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

2/8: Thermal Sensation and Nociception I Flashcards

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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
What is vanilloid receptor activated by?
Capsaicin, high temperatures, and protons (hot peppers are hot depending on how much capsaicin)
26
What does vanilloid receptor decrease?
The threshold of channel activation so that heat is perceived at 33*C
27
What are the receptors for cold-menthol receptor type I?
CMR1 (cold menthol receptor)/TRPM8
28
What are cold-menthol receptor type I associated with?
Menthol and related compounds
29
What does cold-menthol receptor type I decrease?
The threshold of the channels so that warmer compounds are perceived as cold
30
What kind of receptive fields do thermoreceptors in the orofacial region have?
Small
31
What kind of receptive fields do nociceptive thermal receptors have?
Large receptive fields
32
Does the mouth have more cool or warm receptors?
More cool than warm BUT, whole mouth studies indicate that subjects are better able to accurately detect increments of warming rather than cooling
33
What is the face more sensitive to?
The face is 2-4 times as sensitive to thermal change (warming) as the inner mucosa
34
What are thermoreceptors in tongue most sensitive to?
Changes in temperature
35
What does activation of nociceptors result in the perception of?
PAIN, an unpleasant & emotional experience associated with actual or potential tissue damage
36
All nociception produces ______, though not all ______ results from nociception
Pain; pain
37
Unlike most sensory modalities, _______ can be evoked by any stimuli (mechanical, thermal or chemical) if it is strong enough
Pain
38
Why do we sense pain?
So the body can detect, localize, and limit tissue damage
39
What is acute pain?
Physiologic pain; <6 months duration
40
What are the two types of acute pain?
1. Somatic 2. Visceral
41
Where is somatic pain located?
Skin, subcutaneous tissues or mucus membranes (superficial) or muscles, tendons, joints or bones (deep)
42
What is superifical somatic pain?
Localized, sharp, pricking and burning
43
What is deep somatic pain?
Dull, aching, diffuse, and can be referred
44
What is visceral pain due to?
A disease process or abnormal function involving an internal organ (visceral) or its covering (parietal)
45
What is true visceral pain?
Dull, diffuse, poorly localized and associated with nausea and auronomic symptoms
46
What is parietal visceral pain?
Sharp, stabbing and better localized than true pain
47
Both somatic and visceral pain can be...
Referred
48
Referred pain most frequently occurs with pain of _________ origin
Visceral (& sometimes parietal)
49
Where do the two nociceptic afferent neurons from different regions of the body converge?
Same second order neuron - the brain doesn't know which is the true source of input and may make a mistake in interpretation
50
What is chronic pain?
Occurs beyond the usual course of an acute disease or after a reasonable time to healing to occur
51
What are three types of chronic pain?
1. Nociceptive 2. Neuropathic 3. Mixed pain
52
What is nociceptive pain due to?
Activation of nociceptors
53
What is neuropathic pain due to?
Neuronal injury
54
Describe neuropathic pain
Paroxysmal, sharp and stabbing
55
What is neuropathic pain associated with?
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
Autonomic responses are only a part of _______ pain
Acute
57
Moderate to severe pain can affect function of every organ AND adversely influence postoperative _______&_________
Morbidity & mortality - poor pain control will worsen patient outcomes
58
Where are nociceptors found?
On free nerve endings
59
What 3 things are nociceptors sensitive to?
1. Mechanical stimuli 2. Thermal stimuli 3. Chemical stimuli
60
What are chemicals known to excite nociceptors?
Substance P, ATP, calcitonin gene related peptide (CGRP), glutamate, aspartate, Bradykinin, potassium, Histamine, serotonin
61
What chemicals known to sensitize nociceptors?
Substance P, Prostaglandins, Histamine, Bradykinin
62
What chemicals are known to inhibit nociceptors?
Enkephalins, β Endorphin, Cannabinoids
63
What chemical sensitizes and excites nociceptors?
Substance P
64
What is summation of nociception based on?
Spatial - based on # of receptors activated
65
Minimal adaptation anda. nociceptors activity _______ if the painful stimuli continues (hyperalgesia) due to nociceptor ___________
INCREASES; sensitization
66
What is allodynia?
Painful sensation to a innocuous stimulus
67
What can stimulation of nociceptors also lead to?
antidromal (reverse) activation of nociceptive nerve terminals and release of substance P and calcitonin gene related peptide
68
What does release of substance P and calcitonin gene related peptide cause?
mast cell degranulation, vasodilation and edema, and further sensitization and activation of nociceptors (neurogenic inflammation)
69
What is the triple response?
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
What fibers are small and myelinated?
Alpha delta fibers
71
What neurotransmitters are included in alpha delta fibers?
Glutamate
72
What pain is associated with alpha delta fibers?
Sharp, localized pain (FAST PAIN)
73
What stimuli influences alpha dental fibers?
Thermal and mechanical stimuli
74
What fibers are unmyelinated?
C fibers
75
What neurotransmitters are included in C fibers?
Substance P
76
What pain is associated with C fibers?
Dull, diffuse pain (SLOW PAIN)
77
What stimuli are associated with C fibers?
Thermal, mechanical and chemical stimuli
78
Where does the second order neuron cross over?
In the anterior commissure to the opposite side of the spinal cord to ascend contralaterally
79
What is the major pain pathway in the CNS?
The lateral spinothalamic tract
80
What are the two parts of the lateral spinothalamic tract?
Neospinothalmic Paleospinothalamic
81
What fibers is the neospinothalmic pathway made of?
A delta fibers
82
What does the neospinothalmic pathway provide?
Location, intensity and duration information
83
What fibers make up the paleospinothalamic tract?
Mostly C fibers
84
What do paleospinothalamic fibers synapse with?
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
What are the alternate pathways for the pain pathway in the CNS?
i. Spinoreticular pathway. Mediates arousal & autonomic responses ii. Spinomesencephalic pathway. Activates anti- nociceptive, descending pathways iii. Spinohypothalamic pathway
86
In the lateral spinothalamic pathway, where is the cell body in the first order neuron?
ell body in dorsal root ganglion (or somatic afferent ganglion of cranial nerves)
87
In the lateral spinothalamic pathway, where is the cell body in the second order neuron?
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
In the lateral spinothalamic pathway, where is the cell body in the third order neuron?
Cell body in thalamus, axons project to the sensory cortex. Sensory Homunculus
89
What are the two ways that second-order neurons are in the dorsal horn?
1. Nociceptive-specific Neurons 2. Wide Dynamic Range (WDR) Neurons
90
Nociceptive-specific neurons receive only _______ stimuli
Noxious
91
WDR neurons receive ____________ input from ____,____,and ____ fibers
Non-noxious afferent; alpha beta; alpha delta; and C fibers
92
What neurons are the most prevalent in the dorsal horn?
WDR (wide dynamic range) neuron (most abundant in lamina V)
93
Where do first and second order neurons synapse?
In the dorsal horn of the spinal cord
94
During repeated stimulation, describe WDR diring rate?
WDR neurons characteristically increase their firing rate exponentially (wind-up), even with the same stimulus intensity.
95
Do WDR neurons or nociceptive specific neurons have a larger receptive field?
WDR
96
Where are nociceptive specific neurons found?
In lamina I and have discrete, somatic receptive fields
97
What do nociceptive specific neurons respond to?
they are normally silent and respond only to high- threshold noxious stimulation, poorly encoding stimulus intensity

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