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Neuroanatomy Block 3 > Lecture 22/23: Auditory System > Flashcards

Lecture 22/23: Auditory System Flashcards

1
Q

Parts of the ear

A
  • External
  • Middle
    • External and middle separated by ear drum
  • Inner
    • Fluid filled
    • Cochlea which has hearing receptors; hair cells
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2
Q

What is the external ear innervated by?

A

Cranial nerves V, VII, and X

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3
Q

Major parts and border of the external ear

A
  • Pinna or auricle
  • External auditory meatus
  • Ends at tympanic membrane or ear drum
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4
Q

What ear are you looking at if the light reflex is on the lower right?

A

RIGHT ear

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5
Q

Middle ear structure

A
  • Air filled cavity behind drum
  • 3 bones transfer vibrations to oval window with fluid behind
  • Opens to outside world via eustasian tube
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6
Q

Inner ear structure

A
  • Fluid filled sacs within bony sacs behind an oval window
  • Has sensory hair cells for hearing and balance
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7
Q

What innervates hair cells in the inner ear?

A

Cranial nerve VIII

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8
Q

Embryonic origin of the ear

A
  • Branchial cleft 1
    • External acoustic meatus
  • Branchial pouch 1
    • Middle ear space and eustacian tube
    • Membrane between cleft and pouch 1 is ear drum
  • Branchial Arch 1
    • Middle ear bones malleus and incus
  • Branchial Arch 2
    • Stapes
  • Otic placode
    • Otic vesicle –> Hair cells and CN VIII cells
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9
Q

Where do sensory axons of the ear (CN VII and X) terminate?

A

Chief nucleus of 5 and trigeminal nucleus

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10
Q

Innervation of ear drum

A
  • Outer surface
    • V3, VII, X
  • Inner surface
    • IX
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11
Q

Purpose of middle ear bones

A

Amplify and transfer sound pressure waves

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12
Q

Two duct systems of the inner ear

A

Vestibular bony duct and Cochlear bony duct

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13
Q

Three spaces of the cochlear bony duct

A
  • Scala vestibuli
  • Scala tympani
  • Scala media (membranous labyrinth)
    • Has the hair cells
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14
Q

Reissner’s membrane

A

Separates scala media from vestibuli

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15
Q

Stria vascularis

A

Pasted to the bony wall and secretes endolymph

Part of the membranous labyrinth

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16
Q

Basilar membrane

A

On which the auditory hair cells sit, separates scala media from tympani

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17
Q

Tectorial membrane

A

Sits over the hair cells and helps to activate them

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18
Q

Path of sound wave in inner ear

A
  1. Scala vestibuli
  2. Helicotrema
  3. Scala tympani
  4. Creates pressure difference in scala media and vibrates it
  5. Responds to highest frequencies at the base, lowest at top
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19
Q

Stereocilia in inner ear

A

When the cilia bend towards the tallest one (kinocilium), ion channel is pulled open and excites auditory nerve fibers

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20
Q

Where do auditory nerves terminate?

A

Cochlear nucleus in rostral medulla

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21
Q

How many rows of hair cells are there along the basilar membrane?

A

3 outer, 1 inner

22
Q

What are outer hair cells thought to do?

A
  • Change length when near threshold amplitudes are detected
  • The hairs will change length and push on the membrane to make it vibrate more and cause more signal
23
Q

What kills outer hair cells?

A

Aminoglycoside antibiotics

24
Q

What nerve innervates the middle ear surface and inner surface of ear drum?

A

CN IX

25
Q

What muscles help protect the ear against loud sound?

A
  • Tensor tympani
    • CN V
  • Stapedius muscle
    • CN VII
26
Q

Main function of the middle ear

A

Amplify the sound waves coming in because water has a much higher density than air

27
Q

How is endolymph composition special?

A

High in potassium low in calcium

28
Q

Otoacoustic emissions

A

Vibrations of the ear drum received from the inner ear; caused by the outer hair cells changing length. Can be used to test ear function when the person can’t tell you anything.

29
Q

How are nerves arranged in the internal acoustic meatus?

A

Facial nerve top, cochlear nerve bottom

30
Q

Where do auditory nerve fibers terminate?

A

Dorsal and ventral cochlear nuclei at pons/medulla border

31
Q

Where are the signals from both ears integrated?

A

Superior olive nuclei in the pons via the trapezoid body pathway

32
Q

How do cells in the cochlear nucleus bypass the superior olive?

A

They use the lateral lemniscus to go straight to the inferior colliculus

33
Q

Where do outputs from the superior olive go?

A

Inferior colliculus

34
Q

Where do outputs from the inferior colliculus go?

A

Auditory thalamus or across the midline to the other IC

35
Q

Auditory thalamus

A
  • Also called the medial geniculate
  • Responds to sounds in both ears
  • Projects to ipsilateral auditory cortex
36
Q

Tonotopic organization

A

Neurons are organized by frequency at every point along the auditory pathway

37
Q

Wernicke’s Area

A

Language comprehension and word selection

38
Q

Arcuate fasciculus

A

Communication between Broca’s and Wernicke’s areas

Output via motor cortex to LMNs

39
Q

Lesion of Wernicke’s Area

A

Can’t understand questions

Speech has normal rhythm but is meaningless

40
Q

Lesion of Broca’s Area

A

Can understand questions but can’t produce any speech

41
Q

Lesion of arcuate fasciculus

A

Can understand language and produce speech but can’t repeat heard phrases

42
Q

Conductive hearing loss

A

Sound physically can’t reach the inner ear. Obstruction or damage to structures like ear drum or ossicles

43
Q

Sensorineural hearing loss

A

Abnormality in the cochlea or cochlear nerve (rarely cochlear nucleus)

Commonly due to loss of hair cells

44
Q

Weber Test Results

A
  • Louder in bad ear
    • Conductive hearing loss in bad ear
    • Possibly hair cells protected from outside interference by obstruction
    • Lets the vibration be received better
  • Louder in good ear
    • Sensorineural hearing loss
    • Hair cells are not being stimulated in bad ear
45
Q

Rinne Test Results

A
  • Easier to hear via air than by bone
  • Tuning fork placed on mastoid bone
    • Taken off when the pt can’t hear it anymore
    • Asked if they hear it by air
  • A normal ear will hear the sound again
  • Conductive hearing loss won’t hear the sound again
  • Doesn’t work for sensorineural hearing loss
46
Q

Presbycusis

A

Age related sensorineural hearing loss

47
Q

Auditory brainstem response

A

Can test infants’ hearing by presenting sound and recording brain waves

48
Q

Tinnitus

A
  • Perception of sound in the ear when none is present
  • Causes
    • Wax
    • Otosclerosis
    • HBP
    • Allergies
    • Diabetes
    • Thyroid problems
    • NSAIDs, antibiotics, sedatives, antidepressants
    • Increased spontaneous hair cell firing
49
Q

Objective tinnitus

A

Hearing sound from turbulent blood flow

50
Q

Meniere’s Disease

A
  • Rupture of Reissner’s membrane causing mixing of endolymph and perilymph
  • Affects one ear usually
  • Causes vertigo, imbalance, nausea, tinnitus, ear pressure, hearing loss
51
Q

Mechanism of cochlear implants

A

String of electrodes inserted into cochlea. Electrodes are activated corresponding to different frequencies.

Neuroanatomy Block 3 (18 decks)

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