Physio-Pain and Temperature (Brownell) Flashcards
What is nociception?
sensing pain (and also temperature).
What is the mechanism of nociception?
- C type nocioceptors release Substance P and CGRP as neurotransmitters
- Release from local peripheral nerve ending stimulate histamine release from mast cells and vasodilation (inflammatory response)
- Macrophages and damaged epithelial cells secrete growth hormones, cytokines (IL-1b), Bradykinin, ATP, H+, all of which hypersensitize pain response.
What are the characteristics of nociception?
- Sensitivity to tissue damaging stimuli and high/low temperature.
- Associated with ‘free nerve endings’:
- Aδ (partially myelinated, 5-30 m/sec) or ‘fast’ pain and ‘C’ (unmyelinated, ~1m/sec) ‘slow’ pain fibers
What are the two experiential components of pain?
- Discriminative: fast, tingly/itchy /sharp ‘first’ pain)
2. Affective/motivational: slow, dull, persistent ‘second’ pain. (eg. recall the hammer hitting your finger).
What does it mean when we say that Aδ and ‘C’ fiber subclasses are ‘polymodal’?
In addition to mechanical stimuli, they respond to heat, cold, acid, noxious chemical, growth factors, neurotransmitters, and hormones
What are thermoreceptors? What is the Capsaicin receptor?
• Cold and warm receptors that increase activity during those times.
• Capsaicin receptor is a member of the Transient Receptor Potential (TRP) superfamily w/ several other herbal stimulants.
-It is a heat receptor on the tongue that is the same as the receptor for body temperature. (same thing w/ menthol)
What is the distribution of thermoreceptors?
- Head: 21%
* Trunk: 38%
Describe the TRP family. What is a polymodal response?
- TRP family is diverse, everywhere, and is the source of transduction for thermal, cold, and mechanoreceptors.
- Polymodal response: Many “adequate” stimuli associated with tissue injury or damage
- Mechanical, chemical, thermal, and noxious irritants
Describe the transducer mechanism.
- Transducer mechanism commonly involves TRP superfamily of genes/proteins acting as gates for cationic (Ca or Na) ion channels in all animals (highly conserved: affinities to other 6 transmembrane ion channels). Ca acts as second messenger)
- Subfamilies of TRP genes are very common (also associated with non-nocioceptive functions in other cells and tissues).
Describe cancer pain.
o Nocioceptors are polymodal and responsive to noxious, thermal, mechanical and chemical side effects associated with growth factors secreted by tumors.
What pain transmission pathway to the CNS is described as: Aδ myelinated fiber projecting to DH layer 5, to contralateral Anterolateral (Spinothalamic) tract to VPN, and Somatosensory Cortex (S1)?
Fast or Discriminitive Pain
What pain transmission pathway to the CNS is described as: ‘C’ type noxious pain/temperature unmyelinated fiber terminating in DH 1&2 (substantia gelatinosa); enters contralateral Anterolateral Tract, branches to midbrain reticular formation, thalamic VPN and anterior cingulate & cuniform cortex.
Slow or Affective-motivational Pain
What are the spinal cord connections?
1.Pain pathway (“C” fibers) enter Lissaurer’s tract for 1-2 spinal segments (anterior/posterior), terminate in lamina 1&2 (substantia gelatinosa), synapse on 2nd order afferents, cross cord, ascend Anterolateral tract
2. Aδ fibers terminate in lamina 1&5, 2nd order fiber crosses cord and ascends Anterolateral tract.
Some lamina 5 cells receive visceral sensory input, the basis of “Referred Pain” (see next).
Non-nocioceptive pathway ascends dorsal column/lemnical tracts
What is referred pain?
Convergence of visceral and somatic afferents w/n the DCML projection to thalamus and Insular cortex.
What is the Descending analgesic pathway? Where does it originate? What is the path? Give an example.
-Modulate the transmission of ascending pain signals.
-Comes from the cortex.
-Midbrain periaqueductal gray nucleus → dorsal raphe nuclei → blocks pain stimulus in the dorsal horn of the spinal cord.
-Example: acupuncture and placebo effect.
• Tricks the brain into turning off the original pain pathway.
