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Flashcards in Peripheral sensory mechanisms Deck (41):
1

What type of skin covers the palms of the hands and the soles of the feet?

Glabrous skin

2

What is glabrous skin specialised for?

Somatosensation

3

How is glabrous skin specialised for somatosensation?

Skin ridges

Concentrated with receptors

4

Which broad class of receptors are found in glabrous skin?

Mechanorecptors

5

Which four types of mechanoreceptors are found in glabrous skin?

Meissner corpuscles

Merkel complexes

Ruffini organs

Pacinian corpuscles

6

Describe the location of the mechanoreceptors in the skin?

Meissner corpuscles and Merkel complexes are located close to the surface

Ruffini organs and Pacinian corpuscles are deeper

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7

Describe the axons that innervate the mechanoreceptors?

Large and myelinated

8

Where do the cell bodies of the axons that innervate mechanoreceptors lie?

In dorsal root ganglia

9

What are the endings of mechanorecepptors composed of?

Connective tissue

10

What are the connective tissue endings of each type of mechanoreceptor important for?

Determining the type of energy that the receptor will respond to

11

Which layers of the skin are the Ruffini and Pacinian corpuscles located in?

Ruffini corpuscles are located in the dermis

Pacinian corpuscles are located in the subcutaneous layer

12

What are the Ruffini and Pacinian corpuscles embedded in?

Connective tissue

13

Which receptors detect distortion of the skin?

Mechanoreceptors

14

What is the range of distortion detected by the mechanoreceptors?

10nm to sub-damaging distortion

15

What is the sensitivity and dynamic range of the mechanoreceptors to distortion of the skin?

0-1000 Hz

16

What is the receptove field of the mechanoreceptors that detect distortion of the skin?

10mm^2 to entire hand 

17

How do mechanoreceptors respond to mechanical distortion?

Mechanical distortion > Na channels opened by mechanical force > Na inflow > AP generated

18

Describe why radiating forces are important for mechanoreception?

Force applied to skin radiates > at some point, the mechanoreceptor will experience some of that force > generate AP if stimulus reaches threshold 

19

When will a mechanoreceptor generate an AP?

When the stimulus applied is strong enough to generate a large Na inflow that reaches threshold 

20

What happens if a stimulus does not cause Na to reach threshold?

No AP generated > we have no sensory experience of the event that is occurring 

21

Describe the difference between slowly adapting and rapidly adapting receptors?

SLOW: Show an initial bit of enthusiasm in response to a stimulus

Over time, encode the size of the stimulus

RAPID: Short initial excitement

After that, only respond when there is a change in stimulus 

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22

Does the nervous system generally act like slowly adapting or rapidly adapting receptors?

Rapidly adapting

23

Which of the mechanoreceptors are slowly adapting? Which are rapidly adapting?

Slowly adapting: Merkel complexes and Ruffini organs 

Rapidly adapting: Meissner corpuscles and Pacinian corpuscles 

24

Where are Merkel complexes and Meissner corpuscles located?

Merkel complexes are located at the tips of epidermal ridges 

Meissner complexes are found near the skin surface

25

Which particular stimuli do each of the four mechanoreceptors respond to?

Merkel: indentation 

Meissner: transient response to skin movement

Ruffini: sustained response to skin movement

Pacinian: transient response to vibration

26

What types of connections do the axons of mechanoreceptors have in the spinal cord?

Local connections and ascending projections to the brain

27

Describe the difference in firing rate between tactile and nociceptive primary sensory afferents?

Tactile: don't change firing rate with increased force

Nociceptive: increased firing rate with increased stimulus, as well as increased firing once stimulus is removed 

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28

Describe the receptive fields of each of the four types of mechanorecptor?

Merkel: small, high density

Meissner: small, high density

Ruffini: large, low density

Pacinian: large, low density

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29

Why are all four mechanorecpetors required?

To build a profile of information and make judgements about what we are touching/feeling

30

When performing a simple manipulation task, what do each of the four mechanoreceptors encode?

Meissner: rate of force

Merkel: grip force

Pacinian: vibrations

Ruffini: hand posture

31

How does firing from each of the four mechanoreceptors change throughout a simple manipulation task?

Meissner and Pacinian have bursts of activity when there is change (rapidly adapting)

Merkel and Ruffini provide sustained information (slowly adapting)

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32

What are the mechanoreceptors located in muscles called?

Muscle spindles

33

What does the two-point discrimination threshold describe?

Measures how much territory a single receptor is responsive to

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34

Why does the two-point discrimination threshold vary across the body?

Size of receptive fields varies across the body 

Small receptive fileds > can discriminate well

35

How does two-point discrimation vary between areas with large receptive fields and areas with small receptive fields?

Large receptive fields > hard to discriminate between two points

Small receptove fields > easier to discriminate between two points

 

36

What is the conduction velocity of the mechanoreceptors?

35-75 m/s

Fast

37

What is the axon diameter of the mechanoreceptors?

6-12 um

Large

38

Why are dermatomal patterns different to spinal nerve distribution?

Presence of anastamoses

39

Describe the endings of nociceptors?

Free nerve endings

40

How does the spinal cord arrangement differ for mechanoreceptors and nociceptors?

Mechanoreceptors have an ipislateral arrangement

Nociceptors have a contralateral arrangement 

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41

Describe the spinal cord connections of nocicpetors?

Make their most significant connections in the spinal cord at the level that they enter