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74 Cards in this Set

  • Front
  • Back
What are the two ascending sensory pathways?
-Dorsal columns
-Anterolateral system (including the spinothalamic tract)
The dorsal columns carry ____ and _____ to the CNS.
vibration and proprioception
The anterolateral system (including ST tract) carries ____ and ____ to the CNS.
pain and temperature
What is nociception?
the neural response to actual or perceived tissue damage
What are nociceptors?
peripheral free endings of primary sensory neurons origniating from the DRG and trigmenal ganglia neurons
What activates nociceptors?
harmful stimuli (damage releases chemicals that activate free nerve endings)
What are the three classes of nociceptors?
What temperatures activate thermal nociceptors?
above 45 deg C and below 5 deg C
Thermal nociceptors have _____ fibers to sense sharp pain
What are the characteristics of A-delta fibers?
-sharp pain
-least myelinated
-relatively small and slow compared to larger A-alpha and A-beta sensory fibers
What activates mechanical nociceptors? What kind of fibers carry their sensory info?
intense pressure; A-delta fibers (sharp pain)
What activates polymodal nocieceptors?
intense mechanical, chemical, or thermal stimuli
What kind of fibers carry polymodal nociceptor sensory info?
C fibers (dull, prolonged, burining pain) that are unmyelinated
What are the two types of fibers that detect painful stimuli?
C fibers and A-delta fibers
What substances are released following tissue damage?
substance P
What causes hyperalgesia?
Substance P causing the release of histamine from mast cells and histamine acting on the free nerve terminals
Explain the chemical cascade that causes pain.
1. injury damages endothelial cells
2. ATP, Ach, 5-HT releaesd from damaged cells
3. Arachidonic acid is released and converted to PGE2 by cyclooxygenase
4. Bradykinin (potent) is released by damaged cells
5. Activated nociceptive terminals release peptides including substance P and CGRP
6. Substance P & CGRP activate mast cells and cause vasodilation/extravasation
7. Activated and damaged mast cells release histamine
8. Histamine activates polymodal nociceptors (C fiber endings)
At what step in the chemical cascade of pain does aspirin act?
the conversion of arachidonic acid to prostaglandin E2 by cyclooxygenase
How do ATP, Ach, and 5-HT released from damaged endothelial cells work?
they sensitize the endings of nerves (don't necessarily cause a full blown nociceptive response)
Where does Bradykinin act? What does it do?
directly on nociceptive endings of A-delta and C fibers;
it activates other cells to release more prostaglandins and inc. inflamm. response
______ is a transmitter of C fibers
Substance P
T/F: A-alpha and A-beta fibers have outputs in both the dorsal and ventral horn
True (they go all the way down to the ventral horn where they might be involved in sensorimotor reflexes)
T/F: A-delta and C fibers generally terminated in the deeper layers of the dorsal horn.
F (they generally terminate in the more superficial layers)
Which specific lamina do A-delta fibers terminate in?
usually layer I (marginal layer)
but can also synapse on layer V
Which specific lamina do C fibers tend to synapse in?
substantia gelatinosa (layer II) on interneurons (excit and inhib)
What layer of the dorsal horn is most pain information coming from?
superfical layers
What is layer I lamina called? What terminates here?
Marginal layer; nociceptive specific (A-delta) fibers and other somatosensory neurons
What is layer II lamina called? What terminates here?
Substantia gelatinosa; either nociceptive (C fibers) or responsive to non-noxious stimuli
What terminates on level III/IV of lamina?
A-beta fibers-responsive to non-noxious (not nociceptive)
What fibers can synapse in layer V?
A-beta, A-delta, C fibers, and nociceptive input from viscera
What type of fibers can synapse in layer VI?
A-beta fibers (muscle/joint input)
What kind of input is there in layers VII/VIII?
polysynaptic nociceptive inputs bilateral
What is the pathway for pain and temperature sensation?
1. come in Lissauer's tract
2. axons travel up or down a couple of segments before they enter SC
3. come into substantia gelatinosa
4. cross in ventral white commissure
Do all pain/temp fibers cross to contralateral side?
No, some stay ipsilateral but the majority do cross over to the contralateral side
Which fibers conduct the fastest?
A-alpha and A-beta
Describe A-alpha and A-beta fibers.
conduct the fastest
have the largest axons
Describe A-delta fibers.
smaller (than A-alpha & A-beta)
somewhat slower (than alpha and beta) but still pretty fast
Describe C fibers.
conduct orders of magnitude slower (than A fibers)
repetitively activated
responsible for slow, dull, burning pain
What type of transmitters are used by DRG?
Glutamate and Substance P
Where in nerve terminal is glutamate contained?
Found in clear small vesicles
Where in nerve terminal is Substance P found?
dense core vesicles
What causes release of glutamate at nerve terminal? Is release fast or slow?
a single AP; release is fast
What is glutamate responsible for in DRG? Through what type of receptor?
fast synaptic signaling; largely through AMPA receptor
What is required for the release of Substance P from DRG nerve terminals?
repetitive stimulation of C fibers
What is capsaicin?
a member of the TRP (transient receptor potential) family that is specific for temperature
What is hyperalgesia?
with damage, pain pathways become more sensitive to pain (hypersensitivity to pain); occurs after tissue damage
What is allodynia? What is the mechanism of action?
when non-painful stimuli activate nociceptors; C fibers fire repetitively resulting in glutamate release onto spinal cord neurons also activating NMDA receptors
What is thought to be responsible for phantom limb pain?
Allodynia: after amputation C fibers are still "wound up" and could cause changes in the spinal cord
What are the 3 tracts in the anterolateral system?
What is the pathway for the spinothalamic tract?
from laminae I, V, VII to the thalamus VPM and VPL and then up to somatosensory cortex
Do fibers in the spinothalamic tract cross? If so, where?
yes, in the ventral white commissure
Do fibers of the spinoreticular tract cross?
some (has crossed and uncrossed fibers)
Do fibers of the spinomesencephalic tract cross?
What is the pathway for the Spinoreticular tract?
From deeper lamina VII, VIII --> sends off collaterals to synapse in the reticular system of brainstem (pons & medulla) --> then they synapse in thalamus --> to somatosensory cortex
What is the pathway for the spinomesencephalic tract?
from cord laminae I, V to the mesencephalic reticulum, lateral periaqueductal grey matter --> to hypothalamus, limbic system, and midbrain
Which tract in the anterolateral system synapses with other ascending pathways to communicate with other parts of the brain that have to deal with emotion (i.e. amygdala)?
spinomesencephalic tract
Whic tract of the anterolateral system goes directly to the hypothalamus?
What are the 2 nuclei in the thalamus associated with pain?
Lateral and Medial nuclear group
What nuclei make up the lateral nuclear group?
VPL/VPM and posterior nuclei
What entes lateral nuclear group and where does it project?
LNG receives nociceptive specific fibers and projections from the spinothalamic tract; it projects to the primary somatosensory cortex
What makes up the medial nuclear group?
intralaminar nuclei complex (paleospinothalamic)
What inputs does the medial nuclear group receive? Where does the MNG project?
nociceptive specific inputs and projections from the spinoreticulothalamic tract; diffuse projections to the cortex
What are the 3 cortical areas responsible for pain processing?
Anterior insular cortex
Anterior cingulated cortex
Primary somatosensory cortex
What projects to the anterior insular cortex?
What kind of pain info does the AIC process?
medial thalamus;
info about the internal state of the body (autonomic component of pain)
What projects to the anterior cingulated cortex? What kind of pain info does the ACC process?
intralaminar nuclei of medial thalamus;
emotional component of pain
What projects to the primary somatosensory cortex? What kind of pain info does the PSC process?
lateral thalamus (projects to primary then to secondary);
location and intensity of pain (via sensory homonculus)
T/F: There is a conscious and unconscious ability to gate the amount of painful information sent to the cortex.
In the gating hypothesis of pain, which fibers activate the projection neuron and inhibit the inhibitory interneurons (disinhibition)?
C fibers
In the gating hypothesis of pain, which fibers interact with C fibers and may modify the pain signal?
A-beta fibers (carry vibration)
In the gating hypothesis of pain, which fibers decrease the strength of the pain signal?
A-beta fibers
What is the pain path descending from the cortex?
somatosensory cortex --> periaqueductal grey (also receives from hypothal.) --> raphe nuclei --> dorsal horn neurons --> descending neurons terminate on opiod containing cells
What are the transmitters for the locus ceruleus?
raphe nucleus?
spinal cord?
opiod receptor system
At the cellular level, what type of opiod receptors do neurons act on?
pre- and post-synaptic mu type opiod receptors
What is referred pain?
deep nociceptors within viscera can send afferents into dorsal horn where they meet up with various nociceptors from other places such as the skin; the same nerve is stimulated and pain will be experienced froma specific dermatome