The auditory system Flashcards

1
Q

What is the anatomy of the outer, middle and inner ear?

A
  • Outer = pinna, ear canal + tympanic membrane
  • middle = ossicles + oval window
  • inner = Vestibular system + cochlea
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2
Q

Perilymph vs endolymph

A

P: lots of sodium, low potassium (like ECF) - in bony labyrinth
E: Lots of K, low Na (like ICF) - in membranous labyrinth

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3
Q

What are the 3 chambers called inside the cochlear?

A
  • Scala tympani (bottom)
  • cochlear duct
  • Scala vestibuli (top)
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4
Q

What are the membranes called that separate the 3 chambers?

A
  • Vestibular membrane between vestibuli and duct

- Basilar membrane between duct and tympani

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5
Q

What sits on the basilar membrane?

A

Spiral organ, with the tectorial membrane lying over the top of that.

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6
Q

What is the spiral organ?

A

hair cells and pillar cells

- hair cells are the auditory receptors - have stereocilia which are responsible for sound transduction

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7
Q

What is the sound pathway in the ear?

A

Sound > Canal > tympanic membrane > ossicles > oval window > fluid vibrates in the cochlear > vibration of vest. membrane > vibration of cochlear duct > vibration of basilar membrane

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8
Q

What complications can we get in the sound pathway?

A
  • Blocked canals
  • Tympanic membrane trauma
  • Stiff ossicles
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9
Q

How is sound transduced?

A
  • when stereocilia move, they will tug on the tiplinks - transduced into an AP
  • at the base of the tiplinks are mechanically gated channels - pulled open by tip links and allow K ion influx - moves down electrochemical gradient
  • when sterocilia move towards longest cell, tip link opens the channel - causes depolarisation -> APs
  • when stereocilia move towards the smallest one, they close and hyperpolarise -> no APs
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10
Q

Detecting sounds

A
  • inner hair cells are responsible for sound discrimination

- outer hair cells physically contract, pulling the basilar membrane in such a way to amplify the sounds

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11
Q

What complications can we have with sound transduction?

A
  • Endolymphatic hydrops = increased pressure in endolymph
  • Menier’s disease = endolymphatic hydrops causes mixing of the 2 lymphs which damages inner hair cells
  • Ototoxic drugs can damage stereocilia of hair cells (irreversible) - less APs - e.g. NSAIDs, chemo, gentamycin
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12
Q

How are different qualities of sound encoded by the system?

A
  • loudness = louder sounds produce larger vibrations, bigger receptor potentials and hence more APs
  • pitch = based on the structure of the basilar membrane. At different points of the cochlea, hair cells oscillate at different frequencies
  • right in the middle of the spiral = 20Hz
  • at the end of the cochlea = 20kHz as it is more floppy
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13
Q

Complications with sound discrimination

A

Presbycusis - loss of high-frequency hearing as you get older

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14
Q

What is the primary auditory pathway?

A
  • cochlear nerve travels through dorsal and ventral cochlear nuclei
  • crosses midline to inferior colliculus
  • up to medial geniculate nucleus
  • up to primary auditory cortex on top of the temporal lobe
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15
Q

How do we localise sound?

A
  • determined by comparing the sound detected by the two ears - separate for high and low-pitched sounds
  • The lateral superior olivary nuclei compare loudness of high frequency sounds
  • the medial superior olivary nucleus compare the timing of low frequency sounds
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16
Q

Complications with sound localisation

A
  • acoustic neuroma - auditory nerve runs in the internal auditory meatus - can be damaged by SoL
  • Vestibular schwannoma - uncontrolled schwann cell growth in internal auditory meatus - nerve compression
  • 1st symptoms - unilateral tinnitus, later get dizziness and fainting.