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Z MD1 neurology > Hearing and ear anatomy > Flashcards

Hearing and ear anatomy Flashcards

1
Q

what are the components of the outer ear

A

auricle, external auditory meatus and tympanic membrane

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2
Q

what is the function of the outer ear

A

collection of sound and localising where the sound came from

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3
Q

explain the structure of the external auditory meatus

A
  • lateral 1/3 is cartilagenous - medial 2/3 is bony - lined by hairy skin and Cerumen glands
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4
Q

what is the function of the cerumen glands of the ear

A

prevent maceration of skin from water if it is in the canal

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5
Q

explain the nerve supply to the outer ear

A
  • posterior and inferior walls are innervated by the vagus - anterior and superior walls are innervated by the auricular temporal nerve (branch of the 3rd division of the trigeminal nerve
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6
Q

why can people with ear pain also experience tooth pain and vice versa

A

because the auricular temporal nerve (branch of the 3rd division of the trigeminal nerve) supplies both the external acoustic meatus and the temporo-mandibular joint near the teeth

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7
Q

what is the convexity of the tympanic membrane

A

concave externally and convex internally

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8
Q

what is the function of the tympanic membrane

A

vibrates at the same frequency and an amplitude relative to the sound wave –> transmits this energy into the middle ear and beyond

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9
Q

what causes the “bulge” in the tympanic membrane

A

the handle of malleus bone

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10
Q

when you shine a light into the ear… where should you see a cone of light

A

in the antero-inferior quadrant of the tympanic membrane

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11
Q

what does it mean if you see a cone of light not in the antero-inferior quandrant of the tympanic membrane

A

that the patient has a build up of pressure in the middle that is changing the concavity of the tympanic membrane (problem with the middle ear)

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12
Q

where is the middle ear

A

extends from the tympanic membrane to the petrous part of the temporal bone

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13
Q

what are the two parts of the middle ear

A

the epitympanic recess the tympanic cavity proper

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14
Q

What are the two “communications” of the middle ear

A
  • mastoid air cells - auditory tube
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15
Q

what is the function of the epitympanic recess of the middle ear

A

it communicates with the mastoid air cells of the mastoid bone

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16
Q

what is the function of the auditory tube

A

allows communication of the middle ear to the atmosphere through the nasopharynx - allows for equalisation of pressure

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17
Q

what is the direction of the auditory tube in an adult

A

antero-inferiorly to the nasopharynx

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18
Q

what happens if the auditory tube is blocked

A

middle ear cannot equalise and damage may occur to the tympanic membrane. Can have infection in the middle ear

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19
Q

what is the consequence of an infection of the middle ear

A

inflammation of the middle ear –> impact the movements of the bones of the inner ear - problem with hearing

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20
Q

why is it easier for infants to get middle ear infections

A

because their auditory tubes are more horizontal until the face of the shape changes with age - harder to drain the middle ear - easier for bacteria to migrate up

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21
Q

what are grommits?

A

a tube put through the tympanic membrane to release the pressure in the middle ear

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22
Q

what is the long term consequence of multiple chronic ear infections during infancy

A

will end up having language development delay

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23
Q

what are the three bones of the middle ear

A

malleus incus stapes

24
Q

where are the bones of the middle ear

A

attached laterally to the tympaic membrane (via malleus) and medially to the oval window of the petrous bone (via stapes)

25
what is the function of the bones of the middle ear
vibrate to transmit the sound to the nerves --\> brain --\> sound
26
what are the 2 muscles attached to the bones of the middle ear? What are their innervation? And what are they attached to?
stapedius (CNVII) - attached to stapes bone tensory tympani (CNV) - attached to malleus
27
what is the function of the little muscles in the middle ear
to dampen down the amplitude of the vibration of the sound when a noise is excessive to prevent damage
28
how do the stapedius and tensor tympani dampen down sound
large movement of the inner ear bones causes them to contract and therefore the bones cant vibrate as much --\> dampening down the energy taken through to the inner ear
29
name one example of a condition where the muscles in the inner ear are unable to dampen down sound amplitude
acoustic neuroma - compresses VII - stapedius unable to contract with loud sound
30
what are the 3 important landmarks of the medial wall of the middle ear
- oval window - stapeus attaches to it - round window - opening of middle ear back out to outer ear - promontary - basal turn of cochlea pressing onto the medial wall
31
what nerve runs through the middle ear
chorda tympani (branch of the facial nerve - carrying PNS fibres to the salivary glands and bringing back info about taste)
32
what are the two parts of the cochlea and what is the lymph associated with each called
bony labyrinth - perilymph membranous labyrinth - endolymph
33
where is the inner ear
within the petrous part of the temporal bone
34
what is the function of the semicircular canals of the inner ear
equilibrium, and telling you where your head is (ampulla)
35
what is the membranous labryrinth
a closed sac filled with endolymph within the bony labyrinth
36
where are the 3 sites of sensory receptors in the inner ear
ampulla - sensory receptors for dynamic equilibrium cochlear duct - sensory receptors for hearing utricle - sensory receptors for static equilibrium
37
what are the equivalents for the following in sound terms: wavelength amplitude waveform
wavelength: pitch amplitude: loudness waveform: tone/timbre
38
what is the major function of the ossicles
impedence matching - translate the information of the sound wave in air to a sound wave in fluid to the inner ear
39
how does the ear prevent the reflection of the sound wave on water
because of the difference in size of the tympanic membrane compared to the oval window --\> massive amplification of the signal
40
what are the 3 chambers of the inner ear
scala vestibuli scala media scala tympani
41
what are the 3 important components for hearing in the inner ear
hair cells basilar membrane tentorial membrane
42
explain the topography of the basilar membrane
wider at the apex than at the base base - responds to high frequencies apex - responds to low frequencies
43
where are the hair cells of the ear
sandwiched between the basilar membrane and the reticular lamina
44
what is the mechanism for sound collection --\> hair cells moving
sound --\> tentorium vibrates --\> ossicles vibrate --\> pressure on the oval window --\> fluid in inner ear vibrates --\> basilar membrane moves in response --\> shear force of the tentorial membrane against the hair cells --\> neuronal signalling
45
how is a neuronal signal produced
movement of the sterocilia towards the kinocilium --\> complete opening of the potassium channels --\> influx of K+ = depolarisation (if sterocilia move the opposite way --\> channels close --\> hyperpolarisation)
46
explain the asymmetric mechanoelectrical transduction by hair cells
the hair cells tend to want to depolarise rather than hyperpolarise (larger change in voltage with change in position for depolarisation compared to hyperpolarisation)
47
how is the potassium gradient set up for the influx into hair cells
sella media has a high K+ conc (endolymph) while sea tympani has a low K+ conc (perilymph)
48
what are the different roles of the inner and outer hair cells
inner - neuronal signalling outer - amplify the movements of the basilar membrane b contracting (depolarised) or elongating (hyperpolarised)
49
how can aminoglycosides cause hearing loss
cause loss of outer hair cells
50
what is the pathway for hearing
ear --\> hair cells --\> CNVIII --\> spiral ganglion --\> cochlear nucleus in medulla and superior olive --\> lateral lemniscus --\> inferior colliculus of midbrain --\> medial geniculate nucleus of thalamus --\> auditory cortex of the temporal lobe
51
where is information from the two ears integrated
in the superior olivary complex
52
what components are in the superior olivary complex
lateral superior olive - senses intensity differences medial superior olive - senses time differences trapezoid body
53
how does the brain integrate low frequency sound in the horizontal plane
neurons come from both L and R ears Whichever neuron has the biggest signal in the medial superior olive - tells us whether the sound comes from the L or R ear
54
how does the brain integrate high frequency sound in the horizontal plane
stimulatory neurons come from both L and R ears to the lateral superior olives Inhibitory neurons project contralaterally across to trapezoid body (bigger stimulatory signal = bigger inhibitory signal) Which ever net excitation is higher = sound coming from that side of the body
55
where is the auditory cortex
Heschls gyrus (within the lateral sulcus of the temporal lobe)

Z MD1 neurology (17 decks)

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