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Terms in this set (16)
Perceive pain and temperature
transduction of painful stimuli to conscious awareness
Primary Afferent axons
Aa, Ab, Ad, and C fibers
Aa = proprioception
Ab = mediates touch sensations
Ad + C fibers = mediate pain and temperature
Transducers of noxious sensations, bare nerve endings:
Thermal: >45 and <5, Ad
Mechanical: intense pressure, pinch, tissue crush - via Ad
Polymodal: noxious stimuli, carried by slowly conducting, unmyelinated "C" fibers
Silent (viscera) = chemical or inflammatory response
pain that result form disorders of the PNS or CNS: phantom limb, anesthesia delorosa
Ad = sharp pain, C fibers = burning diffuse radiating nociception
Neurochemistry of Pain
Ad and C fibers secrete glutamate as well as neuropeptides like substance P
Inflammatory response and primary hyperalgesia
bradykinin stimulates pain receptors directly
prostaglandins hyper sensitize nociceptors
substance P induces vasodilation and swell in adjacent tissues - accelerated by histamine from mast cells
burn sensitize nociceptors ->stimulating release of prostaglandins + bradykinin -> stimulating Ad and C fibers increasing prostaglandins
Centrally mediated hyperalgesia
sever injury cause C-fibers to fire repeatedly this causes up-regulation of pain response via NMDA/glutamatergic mechanisms; this pain "memory" is self-reinforcing with increased levels of substance P
Endogenous opiate pathway
1. Neurons from PAG projects to raphe nuclei in medulla. 2. Synapse to enkephalinergic neurons (pre-synaptic to incoming C-fibers) dorsal horn. Enekephaniergic interneurons block incoming C-fibers presynaptically (so you don't feel pain).
hormone produce that blocks incoming nociceptive inputs
Gate control circuit
an interneuron is stimulated by the non-nociceptive afferent and inhibited by the C fiber. The combined effect tends to inhibit principal cell's conveyance of pain signals.
Ascending indirect targets
Reticular formation: attention and vigilance
Intralaminar thalamic nuclei (centromedian): diffuse sensory/motor cortex involvement. attention + arousal
Cingulate - limbic gyrus: vast array of projects
Periaqueductal gray (PAG): autonomic recruitment circuitry.
Visceral + cutaneous nociceptors enters the spinal cord and ascend together. Sometimes they innervate the same neurons in lamina V.
Rexed laminae I,II,IV and V.
I = marginal zone Ad nociceptive-specific, and some wide range
II = substantia gelatinosa - C fibers synapse on interneurons (both excitatory, inhibitory)
IV + V = AB, Ad; wide dynamic range; to the brain stem, various thalamic nuclei. Many nociceptive vesceral afferents
III-V = spinal nucleus proprius
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