NS 8: Special sense of hearing and ANS Flashcards

1
Q

Lobe of cerebral cortex associated with hearing?

A

temporal

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2
Q

common causes of conductive deafness?

A
otitis externa
otitis media
otosclerosis
excess cerumen in external ear
glue ear- chronic otitis media with effusion
ruptured tympanic membrane
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3
Q

What component of the ear may be damaged with ageing, causing sensorineural deafness?

A

hair cells= vibration sensitive cells found in the Organ of Corti

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4
Q

when are tuning fork tests reliable?

A

when a single type of hearing loss in 1 ear only

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5
Q

what are the 2 sound parameters detected by the cochlea?

A

frequency and volume

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6
Q

different functions of inner and outer hair cells in organ of corti?

A
inner= 1 row which detect sound
outer= 3 rows which amplify sound
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7
Q

causes of sensorineural hearing loss?

A

sensory: hair cell destruction e.g. noise related
hair cell death e.g. with aminoglycoside drugs
neural: -Spiral ganglion damage (e.g. acoustic neuroma)
– Age-related hearing loss (ARHL, possible links with dementia?)
– Tinnitus - ‘phantom’ sound (associated with hearing loss)
– Auditory Neuropathy (ass. with hyperbilirubinaemia, neonatal Jaundice)
– Monaural deafness - destroys ability to localise a sound.

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8
Q

examples of 4 treatments for hearing loss?

A

hearing aid
cochlear implant
hair cell regeneration
cochlea nucleus implants

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9
Q

what structure does the organ of corti lie on?

A

the basilar membrane= width of which increases with distance from stapedial end, (from base to apex) and coupled to decrease in stiffness, this means high frequency sounds maximally displace membrane at stapedial end and low-frequency sounds maximally activate apical end.
=tonotopic localisation.

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10
Q

which cells provide most of the signal in the vestibulocochlear nerve?

A

inner hair cells- receive little input from brainstem in contrast to outer hair cells- receive input from superior olivary complex which modifies the shape and response properties of these cells. Some also make direct contact with tectorial membrane which inner hair cells don’t, which may be important in modifying inner hair cells response to sound.
inner and outer hair cells change shape along scala media, modifying their tuning characteristics.

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11
Q

test used to measure mobility of tympanic membrane?

A

tympanometry

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12
Q

anatomical layers and neural innervation of tympanic membrane?

A

outer layer= skin= stratified squamous keratinized epithelium
middle layer= fibrous CT
inner layer= low columnar respiratory epithelium

neural innervation: outer part= auriculotemporal nerve from mandibular division of trigeminal, and small branch of vagus (auricular branch)
inner part= glossopharyngeal nerve * so infections of oropharynx may produce earache as same neural supply- referred pain.

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13
Q

MAIN function of auditory ossicles?

A

impedence matching: without them, most of sound energy would be reflected as it hits the high impedence cochlear fluid, so sound would be lost.
also amplify force of tympanic membrane, and so sound is amplified and concentrated to oval window.

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14
Q

joints between ossicles?

A

synovial joints

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15
Q

functions of tensor tympani and stapedius?

A

prevent excessive vibrations of ossicles so offer protection to ear from large noises.

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16
Q

surfaces of middle ear?

A

anterior wall= carotid wall-ICA
posterior wall= mastoid wall- mastoid air cells
medial wall= outer plate of oval window
lateral wall= inner plate of tympanic membrane= low resp. columnar epithelium
roof= tegmen tympanum
floor= jugular wall- IJV runs underneath

17
Q

4 functions of eustachian tube?

A

ventilation of middle ear
equilibration of air pressure between middle ear and atmosphere
drainage of mucous secretions from middle ear into nasopharynx
prevent infections of middle ear from upper respiratory tract by lymphoid tissue (adenoids) close to opening of Eustachian tube into nasopharynx.

18
Q

consequences of compromising Eustachian tube function?

A

PAIN as pressure build up as can’t equlibrate pressures between middle ear and atmosphere
Infection risk and may compromise hearing ability as can’t drain secretions from middle ear

19
Q

embryological origin of eustachian tube?

A

1st pharyngeal pouch (endoderm)

20
Q

innervation of nasopharynx?

A

maxillary division of trigeminal nerve

21
Q

how do central auditory paths differ from other sensory systems?

A

have bilateral representation of sounds i.e. input from both ears reaches the auditory cortex in the temporal lobe in both cerebral hemispheres.

22
Q

other than conduction by the auditory ossicles, how else can sound be conducted to the inner ear?

A

through the temporal bone- but this is much less efficient than going via the auditory ossicles. However, if conductive hearing loss, sound will travel better by BC, giving a rinne -ve test.

23
Q

how does stapedius reduce sound intensity, protecting the inner ear from large noises?

A

pulls stapes away from opening into internal ear

24
Q

3 fluid filled spaces in cochlea?

A

scala vestibuli
scala tympani= these 2 are part of bony labyrinth, contain perilymph.
cochlear duct= part of membranous labyrinth, contains endolymph.

vestibular membrane separates scala vestibuli and cochlear duct
basilar membrane separates scala tympani and cochlear duct

25
Q

what does the oval window open into?

A

the scala vestibuli

the round window opens into the scale tympani

26
Q

how are the auditory receptors along the basilar membrane stimulated?

A

inward and outward movements of stapes produces perilymphatic pressure waves between scala vestibuli and scala tympani, setting the cochlear duct into motion, which as it rests on the basilar membrane, also sets this into motion. Movement of basilar membrane stimulates auditory receptors, and mechanically amplifies sound. The oscillations are in a sequential manner, with higher frequencies (higher tone sounds) detected more proximally.

27
Q

how do membrane potentials of hair cells change with movement of the basilar membrane?

A

stereocilia project from hair cells, and tips of the longest stereocilia are in contact or embedded in overlying tectorial membrane, so when basilar membrane moved with fluid movmement in scale tympani, stereocilia bend, and this changes Ems of hair cells.

28
Q

which cells play the major role in discriminating sounds of different frequencies?

A

inner hair cells as each has a 1:1 synaptic relationship with as many as 20 spiral ganglion cells which innervate the inner hair cells.

29
Q

how does hair cell depolarisation take place?

A

stereocilia on hair cells bent following movement of the basilar membrane.
bending stereocilia open ionic channels in the apical membrane of the cilia, causing K+ influx from endolymph in the scale media. The depolarisation opens VOCCs in base of hair cells, and Ca2+ influx triggers neurotransmitter release. This activates afferent nerve endings of of spiral ganglion neurones, allowing AP propagation into CNS.

30
Q

where does neural coding of frequency and loudness of sound occur primarily?

A

in inner hair cells which have multiple synaptic connections with spiral ganglion afferents.

31
Q

how can an acoustic neuroma be responsible for facial drooping?

A

this is a tumour which almost always arises from part of vestibular nerve in the IAM.
Tumour spreads after initial growth, causing progressive sensori-neural deafness with cochlear nerve involvement, disequilibrium with vestibular nerve and facial wkness due to involvement of facial nerve which travels through IAM to enter the facial canal in the middle ear.

32
Q

what is presbycusis?

A

age related hearing loss

33
Q

define the auditory pathway

A

1st order neurones in spiral ganglion, and their dendrites synapse on hair cells of spiral organ of Corti.
central processes of these form cochlear nerve which enters IAM to travel to brainstem.
cochlear nerve terminates on 2nd order neurones in cochlear nuclei in brainstem.
all decussate after forming 3 acoustic striae and travel to midbrain, where synapse.
fibres then termiante in medial geniculate nucleus in thalamus. Auditory radiation then travels to primary auditory complex.

accessory nuclei in path= superior olivary nucleus, nuclei of trapezoid body and nuclei of lateral lemniscus.

34
Q

what do unilateral lesions in spiral organ, cochlear nerve or cochlear nuclei cause?

A

ipsilateral deafness

distal to cochlear nuclei results in virtually no loss of hearing as bilateralism of auditory impulses as they ascend in the brainstem.

35
Q

how does a cochlea implant help with sensory-neural hearing loss?

A

can stimulate spiral ganglion cells even if hair cells lost