Pain and Temperature Sensations Flashcards

1
Q

Core Body Temperature

A

37⁰ C

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2
Q

Body temperature has a

circadian fluctuation of

A
  1. 5-

0. 7°C (1-1.5° F)

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3
Q

Temperature is lowest at

—, highest in the —

A

6:00am

evening

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4
Q

Temperature regulation is less

precise in

A

young children;
normally have a temperature
that is 0.5°C or so above adults.

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5
Q

Thermal Receptors (thermoreceptors) are on

A

free nerve endings
& commonly found in the skin. Also in hypothalamus, spinal cord,
& deep tissues.

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6
Q

Categorized by their different sensitivities: (2)

A

cool

warm

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7
Q

Cool and warm receptors innervate

A

discrete regions of skin

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8
Q

There are – times as many cool receptors at any skin surface

A

3-10

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9
Q

— are activated by extreme cold or heat

A

Nociceptors

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10
Q
Which do you 
perceive first-   
a thermal or 
mechanical 
sensation?
A

mechanical

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11
Q

After thermoreceptors are activated,
Warm signals are transmitted by:
Cool signals are transmitted by:

A

C and Aδ fibers

Aδ and C fibers

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12
Q

The mechanism of thermal sensation is most likely achieved by
sensing a change in

A

metabolic rate

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13
Q

— increases the rate of intracellular chemical

reactions

A

Temperature

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14
Q

Several Transient Receptor Potential (TRP) channels

have been identified, each sensitive to a different

A

temperature range. Some chemicals (Capsaicin, Menthol)

elicit thermal sensations, too.

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15
Q

Temperature Perception

Based on the Activation of a

A

Combination of the Receptors

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16
Q

COLD PAIN: (5)

A
Tickling, 
Pricking, 
Aching, 
Burning, 
Numbing
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17
Q

HOT PAIN: (5)

A
Sharp, 
Pricking, 
Stinging, 
Burning, 
Throbbing
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18
Q

If skin reaches —, cold/pain fibers are no longer stimulated.

A

freezing

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19
Q

At ~ –°C, heat/pain fibers are activated.

Sometimes cold fibers are activated, too—

A

45

paradoxical cold

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20
Q

Average skin

temperature =

A

34-35ºC;
equal activation of cool
and warm receptors.

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21
Q
Adaptation of Thermoreceptors
• They mostly (but never completely) 
adapt to --- ---; BUT 
they quickly change their activity in 
response to ---
A

constant temperature
changes in temperature.
They are very sensitive to changes
in temperature.

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22
Q

Adaptation of Thermoreceptors
• If the temperature reaches one of the
pain thresholds, the sensation
becomes

A

more persistent throughout

the stimulus

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23
Q

Sensitivity of Thermoreceptors
• Warm and Cool receptors are best able to detect a change at the
— of their temperature sensitivity (that is where they are
most sensitive)

A

mid-range

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24
Q

Sensitivity of Thermoreceptors
• If nociceptors are simultaneously activated, the system is even
better able to

A

discern small changes in temperature

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25
As temperature increases (or decreases) within a range of a thermoreceptor’s sensitivity,
more and more receptors are activated, based on their varying thresholds. Thus perception is increased.
26
There is also an increase in the rate that --- receptors fire (but not nociceptors)
thermal
27
The greater the area of skin affected by a thermal stimulus, the greater the
number of receptors, receptive fields, and first order neurons activated and thus the greater the perceived sensation.
28
There is a much greater ability for detection of a --- stimulus if a large region is activated.
temperature
29
Receptors are primarily sensitive to ---, but certain | receptors are also sensitive to ---
temperature | chemicals
30
Vanilloid Receptor Subtype (3)
1. TRPV1 Receptor 2. Activated by capsaicin, temperature >43°C, and protons 3. Decreases the threshold of channel activation so that heat is perceived at 33°C.
31
Cold-Menthol Receptor Type I (CMR1/TRPM8) (2)
1. Menthol and related compounds 2. Decreases the threshold of the channels so that warmer compounds are perceived as cold.
32
Characteristics of Thermoreceptors in Orofacial Region | receptive field size:
Small receptive fields (nociceptive thermal receptors | have large receptive fields)
33
Characteristics of Thermoreceptors in Orofacial Region | warm vs cool
More cool than warm receptors BUT, whole mouth studies indicate that subjects are better able to accurately detect increments of warming rather than cooling
34
Characteristics of Thermoreceptors in Orofacial Region | the face vs inner mucosa
The face is 2-4 times as sensitive to thermal change | (warming) as the inner mucosa
35
Characteristics of Thermoreceptors in Orofacial Region Thermoreceptors in --- are the most sensitive to changes in temperature.
tongue
36
Due to activation of nociceptors. This usually results in the perception of
PAIN, an unpleasant & emotional experience | associated with actual or potential tissue damage.
37
nociception and pain relationship
All nociception produces pain, though not all pain | results from nociception.
38
Unlike most sensory modalities, pain can be evoked | by
``` any stimuli (mechanical, thermal or chemical) if it is strong enough. ```
39
We sense pain so that the body can (3)
detect, localize, and limit tissue damage.
40
PAIN, whatever its cause, is never ---. Pain is the | most common reason patients (2)
benign | seek healthcare AND the most common symptom of disease.
41
types of acute pain (2)
somatic | visceral
42
acute pain
Physiologic Pain; <6 months duration
43
Somatic:
From skin, subcutanous tissues or mucus membranes (Superficial) or muscles, tendons, joints or bones (Deep). – Superficial Somatic: localized, sharp, pricking and burning – Deep Somatic: dull, aching, diffuse and can be referred
44
Visceral:
Due to a disease process or abnormal function involving an internal organ (Visceral) or its covering (Parietal). – True Visceral: dull, diffuse, poorly localized and associated with nausea and autonomic symptoms. – Parietal Visceral: sharp, stabbing and better localized than true pain.
45
Both types of visceral pain can be --
referred
46
Referred pain most frequently occurs with pain of | --- Origin
visceral (& sometimes parietal)
47
Two nociceptive afferent neurons—from different regions of the body—converge on the same second order neuron. The brain doesn’t know which is the true source of input and may
make a | mistake in interpretation.
48
chronic pain
Pathologic Pain; occurs beyond the usual course of an acute | disease or after a reasonable time for healing to occur
49
3 types of chronic pain
nociceptive neuropathic mixed pain
50
Nociceptive:
Due to activation of nociceptors
51
Neuropathic:
Due to neuronal injury • Pain is paroxysmal, sharp and stabbing • Pain is associated with Hyperalgesia (increased sensitivity 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.”
52
Mixed Pain
combo of nociceptive and neuropathic
53
autonomic responses are only a part of --- pain
acute
54
Moderate to severe pain can affect function of every organ AND adversely influence postoperative (2)
morbidity & mortality. Poor pain control will worsen patient outcomes!
55
Nociceptors are usually found on free nerve endings and | are sensitive to: (3)
1. Mechanical Stimuli 2. Thermal Stimuli 3. Chemical Stimuli
56
Chemicals known to excite nociceptors: (9)
``` Substance P, ATP, calcitonin gene related peptide (CGRP), glutamate, aspartate, Bradykinin, potassium, Histamine, serotonin ```
57
Chemicals known to sensitize nociceptors: (4)
Substance P, Prostaglandins, Histamine, Bradykinin
58
Chemicals known to inhibit nociceptors: (3)
Enkephalins, β Endorphin, Cannabinoids
59
Summation of | nociception is ---
spatial (based on # of receptors activated).
60
``` Minimal adaptation and a nociceptors activity actually --- if the painful stimuli continues (hyperalgesia) due to nociceptor sensitization ```
INCREASES
61
Allodyina
painful sensation to a innocuous stimulus can occur too
62
``` “Stimulation of nociceptors also leads to antidromal (reverse) activation of nociceptive nerve terminals and release of (2). Release of these peptides causes (5) ```
substance P and calcitonin gene related peptide ``` mast cell degranulation, vasodilation and edema, and further sensitization and activation of nociceptors (neurogenic inflammation).” ```
63
Triple Response (3)
``` 1. Red flush around site of injury (flare) 2. Local tissue edema 3. Sensitization to noxious stimuli ```
64
Tissue injury leads to local release of --- that excite or sensitize nociceptors causing ---
endogenous inflammatory mediators (ex. Histamine, Prostaglandins, Bradykinin, etc.) Hyperalgesia
65
Aδ Fibers:
Small, Myelinated, 12-30 m/sec (fast) – Neurotransmitter includes Glutamate – Sharp, localized pain (FAST PAIN) – Thermal and Mechanical Stimuli
66
C Fibers:
``` Unmyelinated, 0.5-2 m/sec (slow) – Neurotransmitter includes Substance P – Dull, diffuse pain (SLOW PAIN) – Thermal, Mechanical and Chemical Stimuli ```
67
The second order neuron crosses over in the --- --- to the opposite side of the spinal cord to ascend contralaterally.
anterior commissure
68
divisions of the Spinothalamic Tract (2)
Neospinothalmic | Paleospinothalamic
69
Neospinothalmic:
Mostly A delta fibers. Provides location, intensity, & duration information.
70
Paleospinothalamic:
Mostly C fibers. Some of these 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.
71
There are multiple alternate pathways: (3) i. Spinoreticular pathway. Mediates ii. Spinomesencephalic pathway. Activates iii. Spinohypothalamic pathway. Activates
arousal & autonomic responses anti-nociceptive, descending pathways the hypothalamus
72
The Spinothalamic Pathway includes the
Neospinothalamic and Paleospinothalamic | Tracts
73
Spinothalamic Pathway | First Order Neuron:
cell body in dorsal root ganglion (or somatic afferent ganglion of cranial nerves).
74
Spinothalamic Pathway | 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.
75
Spinothalamic Pathway | Third Order Neuron:
cell body in thalamus, axons project to the sensory cortex. Sensory Homunculus
76
First- and Second-Order Neurons | Synapse in the
Dorsal Horn of the Spinal | Cord
77
Spinal cord gray matter was divided by Bror Rexed in the 1950s into ten ---. I-VI are in the dorsal horn.
laminae
78
Second-order neurons in the | dorsal horn are either:
1. Nociceptive-specific Neurons 2. Wide Dynamic Range (WDR) Neurons
79
Nociceptive-specific neurons | receive
only noxious stimuli
80
WDR neurons also receive
non- noxious afferent input from Aβ, Aδ, and C fibers
81
``` --- neurons are the most prevalent cell type in the dorsal horn (most abundant in Lamina V). ```
WDR
82
Wide Dynamic Range Neuron
``` During repeated stimulation, WDR neurons characteristically increase their firing rate exponentially (wind-up), even with the same stimulus intensity. They have larger receptive fields than nociceptive-specific neurons. ```
83
Nociceptive Specific Neuron
``` Found in lamina I and have discrete, somatic receptive fields; they are normally silent and respond only to high- threshold noxious stimulation, poorly encoding stimulus intensity. ```
84
Mechanisms for CENTRAL Modulation of Pain (3)
Facilitation of Pain 1. Wide-Dynamic Range (WDR) Neurons found in the dorsal horn of the spinal cord. They respond to all somatosensory modalities. Normally only sensitive to non-noxious stimuli UNLESS the stimulus is highly noxious. Allodynia = Perception of non-noxious stimuli as pain 2. Receptor Field Expansion of dorsal horn neurons so adjacent neurons become responsive to stimuli (whether noxious or not) 3. Some second order neurons increase their frequency of activation following prolonged discharge—”wind-up.” May continue, even after the nociceptive stimulus is removed.
85
Mechanisms for CENTRAL Modulation of Pain | Inhibition of Pain (2)
gate control theory of pain | pain inhibits pain
86
Gate Control Theory of Pain:
Activation of Ab fibers from the same region inhibits the Spinothalamic pathway and reduces pain perception The A-β fibers activate an inhibitory interneuron that causes post-synaptic inhibition of the Second-order neuron for the Pain Pathway. This inhibition leads to a weaker pain signal being sent to the thalamus and somatosensory cortex. This is the basis for how massage therapy and TENS units work as a treatment for chronic pain conditions and is why rubbing a painful region makes it feel better.
87
Pain Inhibits Pain
``` Stimulate pain in other regions of the body to inhibit pain (via GABA) at second order, WDR, neurons in spinal cord (Diffuse Noxious Inhibitory Control (DNIC) or Conditioned Pain Modulation (CPM)) ```
88
Conditioned Pain Modulation | CPM
a second noxious stimulus leads to the activation of PAG, NRM and RVM in the brainstem, which results in diffuse analgesic effect over the rest of the body. “Pain Inhibits Pain” Interneurons in the dorsal horn of the spinal cord are activated by 5-HT/NE and release endogenous opiates (Enkephalin). Enkephalin in the dorsal horn inhibits the first-order and second-order neurons (nociceptive specific and/or WDR neurons).
89
In ---, there is evidence of low concentrations of serotonin and NE in the CSF, which suggests this pathway might have reduced activity.
Fibromyalgia
90
Analgesia is the
selective suppression of pain without | effects on consciousness or other sensations.
91
We use many mechanisms to achieve pain relief: (5)
1. Pharmacological agents: COX Inhibitors (aspirin, ibuprofen), Opioids, Antidepressants (TCAs), Anticonvulsants (GABApentin), Topical Lidocaine & Capsaicin 2. Massage (Gate Control Theory of Pain) 3. Acupuncture (seems to be linked to activation of the endogenous opioid pathways) 4. Transcutaneous Electrical Stimulation (TENS) 5. Nerve Blocks
92
Pain information from the orofacial region is | conveyed into the CNS via the (2)
Trigeminospinothalamic Tract and the | Trigeminoreticular Tract
93
Pain can be referred to the orofacial region | particularly teeth) in response to: (5
* Maxillary Sinusitis * Angina * Migraine * Nasal Mucosa * Ear Pain
94
It is often difficult to -- tooth pain.
localize
95
Dentin and enamel has limited space to swell in the --- state, so results in
inflammatory | exaggerated pain even with mild inflammation
96
Painfully noxious hot/cold stimuli do not cause pain in an uninflamed healthy tooth due to thermal insulating of the enamel. But, with missing enamel and exposed dentin, a slight thermal stimuli will cause
sudden and stinging pain. – It is difficult to distinguish between between noxious hot or cold stimuli.
97
Weak air puffs to exposed dentin result in
intense pain | while in skin this would result in the sensation of light touch.
98
Stimulation of tooth pulp by any kind of stimulus results in a
painful sensation
99
While afferent fibers innervating teeth comprise only 0.1% of trigeminal neurons, each of these fibers has extensive branching, such that each afferent nerve innervates
multiple teeth.
100
Large receptive fields =
Poor Localization
101
The pulp is highly innervated with sensory afferents, mostly for pain, but the dentin has limited innervation but is sensitive due to
dentinal tubules. | Nerve fibers penetrate the dentinal tubules, but only for a short distance into the inner dentin.
102
Odontoblasts have long processes that are located in the --- --- and their cell body is on the surface of the --- ---
dentinal tubule | dental pulp
103
``` Studies have shown that sensitive teeth have many more (8X) and wider (2X) --- --- compared to non- sensitive teeth. --- --- thought to be more important than number since flow is proportional to the fourth power of the radius. ```
dentinal tubules Tubule radius
104
Tissue is highly vascular, contains many neurons, but is a | --- tissue because it is surrounded by
low-compliance | hard tissue
105
Any change in volume within the tooth pulp translates to large changes in pressure (3)
a. Inflammation due to mechanical or bacterial trauma b. Increases in pulpal temperature secondary to laser radiation c. Can lead to hypoxia and eventually tissue necrosis
106
Dentin is a mineralized, avascular tissue (3)
a. Suprasensitive to extreme temperatures, particularly at the neck of the tooth (gingival recession, wear of cementum and enamel) b. Sensitive to hyperosmotic solutions c. NOT sensitive to KCl, bradykinin, and histamine
107
Dentinal tubules contain odontoblasts and perhaps they also | contain
nerve terminals
108
The mechanism of --- --- in dentin is not currently | understood.
pain transduction
109
``` Dentinal and pulp nociceptor information travels via Aδ and C fibers along with Aβ. The nerve fibers in tooth pulp are ~90% ```
C-fibers
110
Dentinal Pain:
sharp pain
111
Pulp Pain:
dull pain
112
Dentin and Pulp are separated | by
tight junctions between epithelial cells—selectively permeable barrier
113
Neural Theory
``` Free nerve endings in dentinal tubules are activated ```
114
Hydrodynamic Theory
``` Stimulus displaces fluid in dentinal tubules which activates mechanoreceptors in nerve endings of dentin or pulp. ```
115
Odontoblast | Transducer Theory
``` Odontoblasts are excited and transduce the signal to nearby nerve cells ```
116
TRPV1
``` Polymodal receptor activated by painful chemicals (Capsaicin) and noxious temperatures (above 42°C) ```
117
TRPM8
Low Temperature (threshold 25°C)
118
TRPA1
``` Low Temperature (threshold 17°C) Mechanosensation? ```
119
The periodontal ligament has (2)
``` nociceptors AND Ruffini Endings (a mechanoreceptor/proprioceptor). ```
120
Periodontal nociceptive information from free | nerve endings travels via
Aδ/C fibers
121
``` The --- --- regulate the forces applied by the teeth in occlusion, mastication and biting. These receptors are slowly adapting, show directional sensitivity and their response varies with the force applied to the tooth. ```
``` periodontal mechanoreceptors (Ruffini endings) ```
122
Subjects with dentures (who lack corresponding PDL receptors), show impaired -- ---- perception in tasks as biting force discrimination
intraoral sensory
123
the apical portion of the periodontal ligament is the most heavily ---
innervated