2.2 - pain + temperature

glossary

agonist

chemical compound that can mimic the function of a receptor’s physiological ligand

antagonist

chemical compound that inhibits the function of a receptor

chemoreceptor

sensory receptor that can be activated by chemical ligands

polymodal receptor

sensory receptor that can detect multipel types of stimuli

generator potential (receptor potential)

graded porential generated due to the opening of gated ion channels on a sensory receptor neuron/ cell

superficial pain

pain originating from the surface of the skin or of the mucous membrane

somatic pain

pain originating from deeper tissues, such as the deeper layer of the skin or the muscle/tendon/bone

visceral pain

pain originating from internal organs

whar are the two types of pain signals after a pain stimulus

first and second

first pain signals

processes for sensory discrimination/localization in the somatosensory cortex

second pain signals

processed for affective/emotions in other areas in the pain matrix

parallel pain processing

simultaneous processing of first and second pain signals by 2 anatomically disinct neural circuits

pain matrix

brain areas involved in the processing and integration of pain signals

first pain

sharp, well-localized pain sensation transmitted by the faster Aδ pain fiber neurons to somatosensory cortex

second pain

dull, throbbing and diffuse pain sensations transmitted by the slower non-myelinated C fiber neurons to the pain matrix outside of the somatosensory cortex for emotion and motivation aspects of pain

anterolateral pathway

1) Aδ nociceptor neuron enters into spinal cord at spinal dorsal columns

2) interneuron crosses over spinal cord

3) thalamic neuron synapse w/ somatosensory cortical neurons

*contralateral!!

PAG (periaqueductal grey area)

region in midbrain that has multiple nuclei and is involved in multiple functions, including pain modulation.

what does the PAG secrete to mitigate pain signal transmission to the brain, thus lessening the pain sensation?

endorphins

spinal cord gate theory of pain control

Aβ mechanoreceptor neurons, upon activation by pressure stimuli, can increase spinal interneuron activity— which can then inhibit pain signal transmission by neighboring C fiber neurons

palcebo effect

when a pharmacologically inert drug can elicit beneficial physiological response, such as pain sensation mitigation

what is the potential mechanism underlying the placebo effect?

endophin secretion by the brain to inhibit pain signal transmission to the brain

dissociation of pain and touch sensation

loss of pressure/ tactile and pain/ temperature sensations at opposite sides body, such as in the case of spinal cord hemisection

how are pressure/ tactile signals transmitted

ipstilaterally up the spinal cord until they cross over at the medulla

how are pain/ temp signals transmitted

cross over as soon as they are transmitted contralaterally up the spinal cord

referred pain

when visceral pain is perceived as superficial pain at a different location in the body

what is the possible mechanism underlying referred pain?

could be the convergence of sensory neurons from a skin area and from a visceral organ onto the same spinal interneuron to relay their sensory signals to the brain. the brain thus misinterprets that pain signals from the visceral came from the superficial

phantom pain

perception of pain coming from a missing body part

where does phantom pain possibly originate from?

cortcal mis-organization after body part removal, from aberrant spinal neuron activation after injury or from pain stimuli derived from peripheral neuromas at the site of limb severance

3 types of thermoreceptors

warm, cold and pain

four major types of nociceptors

thermo, mechano, silent and polymodal

• all located in skin, viscera and joints