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NAB > 6a. Cutaneous Receptors > Flashcards

6a. Cutaneous Receptors Flashcards

1
Q

Accessory Structures

- 5 Functions

A
  • Protection
  • Conduction
  • Concentration
  • Analysis
  • Sensitisation or inhibition
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2
Q

Cutaneous Receptors

- 2 Types

A
  • Encapsulated nerve endings

- Non-encapsulated nerve endings

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3
Q

Encapsulated Nerve Endings

- 4 Types

A

Slowly adapting type I afferents:
- Merkel cells

Slowly adapting type II afferents:
- Ruffini endings

Rapidly adapting type I afferents:
- Meissner’s corpuscles

Rapidly adapting type II afferents:
- Pacinian corpuscles

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4
Q

Mechanotransduction

- 3 Theories

A

Ion channels are opened by:

  1. Changes in lipid tension
  2. Movement of structural proteins linked to the channel
  3. Structural protein linked by a 2nd messenger cascade
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5
Q

Temporal Discharge Patterns

A

Rapidly adapting receptors only generate action potentials at the onset of the stimulus.

Slowly adapting receptors produce tonic action potential discharge in response to a steady stimulus.

Provides stimulus frequency information.

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6
Q

Phase-Locking

A

Provides stimulus frequency information

Rapidly adapting receptor gives a single action potential for each [phase of the sinusoid stimulus, treating each period of the waveform as a new stimulus

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7
Q

Fibre Recruitment

A

Provides stimulus intensity information

Number of active fibres is linearly related to amplitude of sinusoid stimulus

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8
Q

Meissner’s Corpuscles

- Receptor Type

A

Rapidly adapting type I afferent

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9
Q

Meissner’s Corpuscles

- Number

A

150 per cm2 glamorous skin

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10
Q

Meissner’s Corpuscles

- Afferent fibres

A

20 Meissner’s corpuscles per afferent

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11
Q

Meissner’s Corpuscles

- Structure

A

Directly connected to epidermal cells and collagen fibres

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12
Q

Meissner’s Corpuscles

- Receptive field

A

Small

2-5mm diameter

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13
Q

Meissner’s Corpuscles

- Stimulus Type

A

Respond best to low frequency vibration 10-40Hz

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14
Q

Meissner’s Corpuscles

- Function

A

Fine touch

Perception of slip between the skin and an object, to feedback on grip control

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15
Q

Pacinian Corpuscles

- Receptor Type

A

Rapidly adapting type II afferent

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16
Q

Pacinian Corpuscles

- Number

A

350 per finger

850 per palm

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17
Q

Pacinian Corpuscles

- Afferent Fibres

A

1 Pacinian corpuscles per afferent fibre

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18
Q

Pacinian Corpuscles

- Structure

A

Central nerve ending surrounded by concentric layers of cellular membrane called lamellae, alternating with fluid filled spaces

Enclosed in a capsule

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19
Q

Pacinian Corpuscles

- Receptive Field

A

Large

Central zone of maximal sensitivity surrounded by a large continuous surface of the finger or palm

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20
Q

Pacinian Corpuscles

- Stimulus Type

A

Extremely sensitive

Respond to 10nm of skin motion at 200Hz

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21
Q

Pacinian Corpuscles

- Function

A

Perception of events through an object held in the hand

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22
Q

Pacinian Corpuscles

- Location

A

Widely distributed

  • Hypodermis and epidermis of glaborous skin
  • Connective tissue in muscles
  • Between tendons
  • Close to bone periosteum
  • Mesentery in cats
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23
Q

Pacinian Corpuscles

- Lamellae Removal

A

Prevents rapid adaptation to sustained stimulus.

Stimulus-induced receptor potential persists until the stimulus is removed

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24
Q

Vibration Detection

- Cutaneous Receptors Responsible

A
  • Meissner’s corpuscles

- Pacinian corpuscles

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25
Q

Vibration Detection

- Experiment

A

Local anaesthetic applied to the skin:
- Reduces effectiveness of the more superficial Meissner’s corpuscles

Pre-Adaptation:

  • 250Hz preadaptation reduces the effectiveness of the Pacinian corpuscle as they adapt
  • 30Hz preadaptation reduces the effectiveness of the Meissner’s corpuscle as they adapt
26
Q

Merkel Cells

- Receptor Type

A

Type I slowly adapting afferent

27
Q

Merkel Cells

- Location

A

Just below the crests of fingerprint ridges

28
Q

Merkel Cells

- Afferent Fibres

A

20 Merkel cells per afferent fibre

29
Q

Merkel Cells

- Receptive Field

A

Small

30
Q

Merkel Cells

- Stimulus Type

A

Linear response to indentation up to 1500micrometers

10x more sensitive to dynamic stimuli

31
Q

Ruffini Endings

- Receptor Type

A

Type II slowly adapting afferent

32
Q

Ruffini Endings

- Afferent Fibres

A

1 Ruffini ending per afferent fibre

33
Q

Ruffini Endings

- Stimulus Type

A

Stretch

Perception of object motion and providing information about hand shape and finer position

34
Q

Ruffini Endings

- Location

A

Deep

35
Q

Braille

- Receptor Type

A

Slowly adapting type I afferents (Merkel)

36
Q

Receptive Field

- Definition

A

The spatial domain where stimulation excites or inhibits the afferent neurone.

Receptive field size determines tactile acuity, where smaller receptive fields give greater tactile acuity

37
Q

Receptive Field

- Measuring

A

Microneurography

Metal recording electrode is placed through the skin into the median nerve and stimulating areas of the sand determines which areas could be excited to give and increase in neural activity

38
Q

Type I Afferent Mechanoreceptors

A

Small receptive field

High density

39
Q

Type II Afferent Mechanoreceptors

A

Large receptive field

Low density

40
Q

2 Point Limen

A

Way to determine the tactical acuity of different body parts

Smallest discriminable distance between 2 points of contact

Acuity tends to increase with an increase in mobility of body parts, in the upper body at least

41
Q

Non-Encapsulated Nerve Endings

- 2 Types

A
  • Nociceptors

- Thermoreceptors

42
Q

Thermoreceptors

- Cold and Warm Spots

A

The number of cold spots greatly exceeds the number of warm spots

there are more receptors than there are cold and warm spots, and require simultaneous activation to give sensation due to spatial summation

43
Q

Thermoreceptors

- Types

A
  • TRPV4
  • TRPV1
  • TRPV2
  • TRPM8
  • TRPA1
44
Q

Thermoreceptors

- TRPV4

A

Activated by temperatures >36

45
Q

Thermoreceptors

- TRPV1

A

Activated by:

  • Capsaicin
  • Painful increases in temperature >43
46
Q

Thermoreceptors

- TRPV2

A

Activated by painful increases in temperature >52 which signal damage to the flesh

47
Q

Thermoreceptors

- TRPM8

A

Activated by:

  • Non-painful decreases in temperature <25
  • Methanol
  • Methol
48
Q

Thermoreceptors

- TRPA1

A

Activated by:

  • Painful cold
  • Mustard, horseraddish and wasabi
49
Q

Cold Receptor Afferents

A

α-delta and C-fibres

50
Q

Warm Receptor Afferents

A

Sub-population of C-fibres

51
Q

Paradoxical Cold

A

Heat stimulus is applied to a cold spot, gives cold sensation, as opposed to painful heat sensation that would occur if it was applied to a diffuse area of skin.

Activity in the cold fibre is experiences as cold irrespective of the physical nature of the stimulus
- Labelled line coding

52
Q

Nociceptors

- Structure

A

Free nerve endings, making them very sensitive to chemicals produced or released at the site of injury

53
Q

Nociceptors

- Pain Phases

A
  1. Transient sharp
  2. Dull burning

2 phase sensation suggests 2 nociceptors

54
Q

Nociceptors

- 2 Types

A
  • A-delta fibres = transient sharp pain

- C fibres = Dull burning pain

55
Q

Nociceptors

- A-Delta Fibres

A

Transient sharp pain

Myelinated to facilitate rapid response

56
Q

Nociceptors

- C Fibres

A

Dull burning pain

Un-myelinated

Poly-modal, responding to:

  • Temperature <15 and >43
  • Strong mechanical stimuli
  • Chemical stimuli
57
Q

Pleasant Touch of Hairy Skin

- Fibre Type

A

C fibre tactile afferents (CT)

Slow conduction velocity 1m/s

58
Q

Pleasant Touch of Hairy Skin

- Discovery

A

Microneurography

59
Q

Pleasant Touch of Hairy Skin

- Stroke Velocity vs Pleasantness

A

Positive correlation

- Suggests these afferents are more concerned with emotional feeling than touch

60
Q

Sensitisation and Desensitisation

A

Mechanoreceptors desensitise to constant stimulation

Nociceptors sensitise to constant stimulation

61
Q

Acute Sensory Neuropathy Syndrome

A

Rare

Loss of cutaneous sensation and proprioception

62
Q

Astereognosia

A

Inability to identify objects from touch

Can occur in some patients suffering from multiple sclerosis

NAB (37 decks)

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