Somatostatin 2 Flashcards
What major pathway of the somatosensory system is responsible for pain?
Spinothalamic tract (anterolateral system)
What are Nociceptors and thermoreceptors?
Nociceptors are neurons specialized for the detection of painful stimuli
Thermoreceptors detect non-painful levels of heat
How do A fibres and C fibres contribute to different aspects of pain?
On image
What does The TRPV1 receptor do?
What is the agonist for it?
The TRPV1 receptor is involved in transduction of noxious heat
How do we maintain nociceptive activity after injury?
‘Inflammatory soup’ of cytokines, prostaglandins and small signalling molecules maintains depolarisation and sensitivity of C-fibre terminals after original stimulus
• Hyperalgaesia -increase sensitivity to pain
• Allodynia – painful response to a repose that would normally not hurt after injury
Describe the pathway of the anterolateral system
Dorsal horn interneurons
Located in superficial and deep layers of dorsal horn
Synaptic input from C- and A-δ fibres
Axons cross and ascend in anterolateral white matter
Some are multi-modal (receive convergent nociceptive and non-nociceptive inputs)
Some receive convergent input from visceral afferents
What is referred pain
pain is felt somewhere else caused by convergence of visceral afferents onto the second-order interneurons receiving there c fibres and a delta fibres from a particular region of the body
Describe the STT pathway
- STT projects to S1 via VP nuclei of thalamus (like DCML system)
- however, STT and DCML axons do not converge on same thalamic neurons – pathways are parallel
- S1 is necessary for the localization of pain, but stimulation of S1 gives rise to referred tactile, not painful, sensations
- Additional areas are involved in pain sensations
What are the 2 systems in central pain processing?
• Diverge at level of thalamus
• Lateral system (do not confuse with anterolateral system)
o VP nuclei of thalamus, in parallel with DCML system
o Primary and secondary somatosensory cortex (SI and SII)
• Medial system
o Midline nuclei of thalamus (intralaminar)
o Anterior cingulate and insular cortex
Describe the lateral and medial pain systems
Lateral
• Sensory-discriminative
• Project via specific somatosensory thalamic nuclei
Medial
• Affective-motivational
• Project to different cortical areas via (non-specific) midline thalamic nuclei
How can pain be treated?
Successful at treating pain as neurophysiological response to tissue damage
• NSAID
• Opiate drugs
Chronic pain
• antidepressants (e.g., amitriptyline, duloxetine)
• At lower dosage and in absence of diagnosis of clinical depression
What is chronic pain?
3 months
• Alarmingly high prevalence
• May be due to nerve damage from prior injury: neuropathic pain
• However, increasingly accepted that pain can be dissociated from tissue damage
• What could that mental image be? Well we have substrates for the location and identification of pain and also for the affective aspects of pain, if even if they’re not proven. But the principle that pain could be a sort of hallucination (real pain for all that) follows from any representational view of the mind.
• If wind-up can be considered an explanation for neuropathic pain, then the same principles apply to higher circuits, whatever they may be, but plausibly involving activity in medial pain pathway. We can try to test this. What about neuroimaging? Maybe differences when averaged across groups, but not enough to look at any one image and classify as experiencing chronic pain or not.
How can pain be dissociated from tissue damage?
The tissue damage model of pain. Doctors are trained in this and they will look for tissue damage, and quite plausibly, find it. The problem is that the tissue damage is not correlated with the level of pain, when you compare across individuals. If you have a pain in a tissue that hasn’t existed for years this alone suggests that pain is in the mental image of the body rather than the body itself.
• Phantom limb pain
• Central pain
