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D1 Spring - Physiology > 2/8: Thermal Sensation and Nociception I > Flashcards

2/8: Thermal Sensation and Nociception I Flashcards

1
Q

Where are thermal receptors (thermoreceptors) found on?

A

Free nerve endings and in the skin
Also- hypothalamus, spinal cord, and deep tissues

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2
Q

What are the sensitivities of temperature sensation categorized by?

A

Cool and warm

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3
Q

How many cool vs warm receptors?

A

3-10 times as many cool receptors at any skin surface

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4
Q

What are nociceptors activated by?

A

Extreme cold or heat

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5
Q

Which do you perceive first- a thermal or mechanical sensation?

A

Mechanical because use beta fibers which are myelinated and have larger diameter

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6
Q

What are warm signals transmitted by?

A

Mainly C
and Alpha delta fibers

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7
Q

What are cool signals transmitted by?

A

Mainly Alpha delta
and C fibers

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8
Q

Mechanism of thermal sensation are most likely achieved by sensing?

A

A change in metabolic rate

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9
Q

What increases the rate of intracellular chemical reacitons?

A

Temperature

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10
Q

Transient Receptor Potential (TRP) channels are identified and each are sensitive to what?

A

A different temperature range
Some chemicals (capsaicin, menthol) elicit thermal sensations, too

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11
Q

What is temperature perception based on?

A

Activation of a combination of the receptors

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12
Q

What are examples of cold pain?

A

Tickling
Pricking
Aching
Burning
numbing

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13
Q

What are examples of hot pain?

A

Sharp
Pricking
Stinging
Burning
Throbbing

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14
Q

If skin reaches freezing, __________ fibers are no longer stimulated?

A

Cold/pain

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15
Q

What kind of fibers are activated at higher temperatures?

A

Heat/pain fibers
Sometimes cold fibers are activated too, paradoxical cold (when cold fibers are activated at warm temps)

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16
Q

What do thermoreceptors adapt to?

A

They mostly (but never completely) adapt to constant temperature; BUT
they quickly change their activity in response to changes in temperature

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17
Q

What are thermoreceptors very sensitive to?

A

Changes in temperature

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18
Q

If temperature reaches one of the pain thresholds, what happens to the sensation?

A

Becomes more persistent throughout the stimulus

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19
Q

What are warm and cool receptors best able to detect?

A

A change at the mid-range of their temperature sensitivity (that is where they are most sensitive)

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20
Q

What happens if nociceptors are simultaneously activated?

A

The system is even better to discern small changes in temp

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21
Q

As temperature increases (or decreases) within a
range of a thermoreceptor’s sensitivity, more and
more receptors are _________

A

Activated, based on their varying thresholds
Thus, perception is increased
There is also an increase in the rate that thermal
receptors fire (but not nociceptors)

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22
Q

The greater the area of skin affected by a thermal stimulus, the greater the number of ________, __________, and __________ activated, and thus the _____________ the perceived sensation

A

Receptors; receptive fields; first order neurons; greater
- There is a much greater ability for detection of a
temperature stimulus if a large region is activated

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23
Q

Receptors in the oral cavity are primarily sensitive to?

A

Temperature, but certain receptors are also sensitive to chemicals

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24
Q

What is the receptor for vanilloid receptor?

A

TRPV1 receptor

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25
Q

What is vanilloid receptor activated by?

A

Capsaicin, high temperatures, and protons (hot peppers are hot depending on how much capsaicin)

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26
Q

What does vanilloid receptor decrease?

A

The threshold of channel activation so that heat is perceived at 33*C

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27
Q

What are the receptors for cold-menthol receptor type I?

A

CMR1 (cold menthol receptor)/TRPM8

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28
Q

What are cold-menthol receptor type I associated with?

A

Menthol and related compounds

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29
Q

What does cold-menthol receptor type I decrease?

A

The threshold of the channels so that warmer compounds are perceived as cold

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30
Q

What kind of receptive fields do thermoreceptors in the orofacial region have?

A

Small

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31
Q

What kind of receptive fields do nociceptive thermal receptors have?

A

Large receptive fields

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32
Q

Does the mouth have more cool or warm receptors?

A

More cool than warm
BUT, whole mouth studies indicate that subjects are
better able to accurately detect increments of
warming rather than cooling

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33
Q

What is the face more sensitive to?

A

The face is 2-4 times as sensitive to thermal change
(warming) as the inner mucosa

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34
Q

What are thermoreceptors in tongue most sensitive to?

A

Changes in temperature

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35
Q

What does activation of nociceptors result in the perception of?

A

PAIN, an unpleasant & emotional experience
associated with actual or potential tissue damage

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36
Q

All nociception produces ______, though not all ______ results from nociception

A

Pain; pain

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37
Q

Unlike most sensory modalities, _______ can be evoked by any stimuli (mechanical, thermal or chemical) if it is strong enough

A

Pain

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38
Q

Why do we sense pain?

A

So the body can detect, localize, and limit tissue damage

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39
Q

What is acute pain?

A

Physiologic pain; <6 months duration

40
Q

What are the two types of acute pain?

A
  1. Somatic
  2. Visceral
41
Q

Where is somatic pain located?

A

Skin, subcutaneous tissues or mucus membranes (superficial) or muscles, tendons, joints or bones (deep)

42
Q

What is superifical somatic pain?

A

Localized, sharp, pricking and burning

43
Q

What is deep somatic pain?

A

Dull, aching, diffuse, and can be referred

44
Q

What is visceral pain due to?

A

A disease process or abnormal function involving an internal organ (visceral) or its covering (parietal)

45
Q

What is true visceral pain?

A

Dull, diffuse, poorly localized and associated with nausea and auronomic symptoms

46
Q

What is parietal visceral pain?

A

Sharp, stabbing and better localized than true pain

47
Q

Both somatic and visceral pain can be…

A

Referred

48
Q

Referred pain most frequently occurs with pain of _________ origin

A

Visceral (& sometimes parietal)

49
Q

Where do the two nociceptic afferent neurons from different regions of the body converge?

A

Same second order neuron
- the brain doesn’t know which is the true source of input and may make a mistake in interpretation

50
Q

What is chronic pain?

A

Occurs beyond the usual course of an acute disease or after a reasonable time to healing to occur

51
Q

What are three types of chronic pain?

A
  1. Nociceptive
  2. Neuropathic
  3. Mixed pain
52
Q

What is nociceptive pain due to?

A

Activation of nociceptors

53
Q

What is neuropathic pain due to?

A

Neuronal injury

54
Q

Describe neuropathic pain

A

Paroxysmal, sharp and stabbing

55
Q

What is neuropathic pain associated with?

A

Hyperalgesia (increased sensitivty to pain)
“Neuropathic pain includes pain associated with diabetic neuropathy,
causalgia, phantom limbs, postherpetic neuralgia, stroke, spinal cord injury,
and multiple sclerosis. Cancer pain and chronic low back pain may have
prominent neuropathic components.”

56
Q

Autonomic responses are only a part of _______ pain

A

Acute

57
Q

Moderate to severe pain can affect function of every organ AND adversely influence postoperative _______&_________

A

Morbidity & mortality
- poor pain control will worsen patient outcomes

58
Q

Where are nociceptors found?

A

On free nerve endings

59
Q

What 3 things are nociceptors sensitive to?

A
  1. Mechanical stimuli
  2. Thermal stimuli
  3. Chemical stimuli
60
Q

What are chemicals known to excite nociceptors?

A

Substance P, ATP,
calcitonin gene related peptide (CGRP), glutamate, aspartate, Bradykinin, potassium, Histamine, serotonin

61
Q

What chemicals known to sensitize nociceptors?

A

Substance P, Prostaglandins, Histamine, Bradykinin

62
Q

What chemicals are known to inhibit nociceptors?

A

Enkephalins, β
Endorphin, Cannabinoids

63
Q

What chemical sensitizes and excites nociceptors?

A

Substance P

64
Q

What is summation of nociception based on?

A

Spatial
- based on # of receptors activated

65
Q

Minimal adaptation anda. nociceptors activity _______ if the painful stimuli continues (hyperalgesia) due to nociceptor ___________

A

INCREASES; sensitization

66
Q

What is allodynia?

A

Painful sensation to a innocuous stimulus

67
Q

What can stimulation of nociceptors also lead to?

A

antidromal (reverse) activation of nociceptive nerve terminals and release of substance P and calcitonin gene related peptide

68
Q

What does release of substance P and calcitonin gene related peptide cause?

A

mast cell degranulation, vasodilation and edema,
and further sensitization and activation of nociceptors (neurogenic
inflammation)

69
Q

What is the triple response?

A
  1. Red flush around site of
    injury (flare)
  2. Local tissue edema
  3. Sensitization to noxious
    stimuli
    - Tissue injury leads to local release of endogenous inflammatory mediators (ex.
    Histamine, Prostaglandins, Bradykinin, etc.) that excite or sensitize nociceptors causing hyperalgesia
70
Q

What fibers are small and myelinated?

A

Alpha delta fibers

71
Q

What neurotransmitters are included in alpha delta fibers?

A

Glutamate

72
Q

What pain is associated with alpha delta fibers?

A

Sharp, localized pain (FAST PAIN)

73
Q

What stimuli influences alpha dental fibers?

A

Thermal and mechanical stimuli

74
Q

What fibers are unmyelinated?

A

C fibers

75
Q

What neurotransmitters are included in C fibers?

A

Substance P

76
Q

What pain is associated with C fibers?

A

Dull, diffuse pain (SLOW PAIN)

77
Q

What stimuli are associated with C fibers?

A

Thermal, mechanical and chemical stimuli

78
Q

Where does the second order neuron cross over?

A

In the anterior commissure to the opposite side of the spinal cord to ascend contralaterally

79
Q

What is the major pain pathway in the CNS?

A

The lateral spinothalamic tract

80
Q

What are the two parts of the lateral spinothalamic tract?

A

Neospinothalmic
Paleospinothalamic

81
Q

What fibers is the neospinothalmic pathway made of?

A

A delta fibers

82
Q

What does the neospinothalmic pathway provide?

A

Location, intensity and duration information

83
Q

What fibers make up the paleospinothalamic tract?

A

Mostly C fibers

84
Q

What do paleospinothalamic fibers synapse with?

A

Brainstem structures (reticular formation, Periaqueductal Gray Region, Limbic System, Hypothalamus) and also with diffuse areas of the cortex for poorly localized sense of pain

85
Q

What are the alternate pathways for the pain pathway in the CNS?

A

i. Spinoreticular pathway.
Mediates arousal &
autonomic responses
ii. Spinomesencephalic
pathway. Activates anti-
nociceptive, descending
pathways
iii. Spinohypothalamic pathway

86
Q

In the lateral spinothalamic pathway, where is the cell body in the first order neuron?

A

ell body in dorsal root ganglion (or somatic afferent ganglion of cranial nerves)

87
Q

In the lateral spinothalamic pathway, where is the cell body in the second order neuron?

A

cell body is in dorsal nuclei & axons decussate via the anterior commissure and
terminate in thalamus. Can be solely nociceptive OR
Wide-Dynamic Range (WDR) neurons

88
Q

In the lateral spinothalamic pathway, where is the cell body in the third order neuron?

A

Cell body in thalamus, axons
project to the sensory cortex. Sensory Homunculus

89
Q

What are the two ways that second-order neurons are in the dorsal horn?

A
  1. Nociceptive-specific
    Neurons
  2. Wide Dynamic Range (WDR) Neurons
90
Q

Nociceptive-specific neurons receive only _______ stimuli

A

Noxious

91
Q

WDR neurons receive ____________ input from ____,____,and ____ fibers

A

Non-noxious afferent; alpha beta; alpha delta; and C fibers

92
Q

What neurons are the most prevalent in the dorsal horn?

A

WDR (wide dynamic range) neuron (most abundant in lamina V)

93
Q

Where do first and second order neurons synapse?

A

In the dorsal horn of the spinal cord

94
Q

During repeated stimulation, describe WDR diring rate?

A

WDR neurons characteristically
increase their firing rate
exponentially (wind-up), even with the same stimulus
intensity.

95
Q

Do WDR neurons or nociceptive specific neurons have a larger receptive field?

A

WDR

96
Q

Where are nociceptive specific neurons found?

A

In lamina I and have discrete, somatic receptive fields

97
Q

What do nociceptive specific neurons respond to?

A

they are normally silent
and respond only to high-
threshold noxious stimulation, poorly encoding stimulus intensity

D1 Spring - Physiology (17 decks)

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