Peripheral Mechanisms of Pain Flashcards
(26 cards)
What is pain?
Unpleasant sensory and emotional experience associated with tissue damage
What class of receptor are all nocicpetors?
free nerve endings
What are A-delta mechanosensitive nociceptors?
Activated by noxious mechanical stimulation
Whare are A-delta mechanothermal nociceptors?
Activated by both noxious mechanical and thermal stimulation
What are C fibers?
Activated by a variety of chemical stimuli in addition to noxious mechanical and thermal stimulation
When they respond to all three, they are also called polymodal nociceptors
What is the difference between an activator and a sensitizer?
Activators are capable of directly activating nociceptors
Sensitizers are capable of lowering the threshold for nociceptor activation
What are four activators of nociceptors?
Potassium
Serotonin
Bradykinin
Histamine
What are four sensitizers of nociceptors?
Prostaglandins
Leukotrienes
Substance P
Calcitonin gene-related peptide (CGRP)
What does the response of a nociceptor depend on?
The type of receptor proteins contained in their peripheral endings
What is the axon reflex?
Activation of one nociceptor ending initiates action potentials that propagate antidromically to invade nociceptor endings which were not activated by the noxious stimulus
What do axon terminals of nociceptors release?
Glutamate
Many also co-release either Substance P or CGRP
What is hyperalgesia?
Increase in pain response to normally painful stimulation
What is primary hyperalgesia caused by?
Occurs in tissue surrounding the site of injury
Caused by peripheral release of chemical activators and sensitizers during the axon reflex
What is secondary hyperalgesia caused by?
Occurs in the area surrounding the area of primary hyperalgesia
Mediated centrally in spinal cord and brain through multiple processes
What is spontaneous pain?
Pain in the absence of any apparent stimulation
What is allodynia?
Sensation of pain resulting from stimuli which are not normally capable of evoking pain
What is acute pain?
Short duration and resolves with healing of damaged tissue
What is chronic pain?
Pain that lasts longer than the time required for normal healing
Clinical definitions are given as fixed times
What is neuropathic pain?
Caused by damage or dysfunction in any part of the peripheral or central nervous system
What is caused by trauma to a peripheral nerve?
A traumatic neuroma is formed by proliferating Schwann cells and axon sprouts attempting to regrow
What are ectopic discharges?
Action potentials generated at an abnormal location
Can be generated by axons in a neuroma
What channel changes occur due to peripheral nerve injury?
Abnormally increased expression of voltage-gated sodium channels in the neuroma and cell body - contribute to ectopic discharges
Increased TRP channel expression in nociceptors
What are Cyclo-oxygenase inhibitors?
Inhibit the formation of prostaglandins, reducing the production of painful chemical stimuli
How do corticosteriods relieve pain?
Reducing inflammation, thereby reducing the amount of activators and sensitizers produced
