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Neuroanatomy block 2 > Hearing, Taste and Smell > Flashcards

Hearing, Taste and Smell Flashcards

1
Q
  1. Onto what membrane of the cochlea do the ossicles articulate?
A

[oval window]

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2
Q
  1. What is the purpose of the middle ear?
A

[overcome the impedance mismatch problem, when air vibrations (sounds) meet fluid (e.g., endolymph) most of the energy in the vibrations is lost because fluid is much denser]

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3
Q
  1. What is the fluid in which the ‘hairs’ reside?
A

[endolymph, very high in K+]

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4
Q
  1. *Are all hair cell ‘hairs’ attached to the tectorial membrane? [
A

[no, the inner hair cells are not; the kinocilia of the outer hair cells are… which promotes the mechanical amplification of sound signals by the outer hair cells]

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5
Q
  1. What are the ‘hairs’ of the hair cell stuck into?
A

[tectorial membrane]

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6
Q
  1. What is the name of membrane on which the hair cells reside?
A

[basilar membrane]

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7
Q
  1. *What causes otoacoustic emissions?
A

[vibrations of the outer hair cells move causing vibrations of the oval window driving the ossicles and finally, vibrating the tympanum (yes, it’s backwards!!)… tells about the integrity of the outer hair cells]

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8
Q
  1. *What is the Walsh-Healy standard?
A

[thou shall not experience greater than 90 dB for an 8 hr workday… has to be one of the most ignored laws around]

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9
Q
  1. *What is the Fourier theorem?
A

[The idea that any arbitrary signal (whether sound, image, whatever) can be broken down and reproduced as a series of sine waves. This comes up because individual primary auditory ganglion can be well characterized by their tuning preference for sine waves at specific frequencies (actually characterized by sine wave frequency, amplitude, and phase). Therefore, a popular theory of hearing is that the cochlea breaks sound into their various sinusoidal components and then reconstructs (Fourier synthesis) that sound in the brain].

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10
Q
  1. Which nucleus is critical/specialized for sound source localization?
A

[superior olive]

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11
Q
  1. What two cues are available for sound source localization?
A

[the difference in timing between sounds coming into our right versus our left ear (yes, it’s a microsecond or so, amazing!), and intensity difference between sounds hitting our left vs right ear…. And the greater the distance between the ears, the better the discrimination… elephants are amazing!]

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12
Q
  1. What is the frequency range over which the human can hear?
A

[.020-20 KHz]

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13
Q
  1. What is the frequency range over which the average 50 year-old American can hear?
A

Up to 12KHz

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14
Q
  1. When we damage our cochlear hair cells, how long does it take to grow new ones?
A

[Forever]

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15
Q
  1. Are there more inner hair cells or outer hair cells
A

[outer]

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16
Q
  1. For hair cells in endolymph, bending the stereocillia towards the kinocillium will generate an ______ current, due to K+ influx
A

[inward]

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17
Q
  1. If the kinocilia were the height of the Eiffel Tower, a displacement (bend) of 3 inches would be enough to trigger the perception of a sound
A

True

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18
Q
  1. In the active theory of hearing, what is the role of outer hair cells?
A

[sound causes vibrations on the basilar membrane according to frequency (low at apex, high at base of cochlea). The vibration activates outer hair cells ‘motors’, amplifying the original vibration]

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19
Q
  1. Inner hair cells will receive input from ______ spriral ganglion fibers, a single spiral ganglion fiber will innervate __ outer hair cells
A

[ 10 , 10]

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20
Q
  1. How many spiral ganglion (primary auditory afferent) cells are there in each ear?
A

[ ~33,000]

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21
Q
  1. The ‘sweet spot’, most sensitive frequencies for primary afferents is _____
A

_____ [1-3 KHz; pretty well overlaps with the speech spectrum]

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22
Q
  1. *Are cochlear nucleus neurons monaural or binaural?
A

[monaural, but above that there will mixes from both ears]

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23
Q
  1. *Identify the bundle of cochlear fibers that cross the brainstem at the level of the cochlear nu
A

[trapezoid body]

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24
Q
  1. Identify the bundle of cochlear fibers that terminate in the inferior colliculus and nu of lateral lemniscus
A

[lateral lemniscus]

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25
Q
  1. Identify the major nuclei in the ascent of auditory fibers to neocortex (area 41)
A

[spiral ganglion, cochlear nu, nu lateral lemniscus/inferior colliculus, medial geniculate nu]

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26
Q
  1. What is another name for primary auditory cortex
A

[Brodmann’s area 41, Heshl’s gyrus]

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27
Q
  1. In what ‘lobe’ is Heshl’s gyrus?
A

[we consider it in the temporal lobe]

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28
Q
  1. Where is Wernicke’s area?
A

[superior temporal gyrus, area 22, surrounding primary auditory cortex]

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29
Q
  1. Distinguish between a kinocilia and a stereocilia
A

[each hair cell has 60-80 stereocilia, but only 1 kinocilia]

30
Q
  1. 90% of primary afferent synapses are on inner/outer hair cells
A

[inner]

31
Q
  1. How is ‘loudness’ encoded?
A

[combined high output of sensitive and less sensitive spiral ganglion cells]

32
Q
  1. What is the impedance mismatch problem in hearing?
A

[intensity loss attributable to sound passing from air medium into fluid; 30 dB loss is minimized by design of middle ear; 3 dB recovered by ossicles, ~24 dB recovered by ratio of surface areas between tympanum and oval window]

33
Q
  1. Do we hear better under water?
A

[ yes, because water is a much thicker medium than air]

34
Q
  1. How are hearing deficits usually classified?
A

[conductive (middle ear to oval window) and sensorineural (cochlea, brain)]

35
Q
  1. What is the Rinne test?
A

[determines if hearing loss is conductive or neural. Strike a tuning fork and place it against the mastoid process. When the patient can no longer feel the vibration, put the fork next to the ear. The time they can still hear the tuning fork should be > 2X the time they felt the vibration…. If less, conductive problem… hearing aid will help]
If a patient reports hearing loss, the Rinne test is of value to rule out conductive hearing loss. This is key - passing the Rinne test does not mean there is no hearing loss, it means that any hearing loss is NOT due to conductive compromises.
For example, consider a patient with sensorineural hearing loss who has a certain fraction of dead hair cells. Overall their hearing thresholds will be higher for some frequencies. The length of time that they hear the tuning fork sound through bone conduction will be shorter than a patient with normal hearing…. but they will still be able to hear the fork in the air for ~2x (or more) longer than this period because there are no conductive issues with the middle ear.

36
Q
  1. What is the Weber test?
A

[used to dissociate conductive, neural hearing loss. Strike a tuning fork and place at the vertex of the head. The sound should be symmetric. If asymmetric, the louder sound is associated with the defective ear… conductive issue and hearing aid will help]

37
Q
  1. What is tinnitus?
A

[‘Ringing’ in the ear. Common in older people. One type is simply the aftermath of loud sounds, e.g., the ringing the day after going to a rock concert. The other type has variable onset, and can last for years. High doses of aspirin can also induce tinnitus]

38
Q
  1. *How do cochlear implants restore hearing? [
A

[They’re amazing! For people that have extensive hair cell loss, but the spiral ganglion dendrites are still in cochlea, the surgeon threads a fine multistrand wire (12-16 wires in the bundle) into the cochlea and connects the wires to a microprocessor that then sends electrical impulses to the different wires, and voila! Sound! It can be so good that the recipient can talk on the phone!]

39
Q
  1. What is the upper frequency your average 50 year old can hear?
A

12Kz

40
Q
  1. Identify an antibiotic that kills hair cells
A

[Gentamycin, streptomycin

41
Q
  1. Identify the ‘order’ of neurons in ascent to the auditory cortex
A

[spiral ganglion 1st order, cochlear nucleus 2nd order (trapezoid body, lateral lemniscus fiber bundles), inferior colliculus 3rd order (brachium of inferior colliculus), medial geniculate body 4th order (internal capsule), auditory cortex.]

42
Q
  1. How many different types of receptors are there for odorants?
A

[~1000 ]

43
Q
  1. How many different types of receptors does each olfactory receptor cell express, and are they ionotropic or metabotropic?
A

[it would appear 1; all of the receptors appear to be metabotropic]

44
Q
  1. Are olfactory receptor cells CNS or PNS?
A

[PNS]

45
Q
  1. What is the sensitivity of smell?
A

[< 1 part/billion]

46
Q
  1. What is a ‘glomerulus’ in the olfactory bulb?
A

[a network of dendrites where primary afferents terminate. Apparently, neurons sharing the same receptor type converge on the same glomerulus]

47
Q
  1. *Identify the 2 types of neurons contributing axons to the olfactory tract
A

[mitral cells, tufted cells]

48
Q
  1. Identify major targets of the olfactory tract?
A

the tract projects directly to piriform, periamygdaloid and entorhinal cortex - Periamygdaloid provides smell direct access to amygdala (e.g., fear of fox urine in rodents), entorhinal cortex provides smell direct access to hippocampus (learning)

49
Q
  1. Which sense has no thalamic ‘relay’?
A

[olfaction]

50
Q
  1. Do olfactory bulb axons synapse in neocortex?
A

[No, but they do synapse in cortex (allocortex)]

51
Q
  1. Where does one observe neurons whose activity is modulated by both taste and smell?
A

[orbitofrontal cortex]

52
Q
  1. *What is entorhinal cortex?
A

[it makes up the bulk of the parahippocampal gyrus, is the major input into the hippocampus, and receives directly from the olfactory bulb)

53
Q
  1. *How large is our olfactory ‘vocabulary’ (# of distinct smells we can discriminate)?
A

[well over 1000]

54
Q
  1. *Can dogs be trained to discriminate individuals who have cancer?
A

[yes, C. elegans can respond to cancer cells in urine at extremely low levels as well]

55
Q
  1. What is anosmia?
A

[lacking the sense of smell]

56
Q
  1. *What is an ‘aura’
A

[A perceptual experience, usually smell or taste, that immediately precedes and predicts certain types of epileptic seizures associated with the limbic/temporal lobe]

57
Q
  1. *Is continual neurogenesis necessary for olfaction?
A

[Yes. Circuits within the olfactory bulb (CNS) and hippocampus depend on neurogenesis to function properly. Should this process stop, the risk factor for both Parkinson’s and Alzheimer’s disease goes up significantly. Having said that, a significant fraction of the population over 60 loses its ability to smell (anosmia).

58
Q
  1. *What is the ‘satellite’ olfactory structure associated with pheromones?
A

[vomeronasal organ; it seems a continuous debate as to whether humans have one. Maybe not, but we do seem affected by them, even if it’s not nearly the degree to which it affects our non-human friends]

59
Q
  1. How long do olfactory receptor cells last?
A

[they seem to exist for ~45 days are so, emerging from basal cells in the olfactory mucosa]

60
Q
  1. How many taste receptor types are there? [
A

[probably 5: sweet, salty, bitter, acid, umami. Several exploit ionotropic channels (e.g., Na+), use ionotropic receptors, or use both (ionotropic and metabotropic)]

61
Q
  1. Are taste receptor cells neurons?
A

[hard to say, but they are PNS. They have no processes, and they turn over ~14 days. They just seem to leak more or less glutamate onto the primary afferents (from VII, IX, X) depending on their polarization state]

62
Q
  1. Do single taste receptor cells contain a variety of receptors?
A

[Yes, so that is different from olfaction]

63
Q
  1. What is the relationship between receptor cells and taste ‘buds’?
A

[taste buds are invaginations and contain 50-60 taste receptor cells, innervated by dendrites from VII, IX, X. Taste buds are located in papillae, outcroppings of the tongue. Each taste bud can be sampled by several dendrites]

64
Q
  1. Which cranial nerves convey taste?
A

VII, IX, X]. VII samples the anterior 2/3 of the tongue. These dendrites rode with the lingual nerve (V3) to get out on the tongue, and their cell bodies are in the geniculate ganglion. Axons of taste fibers all converge in the ipsilateral rostral division of the nucleus of solitary tract. SVA dendrites of IX sample the posterior 1/3 of the tongue, their cell bodies are in the inferior ganglion (aka petrosal). SVA dendrites of X are few, sampling taste receptors in pharynx, glottis and epiglottis. Their cell bodies are found in the nodose ganglion]

65
Q
  1. Are the primary tastes distributed randomly across the tongue
A

[Not exactly. There are regional preferences, but overall, one can find all five receptors across the tongue]

66
Q
  1. Do primary afferents respond exclusively to only 1 type of taste?
A

[No. They show a preference, but will typically show some response to 2, 3, or even 4 different primaries]

67
Q
  1. How do primary afferents get to ‘taste’ cortex? [
A

[Primary afferents (1st order) terminate in the rostral division of the nucleus of solitary tract. Neurons of the n solitary tract (2nd order) project to the VPMpc, a small thalamic nucleus just medial of VPM. Neurons of the VPMpc (3rd order) project to primary taste cortex, considered to be part of insular cortex.

68
Q
  1. Are there taste neurons that are highly selective for specific tastes? [
A

[Yes, but you won’t find them until you get into taste cortex]

69
Q
  1. Where do taste and smell ‘get together’
A

[In orbitofrontal cortex, and likely other places]

70
Q
  1. *Are there smells that seem to trigger innate fear?
A

[Yes, in rats and mice, the scent of fox or bobcat urine will generate freezing and a fear response. The ‘triggered’ cells appear to be in the amygdala, which makes perfect sense because of it purported role in fear]

71
Q
  1. What is learned taste aversion?
A

An extremely powerful form of learning in which one bad experience with a food causes a highly selective aversion to that food that can persist for years]

72
Q
  1. *Is it true some people just ‘have no tastes’?
A

[Yes. There can be 100-fold differences among people in the number of taste receptor cells]

Neuroanatomy block 2 (7 decks)

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