Pain- Ross Flashcards
Acute pain is required for survival.
Response to pain has a genetic component: ex _______
red hair feels more cold for any given stimulus
Noxious stimulus=
thermal/mechanical/ chemical
Pain=
somatic superficial
somatic deep
visceral: organ
neuropathic
Sensory unit=
sensory nerve cell body in dorsal root ganglion + its
central to SC and peripheral extensions + its cutaneous and visceral endings
**creates clinical useful maps: somatic sensory: dermatomes (area of sensory information from one dorsal root)
A-alpha and A-beta are both ____
FAST pathways
–signal pressure, stretch and other tissue movements to dorsal columns then somatosensory cortex
Vs A-delta and C pathways–> send from:
from tissue and skin nociceptors to spinothalamic
Peripheral sensory pathway:
peripheral sensory nerve carries _____
sensory afferents fibers
**pain receptors are called: nociceptors
free nerve endings with their cell bodies in the dorsal root ganglia
primary afferents classified by size:
A-beta & A-alpha: fast, light touch
A-delta: carry sharp pain
C fibers= (unmyelinated) slower, dull burn pain
Pain (nociceptor) and stretch receptor’s are present in the skin as well as:
deep somatic and visceral structures
-carried by A delta and c fibers: they respond to heat, cold, intense mechanical distortion, ph changes, application of chemical irritants
nociceptors transmitters are _____
**ATP, serotonin and histamine
- open up sodium channels and propagate depolarization
- when conduction in these peripheral n. is abolished one is unable to detect pain
sensitization: describes how the threshold activation of a nociceptor can be:
- decreased?
- increased?
decreased by chemical mediators such as prostaglandin (easier to feel pain)
- increased by serotonin, thromboxanes and endorphins (harder to feel pain)
- sensitization explains why an innocuous stimuli (light touch) can produce pain (allodynia) or the opposite can occur
SC Pain Pathways Dorsal Horn
-in the SC gray matter of dorsal horn the:
end of afferent n. releases the transmitters glutamate, calcitonin and substance P (neuropeptide)
-ascending pathways: contralateral thalamus then to cortex, frontal lobes (emotional input here: fear and pain)
Convergence theory=**
of referred pain: visceral and somatic afferents converge on same area dorsal root) of sc
ex. MI pain hurts the right arm
Visceral pain** (describe)
-**Vagus carries sensation from esophagus, stomach, small bowel and proximal colon
- *spinoreticulothalamic pathway slower conducting
- -from gut,periosteum and peritoneum
It’s the forebrain ( _______) that sends signals to somatosensory cortex, cingulate cortex and insular cortex. The Cortex interprets the signal of pain (emotional/rational input) and ______
(thalamus)
-modulates it.
Descending pathways:
1. Pain modulation at Cortex SS to thalamus 2. ICortex to PAG 3. to Rvm medulla
Nocireceptive pain signal to thalamus and limb is carried by _____
lateral spinothalamic tract**
the dorsal columns=
fine touch and proprioception, vibration :length and tension (unconscious proprioception) and localization of pain
the posterior spinocerebellar tract=
length and tension of muscle fibers (unconscious proprioception)
Other Descending Pathways
- Areas of limbic forebrain, amygdala and Hypothalmus also project to PAG
- PAG (periaqueductal grey matter) modulates ascending pain transmission through the rostral ventromedial medulla (RVM)
-there is release of endorphins (enkephalin)
endorphins turn on/off cells that inhibit (green) or facilitate control of nociceptive signals (red)
In addition to endorphin connections:
-Noradrenergic=
-Sertonergic=
-locus ceruleus (pons) to sc blocking spinal nociceptive neurons
- medulla to dorsal horn cells
- (rationale to use SSRI)
