mechanosensation and pain Flashcards
in Brown sequard syndrome, which side of the body loses pain sensation and which side loses touch sensation?
side same as lesion: touch
side opposite lesion: pain
what are the 5 touch receptors and what do they sense?
Pacinian corpuscle: vibration/pressure, large
Meissner’s corpuscle: touch, small
Merkle’s disc: touch, small
Ruffini’s ending: stretch, large
Free nerve ending: pain, temperature
what are phasic receptors and neurons?
respond with a burst of activity when the stimulus is first applied, but then quickly decrease their firing rate as the stimulus is maintained - often also exhibit an off response
what are tonic receptors and neurons?
produce a relatively constant rate of depolarization and firing as long as the stimulus is maintained
Touch receptors are the most common receptors in the body
what is pain?
an unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage. Protective mechanism
what is congenital analgesia?
inability to process pain
what are mechanical pain receptors?
responds to mechanical damage (cutting, crushing…)
what are thermal pain receptors?
responds to temperature extremes
what are polymodal pain receptors?
responds to damaging stimuli
what are the 2 types of pain?
fast and slow
what is fast pain?
initial perception as brief, sharp sensation that is easily localized – originates from specific mechanical or thermal receptors. Followed by slow throbbing and persistence
what is slow pain?
activated by chemicals like bradykinin or prostaglandins. Provoked by stimulating polymodal receptors
what are the fibers that transmit pain impulses to the CNS?
Alpha gamma (myelinated, medium sized, fast - cold, warmth, mechanical ) sharp, stabbing
C (unmyelinated, smallest, slowest - heat, cold, mechanical ) burning, throbbing
what are the 2 main pain neurotransmitters?
substance P
glutamate
what does substance P do?
activates ascending pathways that transmit pain signals for further processing
what does glutamate do?
excitatory. Binding to AMPA receptors or NMDA receptors (contributes to hypersensitivity/hyperalgesia)
what is chronic pain caused by?
Damage to pain pathways in peripheral nerve or in the CNS processing areas
what is sensitization?
pain is perceived due to abnormal signaling
what is hyperalgesia?
lowered threshold to the thermal or mechanical stimulation - induced pain at the injured site
what is allodynia?
normally innocuous stimulus can result in painful sensation due to sensitization of the adjacent uninjured tissue
what is periaqueductal gray matter?
a built in processing system
why does rubbing an injury make it feel better?
alpha - beta afferent fibers that carry mechanosensitive information can act to block pain transmission. The terminals synapse on inhibitory interneurons and enhance the inhibitory activity of these interneurons while C fibers inhibit them. If simultaneous information from alpha-beta and C fibers reaches the inhibitory interneurons, then the outcome is an integrated response that provides partial inhibition of the ascending pathway. Lesslend perception of pain
