Pain and Temperature Sensations Flashcards
Core Body Temperature
37⁰ C
Body temperature has a
circadian fluctuation of
- 5-
0. 7°C (1-1.5° F)
Temperature is lowest at
—, highest in the —
6:00am
evening
Temperature regulation is less
precise in
young children;
normally have a temperature
that is 0.5°C or so above adults.
Thermal Receptors (thermoreceptors) are on
free nerve endings
& commonly found in the skin. Also in hypothalamus, spinal cord,
& deep tissues.
Categorized by their different sensitivities: (2)
cool
warm
Cool and warm receptors innervate
discrete regions of skin
There are – times as many cool receptors at any skin surface
3-10
— are activated by extreme cold or heat
Nociceptors
Which do you perceive first- a thermal or mechanical sensation?
mechanical
After thermoreceptors are activated,
Warm signals are transmitted by:
Cool signals are transmitted by:
C and Aδ fibers
Aδ and C fibers
The mechanism of thermal sensation is most likely achieved by
sensing a change in
metabolic rate
— increases the rate of intracellular chemical
reactions
Temperature
Several Transient Receptor Potential (TRP) channels
have been identified, each sensitive to a different
temperature range. Some chemicals (Capsaicin, Menthol)
elicit thermal sensations, too.
Temperature Perception
Based on the Activation of a
Combination of the Receptors
COLD PAIN: (5)
Tickling, Pricking, Aching, Burning, Numbing
HOT PAIN: (5)
Sharp, Pricking, Stinging, Burning, Throbbing
If skin reaches —, cold/pain fibers are no longer stimulated.
freezing
At ~ –°C, heat/pain fibers are activated.
Sometimes cold fibers are activated, too—
45
paradoxical cold
Average skin
temperature =
34-35ºC;
equal activation of cool
and warm receptors.
Adaptation of Thermoreceptors • They mostly (but never completely) adapt to --- ---; BUT they quickly change their activity in response to ---
constant temperature
changes in temperature.
They are very sensitive to changes
in temperature.
Adaptation of Thermoreceptors
• If the temperature reaches one of the
pain thresholds, the sensation
becomes
more persistent throughout
the stimulus
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)
mid-range
Sensitivity of Thermoreceptors
• If nociceptors are simultaneously activated, the system is even
better able to
discern small changes in temperature
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.
There is also an increase in the rate that — receptors fire (but not nociceptors)
thermal
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.
There is a much greater ability for detection of a — stimulus if a large region is activated.
temperature
Receptors are primarily sensitive to —, but certain
receptors are also sensitive to —
temperature
chemicals
Vanilloid Receptor Subtype (3)
- TRPV1 Receptor
- Activated by capsaicin, temperature >43°C, and protons
- Decreases the threshold of channel activation so that
heat is perceived at 33°C.
Cold-Menthol Receptor Type I (CMR1/TRPM8) (2)
- Menthol and related compounds
- Decreases the threshold of the channels so that warmer
compounds are perceived as cold.
Characteristics of Thermoreceptors in Orofacial Region
receptive field size:
Small receptive fields (nociceptive thermal receptors
have large receptive fields)
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
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
Characteristics of Thermoreceptors in Orofacial Region
Thermoreceptors in — are the most sensitive to
changes in temperature.
tongue
Due to activation of nociceptors. This usually results in the
perception of
PAIN, an unpleasant & emotional experience
associated with actual or potential tissue damage.
nociception and pain relationship
All nociception produces pain, though not all pain
results from nociception.
Unlike most sensory modalities, pain can be evoked
by
any stimuli (mechanical, thermal or chemical) if it is strong enough.
We sense pain so that the body can (3)
detect, localize, and limit tissue damage.
PAIN, whatever its cause, is never —. Pain is the
most common reason patients (2)
benign
seek healthcare AND the most common symptom of disease.
types of acute pain (2)
somatic
visceral
acute pain
Physiologic Pain; <6 months duration
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
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.
Both types of visceral pain can be –
referred
Referred pain most frequently occurs with pain of
— Origin
visceral (& sometimes parietal)
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.
chronic pain
Pathologic Pain; occurs beyond the usual course of an acute
disease or after a reasonable time for healing to occur
3 types of chronic pain
nociceptive
neuropathic
mixed pain
