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Medical Studies 2A > 4.3 Hearing and Balance > Flashcards

4.3 Hearing and Balance Flashcards

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USMLE® Step 1 flashcards
1
Q

What property of a sound wave determines loudness?

A

Amplitude

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2
Q

What property of a sound wave determines pitch?

A

Frequency

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3
Q

What is the Confusionist name for earwax?

A

Cerumen

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4
Q

Describe the two sections of the external acoustic meatus

A
  • Cartilaginous (outer 1/3)
  • Bony (Inner 2/3)
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5
Q

Where is cerumen produced?

A

Cartilaginous component of external acoustic meatus

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6
Q

Function of cerumen

A

Stop foreign bodies/bacteria entering into middle and inner ears

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7
Q

What is the boundary between the external and middle ear?

A

Tympanic membrane

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8
Q

What is the purpose of the middle ear? Why is this important?

A
  • Amplify the sound waves before they enter the fluid-filled cochlea
  • Sound is dampened by fluid, so must be amplified to compensate
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9
Q

What is the hollow portion of the middle ear called?

A

Tympanic cavity

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10
Q

What are the three bones of the middle ear (and their more useful names)?

A
  • Malleus (Hammer)
  • Incus (Anvil)
  • Stapes (Stirrup)
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11
Q

Which two muscles are associated with which two ossicles, and which nerves innervate them?

A
  • Tensor Tympani (Malleus) CN V3
  • Stapedius (Stapes) CN VII
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12
Q

What are the components of the bony labyrinth of the inner ear?

A
  • Cochlea
  • Vestibule
  • Semicircular canals
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13
Q

What are the components of the membranous labyrinth of the inner ear?

A
  • Cochlear duct
  • Utricle
  • Saccule
  • Semicircular ducts
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14
Q

What fluids are located in the membranous/bony labyrinth?

A

Bony: Perilymph
Membranous: Endolymph

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15
Q

Describe the flow of sound through the different windows/chambers of the cochlea

A
  • Stapes transmits sound through oval window into perilymph of scala vestibuli
  • Flows to apex (i.e., centre), and then flows out through scala tympani
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16
Q

Why does sound travel from the apex back through the scala tympani and out of the oval window? Why couldn’t it just stay where it is?

A

We need to relieve the buildup of pressure, otherwise your cochleas will explode (which is slightly suboptimal).

17
Q

What are the three membranes of the scala media?

A
  • Basilar (which is embedded with hair cells)
  • Tectorial (which the stereocilia come into contact with)
  • Vetibular
18
Q

What fluid is in the scala media (hint: is the scala media located in the membranous or bony labyrinth?)

A

Endolymph

19
Q

What is the organ of Corti made of, and where is it?

A

It is made up of the hair cells that are embedded in the basilar membrane of the scala media of the cochlea of the ear.

20
Q

Describe how stereocilia movement causes neurotransmitter release, with reference to endolymph.

A
  • Endolymph is rich in K+
  • Contact with tectorial membrane opens mechanically gated potassium channels on tips of stereocilia
  • K+ rushes in, opening voltage-gated Ca2+ channels in base of hair cells
  • Triggers neurotransmitter release
21
Q

What’s the deal with auditory afferents, the spiral ganglion, and the cochlear nerve?

A
  • Sensory neurons have axons that branch up to base of hair cells in organ of Corti
  • Their cell bodies are located in a nearby spiral ganglion
  • Since they are bipolar, the second part of their axons go on top form the cochlear nerve, which then joins CN VIII
22
Q

What is the dorsal/ventral cochlear stream important for?

A

Dorsal: quality of sound (like bat vs bet vs debt)

Ventral: timing

23
Q

Outline the ventral cochlear stream pathway

A
  • Ventral cochlear nuclei
  • Some decussate at trapezoid body
  • Superior olivary nucleus
  • To Inf. Colliculi (via lateral lemniscus)
  • To MGN (via brachium of inf. colliculus)
  • To A1 (via corona radiata and internal capsule)
24
Q

Outline the dorsal cochlear stream pathway

A
  • Dorsal cochlear nuclei
  • Decussates at pontine tegmentum
  • Inf. Colliculi (via lateral lemniscus)
  • To MGN (via brachium of inf. colliculi)
  • To A1 (via corona radiata and internal capsule)
25
Q

Where must a neurological lesion be in order to cause unilateral hearing loss? Why?

A

Must be proximal to cochlear nuclei - after that point, everything is bilateral

26
Q

In which Gyrus is the primary auditory cortex located?

A

Herschl’s gyrus (superior temporal gyrus)

27
Q

True or false: the primary auditory cortex is tonotopically organised.

A

True. Like the basilar membrane.

28
Q

Where is the auditory association cortex? What does it do?

A

It surrounds A1, cortically. It is responsible for recognition of sounds (e.g., based on past experience)

29
Q

What fasciculus connects Wernicke’s and Broca’s?

A

The Arcuate Fasciculus

30
Q

Using a mnemonic, recall the passage of nervous auditory signals

A

E: Eighth cranial nerve
C: Cochlear nucleus
O: Olivary nucleus (superior)
L: Lateral lemniscus
I: Inferior colliculus
M: MGN
A: Auditory nucleus

(ECOLIMA)

31
Q

What are the two kinds of acceleration tracked by the vestibular system? What tracks them?

A
  • Angular acceleration (rotation): anterior, posterior, and horizontal semicircular canals
  • Linear acceleration (along a line): saccule (up/down), and utricle (forward/backward)
32
Q

To which part of the vestibulocochlear apparatus does the stapes transmit force?

A

The vestibule

33
Q

Describe how the semicircular canals detect rotational acceleration

A
  • Endolymph sloshes when movement is in same plane as canal
  • Sloshes against cupula
  • Pushes hair cells one way = excitation, another way = inhibition
  • Therefore, the brain can interpret the pattern of excitation/inhibition as vestibular information
34
Q

Describe how otolith organs detect gravity and other causes of acceleration

A
  • Each organ contains otoliths (calcium carbonate crystals), and hair cells, separated by a gelatinous layer
  • In response to acceleration, the crystals are pulled on, displacing gelatinous layer and activating hair cells
35
Q

What are the two sets of vestibular nuclei in the brainstem? What tracts do they form?

A
  • Lateral vestibular nuclei (form lateral vestibulospinal tract)
  • Medial vestibular nuclei (form medial vestibulospinal tract)
36
Q

What is the medial vestibulospinal tract important for?

A

Controlling head and neck position

37
Q

What is the lateral vestibulospinal tract important for?

A

Maintaining balance and extensor tone

38
Q

Where does the medial vestibulospinal tract terminate?

A

Cervical spine

Medical Studies 2A (110 decks)

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