43 Perception of pain Flashcards
Which of the following is true?
A. Nociception is the reception of noxious signals that indicates potential damage
B. When there is nociception, there will be pain induced
C. Nociception always involves in pain sensation
A only
B: nociception without pain when there is supraspinal antinociception
C: pain without nociception in phantom limb
In acute pain, it is caused by actual noxious stimulation, and typically involves ________________ conducted by ___________ fibers; duller, slower onset pain sensations are conducted by _______________ fibers.
fast, sharp, well localized “first pain”;
alpha-delta;
C
Give examples of chronic pain and briefly describe it.
- Hyperalgesia = increased pain due to mild noxious stimuli
- Allodynia = pain evoked by non-noxious stimuli
- Spontaneous pain spasm = pain in the absence of stimuli
______________________ play critical roles in the transduction of noxious signals in the terminals of pain fibers.
TRPV1 TRPV1 (transient receptor potential vanilloid type 1 channels)
What are nociceptors? Give examples.
High threshold receptors that are free nerve endings.
- Thermo-nociceptors
- Mechano-nociceptors
- Polymodal nociceptors
Describe the flow of events when nociceptors are stimulated.
- Chemical released from damaged tissue like histamine, 5-HT, prostaglandins, bradykinin, K+ excite nociceptors at nerve endings
- Chemical released from free nerve endings include substance P, CGRP (Calcitonin gene-related peptide) to dilate blood vessels and increase mast cell release of histamine
- Chemical like glutamate and substance P released from nociceptive afferents at dorsal horn excite dorsal horn 2nd order neurons
Nociceptors can be sensitized by ______________ upon damage.
prostaglandins
What are the different nociceptive fibers involved in the conduction of noxious signals? Describe according to the speed of conduction, type of pain, the position of synapse within the dorsal horn of spinal cord and distribution.
- Thin myelinated Alpha-delta fibers: fast conduction, fast, first pain, localized;
in laminae 1 and 5; in body surface, muscles, joints
2. Unmyelinated C fibers: slow conduction, slow, delayed and chronic pain; lamina II (SG), present in most tissues
What is the gate control theory?
Some neurons are innervated by A-beta fibers (non-noxious fibers) for gating pain.
When gate opens, C fiber can send signals to projection neurons.
When gate closes, A-beta fibers send signals to inhibitory interneuron to inhibit projection neuron
The nociceptive afferents release____________ and ___________ to excite dorsal horn neurons.
glutamate and substance P
The main pathway of pain sensation projection is? Describe.
Spinothalamic tract.
From spinal cord to the ventral posterolateral nucleus of the thalamus, joint with those from the trigeminal nucleus that terminate at the ventral posteromedial nucleus of thalamus
> primary somatosensory cortex > perceive the location of pain
Other than spinothalamic tract, name and describe the route and functions of the 2 pathways involved in projection of pain.
- Spinoreticular pathway
- relay to reticular formation in the pons and medulla
- convey pain signal to both somatosensory and association cortex (insular cortex, cingulate cortex, prefrontal cortex)
- related to the emotional part of the pain - Spino-mesencephalic pathway
- terminate at the periaqueductal gray in midbrain
- involved in descending control of pain perception
What is projected pain?
Give examples.
Projected pain is pain that is not originated from any nociceptors;
Examples
1. discharge of action potential from the ulnar nerve by direct mechanical stimulation at the elbow is projected into the hand
2. Displaced intervertebral disc compressed spinal nerve and pain stimulation is projected onto the area innervated by the spinal nerve
What is referred pain?
Pain that is not originated from the nociceptors where the pain is felt.
Nociceptive stimulation of the viscera produces a sensation of pain not in the affected organ but rather at superficial part of body.
What are the possible explanations to referred pain? (考過！！！！)
- Nerves supplying the referred somatic region and the affected visceral tissue converge onto the same spinal neuron
- The brain learns from experience that the signal more likely comes from the somatic afferents and hence produce wrong perception.
