlea
2. Base of cochlear
What are the 2 fluid filled cavities found in the cochlea?
- Bony labyrinth (outside)
2. Membranous labyrinth (inside)
What fluid does the bony (outer) labyrinth contain?
perilymph
What fluid does the membranous (inner) labyrinth contain?
endolymph
The cochlear duct seperates the cochlea into two chambers. What are they called and what fluid are they filled with?
- Scala vestibuli
- Scala tympani
both filled with perilymph
How are the scala vestibuli and scala tympani continous with the apex of the cochlea?
through a narrow slit called the helicotrema
What is inside the SV and ST chamber?
the cochlear duct which contains endolymph
Where is the spiral organ (of Corti) ?
- inside the cochlear duct
- sits above the basilar membrane
- contains hair cells with tips embedded into the tectorial membrane
How does the spiral organ of corti detect and transmit sound?
- upon movement of the cochlear duct by the perilymph in the surrounding SV and ST, the tectorial membrane moves up and down
- the cilia detect this movement and transmit information to cochlear nerve fibres
- converts fluid pressure into electrical signals via cochlear nerves
Explain how sound waves from air is transformed into electrical information (6 steps)
- External ear funnels sound waves via the middle ear
- Ossicles vibrate - malleus, incus and stapes
- Stapes is in contact with oval window
- This vibration is transmitted into fluid of the scala vestibuli then scala tympani
- Whilst the fluid moves, we have movement vibration of the tectorial membrane inside the spiral organ of corti
- This movement is detected by hair cells, which transmit through axons that transmit information via the cochlear division of the vestibulocochlear nerve
What fluid does the cochlea contain
perilymph
Which structures do vibrations travel through between the stapes and the round window?
In order: Stapes Perilymph SV Helicotrema ST Round window
Give 4 features of the auditory pathway?
- polysynaptic
- tonotopically organised
- bilateral (so sound can be localised)
- it compares two inputs - timing and loudness
Explain the 7 steps in the auditory pathway
- Vestibulocochlear nerve reaches the brainstem at the cerebellopontine angle
- At this level, there are synapses with cochlear nuclei
- We then have 2nd order neurones travelling up to higher levels in the brainstem
- Further synapses at the superior olivary nucleus
- Axons carry information up to the inferior colliculus
- Neurones project to the medial geniculate nucleus of the thalamus
- Neurones project to the auditory cortex
Where do 1st order neurones emerge from and connect to?
1st order neurones emerge from the spinal organ of corti and connect to the hair cells
Where are dorsal and ventral cochlear nuclei found?
just lateral to the inferior cerebellar peduncle
What is the cochlea nuclei role in the auditory pathway?
- receive afferents from cochlear nerve
- project bilaterally to superior olivary nucleus
What is the role of the superior olivary nucleus in the auditory pathway?
- SON receives bilateral auditory information
- sends ascending fibres to inferior colliculus via lateral lemniscus bilaterally
Where is the inferior colliculus?
in the tectum of the idbrain
What is the role of the inferior colliculus in the auditory pathway?
sends auditory information to the MGN via the brachium (arm) of the inferior colliculus
What is the role of the MGN in the auditory pathway?
Sends fibres to primary auditory cortex via acoustic radiations
What does the brachium of the inferior colliculus do?
connects the inferior colliculus to the medial geniculate nucleus
Which region of the basilar membrane responds to:
- Low frequency
- High frequency
- AnteroLateral part
2. Posteromedial part
Which two areas are specialised for linguistic function?
- Broca’s area
- responsible for motor, production of words - Wernicke’s area
- responsible for sensory, understanding of words and fluency
What and where is heschl’s gyrus?
=primary auditory cortex
in superior temporal lobe
Explain the auditory reflex involing the stapedius muscle
- when auditory information reaches the superior olivary nucleus, fibres travel to the stapedius and tensor tympani muscle
- interneurones meet nuclei of CN VII (which innervates stapedius) or nuclei of CN V3 (which innervates tensor tympani)
- to prevent damage during loud noises
Explain the auditory reflex that occurs at the level of the inferior colliculus?
via interneurones, the auditory information can reach nuclei of CN III, IV and VI which innervates eye movements and spinal nerves that move our neck, body and trunk in response to sound
