Neurophysiology - L11 Flashcards
Types of Nociceptors
Fast Stinging - Called Epicritic Pain
Slow Burning - Protopathic Pain
Nociceptor characteristics
Usually unmyelinated, or lightly myelinated
multibranched
respond to noxious stimulis
have a large threshold of activation
Classes of Nocireceptors (3)
Mechanical - respond to crushing pressure
Thermal - Respond to high and low temperature
Polymodal - Respond to both thermal and mechanical
Sensitization
Lowering of the threshold for pain so you feel more pain (think of touching a sunburn)
Process of Sensitization
After a painful experience prostoglandins are released sensitizing all classes of nociceptors. This depolarization of free nerve endings causes release of substance P which further sensitizes ( as well as dilates blood vessels)
Different reactants involved in sensitization
histamine, serotonin release from mast cells dilating blood vessels
bradykinin potassium and prostaglandin depolarize nerve release substance P to dilate blood
Mid-brain PAG -NRM System
Modulate pain sensation within the brain. When you electrically stimulate this area the person will not feel pain
Wide Dynamic range Neuron (WDR)
In spinal cord.
called this because it receives multiple signal (Substance P, HT-5 and such)
Process of Minimizing pain from the Descending pathway
1) substance P excites lamina V
2) travels up to PAG through anterolateral system, and spinal merencephalic fibers
3) PAG causes Enkephalin to be released
4) Which inhibits inhibotors of serotonin in the NRM (disinhibits) (serotonin is normally kept inhibited by tonic discharge)
5) Serotonin 5-HT goes to release Enkephalin within pain fibers resulting in block of substance P on the lamina 5
This is called post-synaptic inhibition
Mechanism of Opiates
Act on Kappa Nu and Delta receptors
Act on G proteins to
1) Block VGCaC
2) Activate K efflux (limits action potential)
3) Inhibit AC thus lowering cAMP
All lower calcium
which thus blocks release of NT substance P to LV
