BIO448-Pain

neurociception

perception of the sensation of pain

thermoreceptors

receptors involved in relaying information about the temperature BELOW the pain threshold

They still fore at higher temperatures, but the maximum response is already reached so they plateau. This implies that pain involved specialized neurons.

increasing activity as temperature increases

nociceptors

pain receptors

only activated starting at hot temperature, aka has an activation threshold

A-delta fibers

fibers responsible for short term/sharp pain

myelinated fibers

C fibers

unmyelinated fibers responsible for duller, long-lasting pain

polymodal fibers (respond to all painful stimuli like heat, mechanical, chemical) but have preferences for a specific one

A-delta Type I

low threshold for dangerous mechanical and chemical stimulation

high threshold for heat

A-delta Type II

low threshold for heat

high threshold for dangerous mechanical and chemical stimulation

VR-1

capsaicin binds to vanilloid receptor 1 aka ___.

• as a nonpolar molecule, it goes straight through membrane and binds to ___ intracellularly causing the pore to open and let Na+ and Ca2+ through. This depolarizes the receptor and creates action potential.

• this receptor also responds to heat and protons, but they bind extracellularly

found on both A-delta and C-fibers

transient receptor potential

TRP

a family of ion channels which respond to different environmental stimuli

ionotropic receptors made of multiple different proteins

capsaicin

TRVP-1 channel responds to ___

menthol

TRPM8 responds to ___

mustard

TRPA1 responds to ___

ligand

Each TRP channel typically responds to both a chemical ___and cold/heat

anterolateral

Pain information travels to the cortex in the ___system

pain neurons come in through the dorsal horn of the spinal cord, synapse on motor neuron in spinal cord

the motor 2nd order neuron immediately decussates before going to brain along anterolateral tract

different

A-delta and C-fibers pain neurons synapses on ___ things in dorsal horn

pain pathway

• 1st order neuron enters spinal cord and synapses in dorsal horn

• 2nd order neurons have cell bodies in dorsal horn, CROSS-OVER w/in same level of spinal cord, travel up anterolateral tract system, synapses in thalamus VPL.

  • same as normal sensory info from lower body

• 3rd order neurons have somas in VPL of thalamus and synapse in primary somatosensory cortex

same, opposite

touch fibers come from the ___ side, while pain fibers come from the ___ side.

discriminative pathway

pain pathway giving info about the location, intensity, and quality of painful stimuli

synapse in ventral posterior nucleus of thalamus

Affective-motivational pathway

pain pathway transmitting info about unpleasant feeling, fear, anxiety, fight-flight reaction

synapses in regions of brainstem and diencephalon (amygdala, hypothalamus, etc) but ALSO in midline thalamic nuclei to go to anterior cingulate cortex

somatosensory cortex

changes in pain intensity are integrated in ___

cingulate cortex

changes in unpleasantness are integrated in ___

cingulate cortex

1st gyrus at the bottom of cortex in frontal lobe

how touch modulate pain

there are interneurons sitting in dorsal horn of spinal cord that are connected to both pain and touch sensory neurons

• touch neurons release glutamate which activates the interneurons that then inhibits the activity of the pain fibers by releasing GABA

• interneurons also directly connected to pain 2nd order neurons and inhibit them using GABA

central

perception of pain is subject to ___ modulation, aka descending neurons have an effect on the perception of pain

• including placebo effects: the body’s own opioid receptors which are influenced by Raphe nuclei

endogenous opioids

• enkephalins

• endorphins

• dynorphins

act on metabotropic receptors in interneurons