Chemosensation & Pain Flashcards
Gustatory pathway
1st order: CN ganglia (cell bodies) synapse @ solitary nucleus
2nd order: Solitary nucleus synapse @ VPM
3rd order: VPM synapse @ Gustatory Cortex
Olfactory System Tract
bundle of axons connecting the mitral (MAIN OUTPUT cells) and tufted cells of the olfactory bulb to several target regions in the brain, including piriform cortex, amygdala, and entorhinal cortex.
Capsaicin
principle ingrediant responsible for heat in hot peppers
activtes receptors on C-Fibers which normally respond to heat
repeated applicaiton desencitizes pain fibers
4 mechanical primary sensory receptors
Superficial– small receptive fields
1) Meissners (light touch, fast, unmeyelinated)
2) Merkels (2 point discrimination)
Deep– lare receptive fields
3) Ruffinis (SLOW, sustained pressure, slow and large, allow modulation of grip of object)
4) Pacinian (FAST, vibration and pressure)
Referred Pain
pain in one region signifying damage in another
Dorsal Horn neuron in Lamina V recieves affarent signals from viceral nociceptors and cutaneous nocicpetors
Lamina V
recieves input from Alpha-gamma + C-fibers (nociceptive) as well as ABeta
Gate control theaory
larger diameter A-Beta fibers going through lamina inhibit transmission of smaller nerves carrying pain signla.
lamina II
where C-fibers synapse (dorsal horn)
Thalamic Pain syndrome (Dejenrine-Roussy)
chronic pain resulting from lesions in posterior thalamus
first get numbness and then tingling
nociceptive pain fibers
A-delta = fast, thin, myelinated. Carries Afferent info about localized, intense pain C= slow, throbbing, long lasting pain (Glut and Sub P)
Terminate in Dorsal Horn of spinal cord Lamina V (although C fibers synapse at II)
“Wind Up Theory” –Nueropathic pain
repeated activation of NMDA rectpors
causes increased response to same stimulus nerve damage can produce this
C fibers release GLUT and SUB P
stimulus that is usually nonpainful becomes painful (Allodynia)
Anti-inflammatory (NSAIDs
ASA and Ibuprofen
Acetaminophen
blocks TRPV1 (vallinoid receptors) and COX inhibitor no effect on inflammation
Prednisone (glucocorticoid)
inhibits PG and Leukotriene synthesis by acting on hormone receptors (transcription factors)
reduces inflammation
Morphine and Codeine
morphine (moderate to severe)
Codeine (weaker)
ascending pathway– hyperplarizes postynaptic neurons by opening presynaptic K+ channels and close voltage gated Ca2+ channels (inhibits NT release)
Descending pathway: Inhibit GABA actions, disinhibit NT modulating pain in dorsal horn (NE)
Amitriptyline
Monoamine reuptake inhibitor: tricyclic anti-depressant
blocks reputake of serotonin and NE (used for neuropathic pain, no sedation)
Duloxetine
selective NE and serotonin reuptake inhibitor SNRI
used for pain associated iwth cancer and peripheral diabetic neuropathy
gabapentin
pregabalin
carbamazepine
gaba and pre– ion channel modulator. bind to alpha-2-delta- subunit of ca ion channels to block ca ion influx and relase NT, glutamate and sub P. approved for peripheral diabetic neuropathy
carb– blocks voltage gated Na ion channels. for epilepsy and trigeminal neuralgia
lidocaine
blocks neuronal firing– slow rapid firing of voltage gated Na+ ion channels (Na+ channel blocker). can be applied as cream
capsaicin
blocks neuronal firing- stimulates C fibers causing an AP.
Sub P released –> TRPV1. damages nerve endings reducing ability to send pain signals
causes pain but followed by relef from pain for several weeks
Ketamine
blocks glutamate NTs by blocking Ca2+ influx.
Thermal and Pain receptors
Free nerve endings
sense injurious forces,
Proprioception afferent axons
A-alpha (large, myelinated, transpit porpioceptive form skeletal muscles)
