Medial Pain Flashcards
Nociception vs. Pain
-Pain is emotion, nociception is sensation
Five main functions of the medial pain system
- Limbic and autonomic activation
- Learning and anticipation
- Nocifensive behavior
- Empathy
- Inhibition
Three main ascending spinal pain systems
- Anterolateral system (direct): includes neospinothalamic tract (axons primarity in lamina 4 of dorsal hort, travel in lateral funiculus to VPL and then somatosensory cortex)
- Anterior lateral pathways (indirect): controls limbic, autonomic, endocrine and motor components of pain, and the activation of pain-inhibiting circuits. Bilateral ascention, multiple synapses
- Posterior medial pathways: visceral nociceptive information in gut. Lamina X neurons synapse in gracile nucleus and then project of VPL and CL of thalamus, then to insula and anterior cingulate cortex
3 indirect anterior lateral ascending pathways
- Paleospinothalamic: ascend bilaterally, synapse in RF and MITN, project to limbic cortical and subcortical areas (ACC and insula)
- Spinoreticular: ascend bilaterally, terminate at two different levels of RF (caudal sends back to IML cell column, rostral RF and LC innervate PVN and MITN)
- Spinomesencephalic: Parabrachial nucleus and PAG, visceral info, PAG regulates ANS and alters signals to amygdala, inhibit pain sensation
Referred pain
-Some visceral nociceptive info synapses in neurons in the dorsal horn which can be perceived as cutaneous pain from segmentally related dermatomes.
Myelotomy/Cordotomy
- For intractable visceral pain
- Deafferent the source of the pain signal-posterior midline myelotomy
Reticular formation subdivisions important for pain
-LC, parabrachial area, nucleus gigantocellularis, raphe nucleus
Key projections of RF, LC, MITN, and PAG
- Innervate key upper and lower limbic/autonomic/motor structures
- Nucleus ambiguus
- Gigantocellular RF that projects to the sympathetic IML
- Parabrachial nucleus
- Paraventricular nucleus of hypothalamus
- Amygdala
- ACC
- Support limbic/autonomic activation!!!!!
Cingulate activation in the medial pain system
- Motor and limbic areas strongly activated
- Noxious visceral stimuli more rostral than cutaneous stimulations
- Activation also includes supplementary motor area and cingulate motor area–motor planning
Medial pain system interaction with limbic system
-Allows limbic system to assign emotional weights to stimuli (rating unpleasantness activates ACC, attending to location activates MCC)
Anticipation/learning and Nocifensive Behavior
- Contingent negative variations appear in EEG recordings several seconds after a fear inducing stimulus
- ACC activity co-varies with amplitude of this potential
- Anticipation of pain is a learning event in the medial pain system
Central sensitization
- Maladaptive learning
- Noxious stimulus leads to greater intracellular Ca2+
- Sensitized nociceptors have greater amounts of Ca2+ which causes long periods of abnormal depolarization in spinal cord neurons and their targets
- Unchecked central sensitization processes can lead to a state of near constant nociceptor firing and thus chronic pain
Pain empathy
- Seeing pain inflicted on others activates lateral nociceptive and medial pain systems
- Can evoke equivalent emotions and sympathy pain
Anterior cingulotomy
- Treatment of debilitating chronic pain
- Abolishes nocifensive and many limbic/autonomic responses
- Patients can still localize noxious stimuli
- Can feel the stimulus but don’t care
Pain inhibition
- Magnetic cortical stimulation gives significant pain relief
- Increased ACC activation and consequent PAG activation
- MCS activates descending pain signaling pathways from ACC
