Nociception-Pain-Temperature Flashcards
Spinothalamic Tract path
C and Ad (cell body in DRG) Ipsilateral Spinal Gray Matter Decussates in Anterior white commissure (spine) Ascends contralateral VPL- thalamus sensory cortex
Spinothalamic Tract carries?
pain and temp
Warm fiber?
C
Cool Fiber?
Ad
Touch/ proprioception fiber?
AB
Extreme cold fiber?
C
Extreme Hot fiber?
Ad
First a tolerable, localized, “pricking” pain is detected (___ fiber first pain).
Aδ
Then, a burning,
intolerable, diffusely localized, “burning” pain is experienced (____ fiber second pain).
C
Aδ and C fibers differ. The receptive fields associated with Aδ fibers are _____ than those associated with C fibers.
smaller
Thus, information carried by Aδ fibers will be better localized leading to better
spatial discrimination
Pressure Block of pain
AB (first pain) –> Ad –> finally C (in order)
Local Anesthetics block of pain
C (second pain) –> Ad –> AB
Polymodal nociceptors have C fibers as their
afferents
______ is expressed on polymodal
nociceptors.
VR-1
A __________ is a sensory neuron that responds to potentially damaging stimuli by sending signals to the spinal cord and brain. This process, called nociception, usually causes the perception of pain.
nociceptor
Polymodal nociceptors can be activated by ________________
C fibers as their afferents.
high-intensity mechanical,
chemical or thermal stimuli
Polymodal activation
↑ E-stim: AB stim–> Ad–> finally C (repetitive stim needed)
chemicals that act as pain activators
Bradykinin, acid, K+, serotonin. Depolarize to threshold creating AP
Activators
direct activation of nociceptors
Bradykinin produced by cleavage of an inactive precursor, ___________ (a serum protein).
kininogen
Upon ___________, cytoplasmic proteases are released –> degrade serum proteins–> bradykinin.
tissue damage
Bradykinin directly activates pain receptors of :
Aδ and C fibers.
vanilloid receptor (VR)
The receptor is part of an ion channel complex. When the receptor is activated,
the associated non-selective cation channel opens, thereby leading to a depolarization.
VR-1, is known as the capsaicin receptor. VR-1 is strongly activated by capsaicin and weakly activated by ______
acids and extreme heat
nociceptors that signal extremely cold temperatures (
C fibers.
warm receptors tend to be on
C fibers
C fibers are coated w/
nothing, unmyelinated
information carried by __________ ( lightly myelinated) will reach the CNS before that carried by C fibers.
Aδ fibers
projects to the midbrain periaqueductal gray region (PAG) and is important for descending control of pain.
spinomesencephalic tract
pathway conveys pain inputs that lead to forebrain arousal and elicits emotional/behavioral responses via connections to the emotional circuits of the brain
spinoreticular tract p
a principal pathway and conveys pain information to the thalamus. This tract projects to the nuclei of the ventral posterior thalamus, which includes VPL. Neurons in these nuclei process information related to localization of pain and project to
somatosensory cortex.
spinothalamic tract
Release of Substance P at the dorsal horn synapse produces central sensitization:
(hyperalgesia)
Activation of non-nociceptive fibers leads to activation of dorsal horn interneurons that in turn inhibit synapses activated by:
nociceptive fibers
non-nociceptive afferent pathways (e.g., touch receptors and Aβ fibers).
Rubbing a wound helps
The synthetic drug, __________, blocks the action of opiates.
naloxone
A brain region that is particularly sensitive to opiate actions is the
PAG.
Opiates also inhibit transmission in the _________ of the spinal cord
dorsal horn
brains own opiate-like compounds.
enkephalins, β-endorphin and dynorphins and are collectively known as endorphins
Stress Activates PAG –> inhibition of
2o neurons of the dorsal horn.
_______ blocks some but not all
of the analgesia produced by stressful situations
Naloxone
In the dorsal horn of the spinal cord, _______ is the major inhibitory transmitter.
GABA
Following injury of C fibers, Aβ afferents sprout and invade the normally forbidden territory of the:
substantia gelatinosa
second-order neurons in the substantia gelatinosa that are normally activated only by pain input are now also activated by non-noxious stimuli.
Nervous systems of patients experiencing
chronic pain are__________ from those who have not had the same experience.
functionally and structurally different
changes are diverse and range from changes in excitability, neurotransmitter
content, synaptic efficacy, to circuitry.
A very telling observation is that administration of naloxone blocks the
placebo effect.
Stress can activate:
PAG
DOes Nalaxone block stress analgesia?
Only partially.
THC does the other bit
Thus, stress–induced analgesia involves both ____________________ mechanisms
opioid and nonopioid mediated
spinomesencephalic tract projects to the midbrain ___________ and is important for descending control of pain
periaqueductal gray region (PAG)
Stimulation of the periaqueductal gray region (PAG) in the midbrain produces a powerful:
analgesia
Touch, pressure and temperature sensations persist and only pain
sensation is attenuated.
PAG neurons project to the __________ in the medula
nucleus raphe magnus
nucleus raphe magnus neurons in this medullar region are:
serotonergic (i.e., use serotonin as their neurotransmitter)
In the spinal cord, serotonin will lead to inhibition of second-order neurons of the dorsal horn by exciting an inhibitory interneuron.
This interneuron uses enkaphalin
enkephalin mechanism
presynaptically (block of voltage-gated calcium current)
postsynaptically (opening of potassium channels).
