Pain Flashcards
Can you have nociception without the perception of pain?
Yes. Nociception is the sensory information
What are the three definitions of nociception?
- Perception of injurious stimuli
- Measurable physiological event (AP) with noxious stimuli
- system that caries info about inflammation or damage in tissue
What is pain?
How is it different from nociception?
Pain is the perception of the noxious stimulus so the unpleasant sensory or emotional experience associated with actual, potential or perceived tissue damage.
Nociception is the sense, pain is the perception of the sense.
What are the two major types of pain?
What cause them?
What descriptions do people usually give for each type of pain?
- Nociceptive pain- due to activation of peripheral nocioceptors (sharp, stabbing, achy)
- Neuropathic pain- perception in the absence of noxious stimuli usually due to peripheral nerve damage or CNS injury that disrupts transmission and processing of the painful stimuli (itchy, burning, freezing, prickly, pins and needles)
For pain, what is the center of a Venn diagram for normal pain (nociception) and pathophysiological pain (neuropathic)?
Inflammation
What is paresthesia?
What is dyesthesia?
Spontaneous sensation that occurs without stimulus
Ex. Pins and needles sensation
When the paresthesia is associated with unpleasant stimuli
What is sensitization to pain?
There is a greater intensity of pain perceived for the same amount of Nociceptive input.
What is hyperalgesia?
When a mild Nociceptive stimuli is perceived as strongly painful
What is neuropathic pain?
The perception of pain in the absence of Nociceptive stimuli (as opposed to hyperalgesia where the perception of a painful stimuli is amplified)
What is allodynia.?
When a non-painful sensation (light touch, vibration, temperature) is perceived as painful
Ex. Bed sheets are painful against that persons legs
What is causalgia?
Neuropathic pain that persists after an injury to a peripheral nerve
What is analgesia?
What is hypesthesia(hypoalgesia)?
- Absence of sensation of pain
2. Diminished sensation of pain
What types of fibers sense pain and temperature?
A-delta and C fibers
Many more C fibers than other afferents
What fiber type is the most common sensory afferent?
What type of receptor is the most common sensory receptor?
- c fibers
2. Nociceptive receptors
What type of pain sensation has the highest spatial resolution and why?
Superficial pain because nocioceptors are more densely packed innervating the skin and have distinct receptive fields
How is spatial resolution of receptors graded or measured?
By number of fibers activated
What are the three main classes of nociceptors in the skin?
- A-delta mechanosensitive
- A-delta mechanothermal
- C fiber polymodal nociceptor
How do A-delta and C fibers differ in terms of threshold for activation and Axonal conduction speeds?
A-delta mediate the sharp first pain (activate sooner and at lower threshold, but short duration)
C fibers mediate the second pain (longer diffuse delayed pain)
The process of nociception requires what type of receptor at the nerve endings?
What signals do these receptors respond to?
TRP- transient receptor potential proteins that depolarize in response to mechanical, chemical or thermal stimuli
What type of TRP family receptors are found in a-delta and c fibers that respond to moderate head and capsaicin ?
Vanilloid receptor VR-1
What do VR-1 receptors respond to?
What type of fiber are they in?
Capsaicin and high temp
A-delta and c fibers
What do VR-2 receptors respond to?
What type of fiber are they found in?
Respond to high heat and are found in A-delta fibers
What is the effect of damaged tissue signals on the response of free nerve ending pain perception?
- Damaged tissue releases bradykinin, histamine, and prostaglandins as chemical signals to sensitize the TRP receptors
- Damaged tissue releases substances to augment inflammation
From the dorsal root ganglion, what is the path of pain and temperature fibers in the spinal cord?
- Nociceptive fibers enter the cord and travel up and down the cord a level or two in Lissaurs tract.
- They synapse with their second order neuron in substantia gelatinosa or nucleus propria (rexed 2,3,4) in the dorsal horn
- These neurons cross the midline and ascend in the Spinothalamic tract (anterolateral pathway)
Why is there such a wide overlap in dermatome sensation?
Because of Lissaurs tract
What are the two types of projection neurons in the dorsal horn for Nociceptive response?
- Nociceptive-specific neurons
2. Wide Dynamic Range neurons
What sensory signals do Wide Dynamic Range neurons integrate?
Nociceptive and non-Nociceptive inputs
What is the effect of C fibers on the inhibitory interneurons that synapse on WDR neurons?
What is the effect of A-beta fibers on the inhibitory interneurons that synapse on WDR neurons?
What is the implication of this?
What is this implication called?
C-fibers inhibit the inhibitory neuron on the WDR so the WDR will transmit the pain signal up the spinal cord.
A-beta fibers excite the inhibitory interneurons on the WDR so they will stop the WDR from transmitting signal.
The implication is that if non-Nociceptive and Nociceptive stimuli fire together, the A-beta fiber can “gate” or block the pain fibers from being transmitted.
This is called “gating theory of pain” and is why you rub a pained area to smooth it (pressure overtakes pain)
What are the three tracts of the anterolateral system?
Where do the second order neurons synapse?
What do they regulate?
- Spinothalamic- VPL, VPM of dorsal thalamus
- Spinomesencephalic - hypothalamus, Amygdala (emotion)
- Spinoreticular - reticular formation of medulla, pons, and dorsal thalamus (medullary RF modulates arousal)
What tract do fibers travel in to reach the reticular formation of the medulla?
What does this signal generate?
The spinoreticular tract.
The fibers regulate arousal in response to pain (“wake up! You are in pain!)
What Nociceptive tract brings pain fibers to the primary somatosensory cortex?
What information does this cortical area tell us?
Spinothalamic to VPL(body) and VPM (face) to the primary somatosensory cortex.
Where the pain is located.
What two anterolateral tracts synapse on the dorsal thalamus?
Where do projections from the dorsal thalamus go?
What information does this provide to us about the pain?
Spinothalamic and spinoreticular.
From the dorsal thalamus it projects to the supplementary motor areas, prefrontal cortex, association cortex, limbic areas to determine what the pain is.
What type of pain does not travel in the anterolateral system?
Where does it travel in the spinal cord?
What does it synapse with in the brainstem?
What part of the thalamus does it go to?
What is the ultimate cortical area?
What does this explain about this particular type of pain?
Visceral pain is carried in the dorsal columns to the nucleus gracilis and then to the ventral thalamus and then to the insular cortex.
This is why visceral pain is often difficult to localize and if referred to another place (left arm pain for a heart attack)
What are the four ways we control pain?
- Gating
- Spinal Interneurons
- Descending CNS
- Central perception
What is the major site of descending pain control in the brainstem?
What does it receive input from?
What does it communicate with?
The periaquaductal gray in the midbrain
It receives input from the cortex, Amygdala, hypothalamus, and brainstem nuclei
It communicates with the dorsal horn neurons in the spinal cord through:
-reticular formation
-parabranchial nucleus
- locus ceruleus (NE)
- raphe nucleus (serotonin)
What is the function of endogenous opioids?
What are examples of three opioids?
How do they perform their function?
Where are they made and how are they released?
To modulate central pain.
Three examples are enkephalins, endorphins, and dynorphins
They are used by interneurons in the dorsal horn to relay descending pain modulation via presynaptic inhibition of c fiber terminals.
They are made in various places in the CNS and are released by various mechanisms ranging from exercise high to acupuncture
How did scientists discover that opioids were a released substance and not an electical signal?
They did acupuncture on a rabbit and that rabbit experienced analgesia.
CSF from that rabbit was transferred to another rabbit experiencing pain and the analgesic effect was present in the second rabbit as well.
With opioids, is nociception still present?
Yes, but the c fibers are being inhibited so there will be no pain perception. The painful stimulus is still present though
