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Neuroanatomy > Auditory > Flashcards

Auditory Flashcards

1
Q

Describe what a sound wave is, physically.

A
  • Vibrations cause alternating compression and decompression of the surrounding air.
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2
Q

What is sound’s unit of intensity? What about for human speech?
Frequency?

A
  • dB, log scale (speech = 65 dB)

- Hz

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3
Q

Tensor tympani m: innervation and function?

A
  • Trigeminal n. (CN V)
  • Reduces perceived amplitude of sound. If you’re in really loud environment, it can pull on TM which pulls hand of malleus, therefore the malleus moves less sound is attenuated
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4
Q

Stapedius m: innervation and function?

A
  • Facial n. (CN VII)

- Helps suppress explosive or very large sound (so you don’t dmg the inner ear complex) by pulling on stapes bone

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5
Q

Why might you not easily see the TM when you look in the external auditory canal?

A

It sits at a 45 degree angle

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6
Q

In what part of what bone is the middle ear found?

A

Petrous portion of the temporal bone

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7
Q

How does the middle ear communicate w/the nasopharynx?

A

Auditory/eustachian/pharyngotympanic tube

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8
Q

What’s an infection to the middle ear called?

A

Otitis media (inflammation; difficult to move the fluid that exists there)

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9
Q

What larger n. runs directly deep to the TM?
What other, smaller nerve can be found there, associated w/the TM?
(what CN branches are each from)

A
  • Corda tympani (branch of VII)

- Tympanic n. (branch of IX)

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10
Q

What is hyperacusis?

Damage to which CN would cause it?

A
  • Perceiving sound to be overly loud
  • Dmg to CN VII
    (stapedius doesn’t work, so tensor tympani overcompensates…leads to pain/overactivation)
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11
Q

Which ossicle is visible on exam of the TM?

What is the name for the distal end of the fold created by said bone?

A
  • Malleus

- Umbo (not part of malleus)

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12
Q

The inner ear is composed of ___________ and __________ labyrinths.

A
  • Bony

- Membranous

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13
Q

The bony labyrinth is filled w/___________, the membranous labyrinth is filled w/__________.

A
  • Perilymph
  • Endolymph
    (both continuous w/structures in the vestibular system)
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14
Q

What are the names of the parts of the semicircular canals?

Which of the ossicles is closest to it?

A

Anterior, lateral, posterior semicircular canals and ducts

- Stapes

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15
Q

The semicircular canals lead into the _________, followed by the _________, which is connected to the cochlea.

A
  • Utricle

- Saccule

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16
Q

The apex/distal tip of the cochlea is called the ____________.

A

Helicotrema

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17
Q

What are the 3 transduction platforms for pressure waves to be transduced in the ear?

A
  1. Air–poor conduction (95% reflected)
  2. Bone conduction (osseous)–not that good
  3. Ossicular–most efficient
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18
Q

What is the “hearing structure” of the ear?

What is the name of the structure it is contain w/in?

A
  • Cochlea

- Modiolus

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19
Q

What are the names of the ascending and descending pathways of the cochlea?

A

Ascending - Scala vestibuli (oval window)

Descending - Scala tympani (round window)

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20
Q

What lies b/w the scala vestibuli and scala tympani?

What important membrane sits below it?

A
  • *Cochlear duct (scala media; membranous labyrinth)

- Basilar membrane

21
Q

What specific part of sound is measured by how far along the sound wave makes it up the cochlea?
What specific part of sound is measured by the hair cells themselves?

A
  • Frequency (*tonotopic map)

- Amplitude

22
Q

Where is the basilar membrane widest? Stiffest?

Which ends of the cochlea interpret higher vs. lower frequencies?

A
  • Helicotrema; base

- Helicotrema: low freq; base: high freq

23
Q

Where is the organ of Corti?

What takes place here?

A
  • Sitting on the basilar membrane

- Transduction of the pressure waves

24
Q

What important sensory cells are found in the organ of Corti, what is it their shape and spatial arrangement?

A
  • 1 row of inner hair cells

- 3 rows of outer hair cells (4 or 5 closer to apex), shaped like a “V” (large SA)

25
Q

What sits on top of the hair cells?

A

Gelatinous tectorial membrane

26
Q

Regarding outer hair cells of the cochlea:

  1. Which aspect of sound are they sensitive to?
  2. Explain con-/di-vergence pattern w/bipolar cells
  3. Function?
  4. Are they modified neurologically?
A
  1. Displacement sensitive
  2. Highly convergent (10 to 1) to bipolar cells
  3. Only 10% of info from cochlea comes here, so not really important for hearing, more w/fine-tuning)
  4. Can adjust their stiffness themselves based on their displacement (unique in body!). CNS can also adjust.
27
Q

Regarding inner hair cells of the cochlea:

  1. Which aspect of sound are they sensitive to?
  2. Explain con-/di-vergence pattern w/bipolar cells
  3. Function?
  4. Are they modified neurologically?
A
  1. Velocity sensitive.
  2. Divergent (1 cell goes to 10 bipolar cells)
  3. Short and stiff, used primarily to detect sound
  4. NOT modified by CNS.
28
Q

Bending of hair cells towards the kinocilium has what effect on the cell?
What about bending away from the kinocilium?
*How is the specific degree of amplitude (intensity) of the sound measured by the hair cell?

A
  • Toward: opens K+ channels, K+ in, depolarization
  • Away: closes K+ channels, hyperpolarization
  • The amplitude/intensity of the sound depends on the degree to which the hair cells move
29
Q

What cochlear cells release the first AP?

A

*Bipolar cells (not the hair cells)

30
Q

Why is a person unlikely to go deaf via CNS problems?

A

Because of the bilaterality of the system above the cochlear nuclei

31
Q

Explain the sound pathway from the outer ear to cochlea.

A
  1. External auditory canal
  2. TM
  3. Malleus > incus > stapes
  4. Oval window
  5. Scala vestibuli > scala tympani (cochlear duct b/w)
  6. Round window
32
Q

Explain the major neural players in the pathway from the cochlea to the cerebral cortex.

A
  1. Inner/outer hair cells of cochlea
  2. Bipolar cells (1st AP)
  3. Cochlear nuclei
  4. *Lateral lemniscus
  5. Inferior colliculi (midbrain)
  6. Medial geniculate nucleus (thalamus)
  7. *Heschel’s gyrus (primary auditory cortex)
33
Q

What is the approximate frequency range of the cochlea?

A

500 Hz (apex) to 16,000 Hz AKA 16 kHz (base)

34
Q

What is the Brodmann’s area # associated w/Heschel’s gyrus (primary auditory cortex)?

A

Brodmann’s area #41

35
Q

What reflexive spinal tract will we learn about that is located in the inferior colliculus and allows us to turn our head in response to a startling sound?

A

Tectospinal tract (associated w/MLF)

36
Q

Where, spatially, would you find the cochlear nuclei?

A

Rostral medulla, lateral to inferior cerebellar peduncles

37
Q

What is temporal resolution in hearing?

What is the term for how this is achieved in hair/bipolar cells, and what does this entail?

A
  • Precision of a sound measurement w/respect to time

- Phase locking: cells fire a burst of APs at initation (to cue CNS) and hyperpolarize at offset

38
Q

Explain the 2 methods the CNS uses to localize sound.

A
  1. Intra-aural difference: there’s a 50 microsecond max delay of sound b/w ears (similar w/vision)
  2. Pitch and intensity changes: as sound moves toward us, pitch + intensity increase (and vice versa)
39
Q

What are the Brodmann’s numbers for Broca’s and Wernicke’s areas?
What are their general functions?

A
  • Broca’s area: #45 (44 as well?). Motor speech.

- Wernicke’s area: #22. Speech comprehension (integrates w/all other senses coming in)

40
Q

Lesion to Wernicke’s area would result in?

What if it extends into the PTO (parietal/temporal/occipital association areas)?

A
  • Failure to comprehend auditory signals

- If it extends into PTO, visual input may be affected

41
Q

Lesion to Broca’s area would result in?

A
  • Disruption is speech production/output (but victim can still comprehend everything)
42
Q

What is the name of the tract connected Broca’s to Wernicke’s areas?
Lesions of this would result it?

A
  • Arcuate fasciculus

- Disrupted verbal output

43
Q

Which one of the following events is elicited by the mechanical displacement of the cochlear hair cell stereocilia towards the kinocilium?
A. There is an influx of K+ (potassium) through the membranes of the cilia, which is followed by an influx of Ca2+ (calcium) through the voltage-gated Ca2+ channels.
B. The hair cells on which the cilia are located are hyperpolarized.
C. Efflux of Ca2+ (calcium) through the voltage-gated channels located in the hair cell membrane occurs.
D. An inhibitory transmitter (probably gamma aminobutyric acid) is released by the hair cell.
E. There is an influx of Na+ (sodium) through the membranes of the cilia, the hair cell is depolarized, and an action potential is elicited in the afferent nerve terminal.

A

A. There is an influx of K+ through the membranes of the cilia, which is followed by an influx of Ca2+ through the voltage-gated Ca2+ channels.

Mechanical displacement of the stereocilia (e.g., in lateral direction) causes an influx of K+ (potassium) through their membranes, the hair cell is depolarized, and there is an influx of Ca2+ (calcium) through the voltage-sensitive Ca2+ channels in their membranes

44
Q

A 47-year-old woman was admitted to a local hospital after complaining of a gradual loss of hearing in one ear over time. In addition, the patient also reported some unsteadiness in balance that developed after the initial hearing loss. A magnetic resonance imaging (MRI) scan and a thorough neurological examination further revealed a facial palsy and a loss of corneal reflex on the side of the face ipsilateral to the hearing loss. The most likely cause of this disorder as revealed by the MRI and clinical evaluations was:

A. A tumor in the region extending from the external to the middle ear
B. An acoustic neuroma of the cerebellopontine angle affecting cranial nerve VIII
C. A vascular occlusion affecting the medial two thirds of the basilar pons
D. A tumor affecting the midline region of the cerebellar cortex
E. A vascular lesion involving the medial longitudinal fasciculus and adjoining regions of the dorsal pons

A

B. An acoustic neuroma of the cerebellopontine angle affecting cranial nerve VIII

Ipsilateral hearing loss coupled with some loss of balance and with facial palsy and loss of corneal reflex on the same side as the hearing loss could only occur as a result of damage to CN VII & CN VIII. The most common place where this is likely to occur is the cerebellopontine angle, where an acoustic neuroma would affect not only CN VIII, but also CN VII because of its proximity to CN VIII.

45
Q

A 27-year-old man who had been in good health reported to his primary physician that he had episodes of dizziness. Over time, the dizziness tended to decrease, but the patient began to experience tinnitus and hearing loss, and both of these symptoms became progressively worse. A neurological examination revealed no other signs of neurological dysfunctions. The patient was treated with anticholinergics with some degree of success. The most likely basis of the disorder in this patient is:

A. A lesion of the medial longitudinal fasciculus
B. A tumor of the cerebellum
C. A tumor impinging on CN VIII and CN VII at the cerebellopontine angle
D. An abnormal volume of endolymph of the inner ear
E. A lesion of the dorsolateral pons affecting the lateral lemniscus

A

D. An abnormal volume of endolymph of the inner ear

Because the patient experienced both auditory and vestibular symptoms but showed no other clinical signs, the site of dysfunction had to be limited to CN VIII. Such effects are typically of peripheral origin. In this case, the patient was suffering from Ménière’s disease, which involves the inner ear, where the effects are likely manifested through alterations of endolymphatic homeostasis.

46
Q

What structure allows sound waves to enter the perilymph?

What structure allows them to leave?

A
  • Oval window

- Round window

47
Q

What n. sends AP’s to the brain from the organ of Corti?

A

Cochlea n.

48
Q

What does pitch refer to?

A

Sensation of frequency

49
Q

Explain which of the following contain perilymph and which contain endolymph:

  • Scala vestibuli
  • Cochlear duct
  • Scala tympani
A
  • Scala vestibuli: perilymph
  • Scala media: endolymph
  • Scala tympani: perilymph

Neuroanatomy (20 decks)

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