Pain: A neurobiological perspective Flashcards
How does the international association for the study of pain (IASP) describe what pain is?
an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage
What are 2 types of pain? describe.
- nociceptive pain (day to day pain); it is stimulated by a noxious stimuli like heat, cold, mechanical force or chemical irritants; results in adaptive, high-threshold pain and it is protective and early warning
- Pathological pain (non-adaptive pain); stimulated by neuropathic pain like neural lesion or positive and negative symptoms; which is usually a result of some type of damage of neurons in PNS and CNS which leads to maladaptive, low threshold pain
What are the spinal cord levels?
- Cervical C1-C5
- Thorasic T1-T12
- Lumbar L1-L5
- Sacral S1 - S2
each division corresponds to a level in the spinal cord
Where do Primary sensory neurons live? (PSN)
in the dorsal root ganglions
What are the types of primary sensory neurons? and their properties
- large light PSN aka A-alpha and A-beta fibers
which are to discriminate touch and proprioception (not typical pain cells) - Small dark PSN aka A-delta and C fibers which respond to pain and temperature
what are the properties of A-alpha and A-beta fibers?
- they are myelinated and large and they conduct impulses rapidly towards proprioception and light touch
What are the properties of A-delta fibers?
- they are lightly myelinated
- medium diameter
- and involved in nociception of mechanical, thermal and chemical stimuli
What are the properties of c-fibers
unmyelinated
- small diameter
- responds to noxious temp and itch as well as nociception
conducts super slowly and known as “secondary pain” because u feel it after the first pain response
What is the specificity theory of pain?
suggests that we have a system dedicated for transmitting noxious stimuli
- suggested by decartes in 1664 and theres a direct, invariant relationship between a psychological sensory dimension and a physical stimulus
What does the gate theory of pain suggest?
that pain can be modulated
- there is a “gate” within the spinal cord that gets opened or closed
- in reality, gate cells are inhibitory neurons and interneurons that will either allow or close off impulses getting into the spinal cord from the sensory systems and distrupts it getting to the brain to be processed further
- A delta and and c- fibers shut off gate cells and open the gate, the large A-beta fibers activate the gate cell and close it to dampen the pain
What is significant about the pain pathways-sensitization?
pain processing is very dynamic and plastic
What is hyperalegsia?
its when signals of pain are amplified (response is amplified)
what is allodynia?
paradoxial pain, where pain towards something that isnt supposed to be painful (pain towards previously innocuous stimuli)
What function does the dynamic-ness of pain pathways serve?
it can be protective for us
What levels can sensitization (amplification towards pain) occur?
at peripheral level and at central level
How does peripheral sensitization occur?
There are mediators of pain upon first contact in the “inflammatory soup” formation, like 5-HT, bradykinin, histamine..etc..
- these mediators dont directly activate a nocicpetor, they bind to receptors ON nociceptors and trigger a second messenger cascade that sensitizes and changes properties of nerve endings therefore, any stimulus that follows will either be amplified or dampened
What is the step by step process of peripheral sensitization?
a mediator like prostaglandin binds to a receptor on the nociceptor (like a-alpha or b-alpha) and that releases a g-protein to go out and activate an enzyme like PKA. PKA activated by G-protein, then phosphorylates sodium channels and changes its conformations, and therefore changes how much sodium enters and the response to the next stimulus