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Neuroscience > Touch and Hearing (mechanosensation) > Flashcards

Touch and Hearing (mechanosensation) Flashcards

1
Q

what are the different variations of touch?

A

touch is not well understood but can differentiate between gentle and more severe touch

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2
Q

what do mechanosensory neurons generate in response to touch?

A
  • rapid ionic currents
  • in Abeta fibres
  • sugests neuronal activation is likely to be direct gating of an ion channel
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3
Q

what channels have been assocaited with touch?

A
  • TREK, TRPS, Degenerin/Emac, Piezo
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4
Q

how were the channels associated with touch identified?

A
  • via mutant screens in model organisms give general principals of mechanisms
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5
Q

how is touch organised in C.elegans?

A
  • PVD covers the body
  • sensroy neurons for different touch
  • current is passed by C.elegans PVD sensory neurons in response to touch
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6
Q

what are PVDs?

A
  • are touch sensitive

- found within the hypedermic

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7
Q

how do PVDs function?

A

deflection upon pressure causing movement of the branched structure

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8
Q

what is the proposed opening of channels in the branch points in C.elegans?

A
  • as the touch is applied
  • deflects the dendrites
  • action potentials are generated
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9
Q

what occurs as a result of detection due to deflfection in C.elegans?

A

amplification
detection
transmission

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10
Q

what touch do C.elegans respond to?

A
  • harsh touch, reversal in the usual sinusoidal movement
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11
Q

how were C.elegans screened for touch mutants?

A
  • mutants generated by mutagenesis
  • antimals negatively reponding to touch will be kept, bred and re-tested
  • used geneting mapping and recombination with strain in mutants against a related
  • mapping of the mutant phenotype
  • mutants were characterised, cloned and identified
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12
Q

what did they identify in C.elegans for touch sensitivity?

A

a MEC complex

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13
Q

what is the structure of the MEC complex?

A
  • 3 components
  • in the ECM: large domain stiff proteins, roped, globular structures
  • 3 channels: MEC4, MEC6 MEC40, a complex - ion channels
  • inside the cell: MEC7,MEC12, components of microtubules
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14
Q

what is the mechanism for touch sensitivity in C.elegans?

A
  • mechanism where a channel is anchored to the cytoskeleton and the ECM
  • pressure causes movement between the two structures and physically opens the channel
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15
Q

what is the strutcure of the channel involved in touch sensitvity in C.elegans?

A
  • cystein rich domains in the extracellular loop act as a gate on the channel so normally blocked
  • extracellular loop binds to the matrix and cytoskeleton and moves the cystiene rich domain out of the way
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16
Q

what is the result of mutations at residue A713?

A
  • causes death of neurons
  • first idendified at MEC4
  • alanine to valine substituion at 713
  • alanine (small aa)
  • valine (bulky), acts to keep the channel constituviely open
  • sensory dies by excitotoxicity
  • degenerins
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17
Q

how do hairs affect touch?

A

they are the tranducers of touch

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18
Q

what is the function of hairs?

A
  • act as a levers
  • sit in a socket
  • can be attached to a neuron via the neuronal dendritic cap
  • deflection of the hair by touch moves the dendritic cap to activate a current in the neuron
  • can be direct or indirect
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19
Q

how are mouse whiskers tranducers of touch?

A

mouse whisker follicle hair is associated with merkel cells

  • upon deflection of the hair deflects merkel cells and activates associated sensory afferent neurons
  • merkel cells are acting as mechanosensors
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20
Q

what is the molecular mechanosensory in mice?

A

Piezo

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21
Q

what happens in mice genetic KO of the Piezo2 channel?

A
  • diminishes sensroy afferent response to hair defelction in whisker follicle cells
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22
Q

what is the function of Piezo2 in mice?

A
  • rapidly inactivateing piezo2 channels confers mechanosensitivity to Merkel cells
  • Piezo2 is in the slowly adapting type 1 neurons which are also mechanosensitive
  • Merkel cells release NTs from dense core vesicles to slowly adapting type 1 aferents
23
Q

what are Piezo channels?

A

can generate current in mechanically deflected membrane

24
Q

how have experiments proved the function of piezo channels?

A
  • when piezo proteins are expressed in non-mechanosensitive cells current is generated by positive or negative pressure
  • cells not expressing piezo proteins do not generate in response to positive/negative pressure
  • respond to a deflection of the membrane
25
Q

what happens if you KO piezo channels in drosophila?

A
  • drosophila only have 1 type of piezo channel
  • KOs of piezo are less sensitive to harsh touch than wild types
  • larvae would normally roll away from harsh touch but the knockouts dont respond
26
Q

what are Piezo channels specific for?

A

harsh touch

27
Q

what are the main principles of hearing?

A

vibrations of an object cause the surrounding air to condense and rarify waves travelling at 700mph

28
Q

what soundwaves can humans detect?

A

30Hz to 20,000 Hz and amplify volume 100 fold

29
Q

what do differences in the physical dimensions of sound result in?

A

differences in perceptual dimension

30
Q

what are the factors of sound?

A
  • amplitude (loudness)
  • frequency (pitch)
  • complexity (timbre)
  • also get direction from having 2 ears
31
Q

why does the ear differentiate sounds?

A

to detect individual component frequencies of complex sounds

32
Q

how does the ear direct sound?

A
  • channels sound towards detection mechanism
  • towards the tympanic membrane
  • sound vibrates the tympanic membrane
  • moves the auditory ossicles
  • ossicles transmit the vibration to the inner ear (particularly the cochlea)
33
Q

how does sound travel in the cochlea?

A
  • makes ossicles move vibrating the oval window (in the membrane which attaches to the scala vestibuli)
  • moves the sound into liquid
  • vibration in the fluid then travels around the cochlea
34
Q

why does the cochlea move the sound into liquid?

A
  • fluid is incompressible

- sound moves much more quickly

35
Q

what does th oval window allow?

A
  • vibration
  • outlet for compression
  • if you didnt have an outlet of pressure your cochlea would burst
36
Q

where does the vibration travel to?

A

enters the cochlea travels through the scala vestibuli and is detected in the organ of corti

37
Q

how is sound detected in the cochlea?

A
  • as vibration moves it becomes a travelling wave
  • point of maximum displacement of the wave describes a loaction in the cochlea
  • each frequency generates a peak at different positions along the choclea
  • achieved through hair cells
38
Q

what are the hair cells in the cochlea?

A
  • inner and outer hair cells between the tectorial and basilar membranes
  • vibrations of the cochlea causes a shearing force
  • the hairs are displace
39
Q

what is kinocilium?

A

made of microtubules

40
Q

what is sterocilium?

A

made of actin filaments

41
Q

what do kinocillium and sterocillium respond to?

A
  • respond to shear stress induced by vibration moving the tectorial and basilar membranes
42
Q

why are ankle and tip links important?

A
  • ankle links anchor at the base

- tip links: anchor and cause the opening of channel

43
Q

what are tip links?

A

molecular link between stero cilium and kinocilium

44
Q

what is the structure of tip links?

A
  • made of cadherin proteins
45
Q

what is the role of tip links?

A
  • vibration moves and tips the sterocilia toward the kinocilium
  • stretches the tip link and opens
46
Q

what are CDH23 and PCDH15?

A
  • link to a channel complex
  • long proteins linked to the cytokseleton
  • dont know the composition of the channel
47
Q

what do mutations of CDH23 and PCDH15 linked to?

A
  • ushers syndrom

- familial deafness

48
Q

what does stretching of the tip links allow?

A
  • movement of K+ and lymph into the cell
  • causes a depolarisation
  • influx of Ca2+
  • release of neurotransmitter onto an afferent neuron
49
Q

how do insects hear?

A
  • in the antenna

- movement/vibration of the 3rd antennal segment rotates the segment within the antennal segment 2

50
Q

what is involved in stretching structures called scolopales?

A
  • complex makeup
  • neurons with dendrites stretched inside them
  • in the cilium there are 3 TRP channels
51
Q

what are the 3 TRP channels in hearing in insects?

A

nanchung, inactive and nompc

52
Q

what is the role of TRP channels in the hearing of insects?

A
  • contribute to signal amplification and feedback control in insects
  • mechanosenstitve hearing cells produce vibrations in the absence of sound
53
Q

what is the role of nanchung and inactive?

A
  • dampening of vibration amplification, controlling feedback
54
Q

what is the role of Nomp C?

A

contribute to production of vibration promoting feedback

Neuroscience (11 decks)

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