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Biology 404 > Mechanosensation > Flashcards

Mechanosensation Flashcards

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1
Q

Detection of mechanical stimuli is also sometimes called the (1) sensory system

A

Somatic

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2
Q

Membrane receptors can be of 2 kinds:

A
  1. Lock and key receptors
  2. Force-gated receptors (stretch-activated)
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3
Q

The somatic sensory system detects primarily 2 kinds of stimuli

A
  1. Mechanical stimuli
  2. Noxious stimuli
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4
Q

The main organ of somatosensation is…

A

The skin

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5
Q

Why is the somatic sensory system important? (3)

A
  1. Identify shapes and textures
  2. Monitor internal and external forces acting on the body
  3. Detect potentially harmful stimuli

(Exploration, pain, healing)

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6
Q

Non-hairy skin is called “(1) skin”

A

Glabrous skin

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7
Q

Describe receptors in the skin, generally

A

Can have no capsule (free nerve endings), or nerve endings can be associated with some kind of associated cell

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8
Q

Free nerve endings in the skin are typically associated with detection of (1) stimuli

A

Noxious

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9
Q

What are the 4 kinds of somatosensory receptors in the skin?

A
  1. Merkel’s discs
  2. Meissner’s corpuscle
  3. Pacinian corpuscle
  4. Ruffini’s endings
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10
Q

What is the primary role of a capsule around a cutaneous nerve ending?

A

Helps to regulate the response to stimuli: When stimulus is applied to skin, the skin is deformed which activates nerve endings. The type of capsule around the nerve ending affects the ionic permeability of the cell membrane

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11
Q

Capsules around nerve endings are especially common in (glabrous/non-glabrous) skin

A

Glabrous

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12
Q

Describe rapid adaptation

A

Changes in a stimulus are encoded

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13
Q

Describe slow adaptation

A

Persistence of a stimulus is encoded

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14
Q

Which kind of subcutaneous receptor is associated with glabrous and hairy skin?

A

Merkel’s discs

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15
Q

40% of sensory innervation to the hand comes from these subcutaneous receptors

A

Meissner’s corpuscles

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16
Q

Describe the histology of Meissner’s corpuscles

A

Capsules made of connective tissue: layers of Schwann cells. These may surround one or more nerve fibers

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17
Q

Meissner’s corpuscles are (rapidly/slowly) adapting

A

Rapidly

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18
Q

What kind of mechanosensory stimulus are Meissner’s corpuscles tuned to?

A

Vibration and movement across the hand

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19
Q

Meissner’s corpusles are associated with (1) skin

A

Glabrous

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20
Q

Other than in the skin, where else can Pacinian corpuscles be found? (2)

A
  1. Gut
  2. Skeletal system
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21
Q

Describe the histology of a Pacinian corpuscle

A

Onion-like arrangement of cells with fluid between cell layers

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22
Q

What kind of stimulus are Pacinian corpuscles tuned to?

A

Vibration

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23
Q

Ruffini’s corpuscles are found (cutaneously/deep) in the skin

A

Deep

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24
Q

Other than skin, where are Ruffini’s corpuscles found?

A

Ligaments and tendons

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25
Q

What kind of stimulus are Ruffini’s corpuscles tuned to?

A

Stretch

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26
Q

Describe the positioning of Ruffini’s corpuscles relative to direction of stretch

A

Parallel to the direction of skin stretching

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27
Q

Where are Merkel’s disks localized in the skin?

A

Fingertips

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28
Q

Which kind of subcutaneous receptor would be the most useful for reading braille?

A

Merkel’s disks

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29
Q

What kinds of stimuli are Merkel’s disks tuned to? (2)

A

Light pressure
Shapes/edges/texture

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30
Q

Describe the anatomy of Merkel’s disks

A

Surrounded by supporting cells (Merkel’s cells) which release peptides to modulate the activation of the nerve terminal

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31
Q

Compared to other subcutaneous receptors, Merkel’s disks are (more/less) encapsulated

A

Less

32
Q

Describe lanceolate endings

A

Associated with hairy skin, specialized nerve endings which wrap around a hair follicle

33
Q

Which is likely more responsible for mechanosensation, the nerve fiber or the surrounding capsule cell?

A

Both are likely equally responsible

34
Q

True or false: free nerve endings act independently from other cells

A

False: receive input and have connections to multiple different cell types

35
Q

Free nerve endings are associated primarily with these kinds of cells

A

Keratinocytes

36
Q

What is the role of keratinocytes? (3)

A

Provide a water barrier (keep cells hydrated)
Secrete neuromodulatory factors (like ATP, which likely activates neurons)
Express TRP channels

37
Q

ATP released from keratinocytes binds to other keratinocytes via this receptor

A

P2Y2

38
Q

Activation of P2Y2 receptors induces… (2)

A

Release of calcium from internal calcium stores
Induces further release of ATP

39
Q

Where are muscle spindles located?

A

Within organs - primarily in muscle tissue

40
Q

What kind of sensory information do muscle spindles provide?

A

Stretch info within muscles, proprioception

41
Q

Which muscles have a lot of muscle spindles, why?

A

Extraocular muscles, muscles in head and neck have a lot of muscle spindles – Would be really painful to strain these muscles, could impact survival more heavily than straining a leg, for example

42
Q

Describe the very general pathway to the cortex from somatosensory receptors. What area of the cortex do these neurons terminate in?

A

Receptors > neurons > brainstem > thalamus > primary somatosensory cortex in the postcental gyrus of the parietal lobe

43
Q

All touch information goes to this area of the brain

A

Primary somatosensory cortex

44
Q

Which kind of neurons are associated with non-painful touch?

A

AB (A-beta)

45
Q

Which kinds of neurons are associated with pain? Which is the faster conducting fiber?

A

A-delta and C
A-delta conducts faster

46
Q

Describe the shapes of A-beta, A-delta and C fibers (size, myelination)

A

A-beta: Largest diameter, myelinated
A-delta: Medium dimeter, lightly myelinated
C: Small diameter, unmyelinated

47
Q

Why is 2-point discrimination the best on a human’s hands and face?

A

Because these are the areas of the body with the largest concentration of somatosensory receptors

48
Q

Where on the face are the largest amounts of somatosensory receptors?

A

Mouth

49
Q

The star appendages of the star-nosed mole are used exclusively for this mode of sensation

A

Touch (not used for smell)

50
Q

Describe the role of appendage #11 of the star-nosed mole

A

Used for fine discrimination, called the “tactile fovea”

51
Q

Each appendage of the star of a star-nosed mole is composed of 1000+ (1)

A

Eimer’s organs

52
Q

Describe Eimer’s organ

A

Merkel-like complexes which are highly sensitive to touch: shape/edges/texture

53
Q

Mechanosensory cells of the skin project to (1), which terminate in the (2) of the spinal cord

A
  1. A dorsal root ganglion
  2. Lateral ventral horns of the spinal cord
54
Q

Why are mechanotransduction channels thought to not use a second messenger cascade?

A

They respond so quickly that a 2nd messenger cascade is probably unlikely

55
Q

What are the 3 theories as to how mechanosensory channels open?

A
  1. Stretch of the membrane directly pulls a channel apart
  2. Receptors are tethered to the cytoskeleton or the ECM which when deformed could open the channel
  3. A movement-sensitive protein is associated with a channel, this could be tethered or directly sensitive to a channel inducing opening
56
Q

Which channel types are involved in mechanoreception? (3)

A

Epithelial sodium channels (ENaCs and ASICs)
TRP channels
Piezo channels

57
Q

ENaC channels are important for mechanosensation in this organism

A

Light touch in C. elegans

58
Q

Describe the changes in mechanoreception which occur in mice lacking ASIC receptors

A

Experience small changes in mechanosensitivity

59
Q

Which of the mechanosensitive channels is likely the most important for mechanosensation in mammals?

A

Piezo channels

60
Q

How could you investigate the mechanism for mechanosensation in drosophila without knowing which channels are involved?

A

Apply a mutagen to flies (creates random genomic mutations) and screen for flies which lack touch sensitivity

61
Q

What are the drosophila mechanosensory organs?

A

Johnston’s organ
Chordotonal organs
Bristles (act as external sense organs)

62
Q

Describe the proposed mechanism for bristle mechanosensation in flies

A

A bristle is connected to a neuron, which has a little neuron cap. When the bristle move, it makes contact with the cap, moves, and induces an action potential

63
Q

Chordotonal organs in flies detect this kind of motion

A

Stretch

64
Q

Flies which lacked mechanosensation usually had mutations in these genes

A

nompA-D

65
Q

One of the proteins which associates with the nompD genes in flies is (1). What does this mean?

A
  1. TRP channels

It means that TRP channels must be involved in mechanosensation in drosophila

66
Q

The external sense bristles on drosophila are connected to their underlying neurons (the dendritic caps of neurons) through…

A

Ankyrin repeats

67
Q

Describe how pulling on the ankyrin repeat of a bristle sense cell causes it to open

A

Ankyrin is probably tied to cation channels, when it moves it pulls the channel apart so it opens

68
Q

Describe the anatomy of a TRP channel

A

6TM, N=4

69
Q

What ions pass through TRP channels?

A

They are nonspecific cation channels

70
Q

What evidence suggests that TRP channels involved in drosophilia mechanotransduction are likely not using a 2nd messenger cascade?

A

They are activated too quickly: low latency of onset (200 us)

71
Q

If TRP channels don’t use a 2nd messenger, how do they initiate changes in the cell to open?

A

There is likely a direct coupling of mechanoreceptors to the TRP channel (e.g. like ankyrin repeats connecting to the cytoskeleton)

72
Q

Of the 2 kinds of Piezo channel (Piezo1 and Piezo2), which is the dominant transducer of mechanical forces for touch sensation in mice?

A

Piezo2

73
Q

What 2 pieces of evidence led us to believe that Piezo2 channels are the dominant mechanosensory channels in mammals?

A
  1. They are localized around subcutaneous nerve endings
  2. Piezo2 null mice have signficant touch defects
74
Q

Describe the movement to open Piezo2 channels

A

Trimer: rotate around the central pore (twisting back and forth motion like a camera shutter)

75
Q

What causes Piezo2 channels to open?

A

Movement of the cell membrane

76
Q

What are 3 locations in hairy skin where Piezo2 channels are found?

A

Merkel cell-neurite complexes
Lanceolate endings
Circumferential fibers

77
Q

What are 2 locations in glabrous skin where Piezo2 channels are located?

A

Merkel cell-neurite complexes
Meissner corpuscles

Biology 404 (14 decks)

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