mechanosensation and pain

Question 1

in Brown sequard syndrome, which side of the body loses pain sensation and which side loses touch sensation?

Answer 1

side same as lesion: touch
side opposite lesion: pain

Question 2

what are the 5 touch receptors and what do they sense?

Answer 2

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

Question 3

what are phasic receptors and neurons?

Answer 3

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

Question 4

what are tonic receptors and neurons?

Answer 4

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

Question 5

what is pain?

Answer 5

an unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage. Protective mechanism

Question 6

what is congenital analgesia?

Answer 6

inability to process pain

Question 7

what are mechanical pain receptors?

Answer 7

responds to mechanical damage (cutting, crushing…)

Question 8

what are thermal pain receptors?

Answer 8

responds to temperature extremes

Question 9

what are polymodal pain receptors?

Answer 9

responds to damaging stimuli

Question 10

what are the 2 types of pain?

Answer 10

fast and slow

Question 11

what is fast pain?

Answer 11

initial perception as brief, sharp sensation that is easily localized – originates from specific mechanical or thermal receptors. Followed by slow throbbing and persistence

Question 12

what is slow pain?

Answer 12

activated by chemicals like bradykinin or prostaglandins. Provoked by stimulating polymodal receptors

Question 13

what are the fibers that transmit pain impulses to the CNS?

Answer 13

Alpha gamma (myelinated, medium sized, fast - cold, warmth, mechanical ) sharp, stabbing
C (unmyelinated, smallest, slowest - heat, cold, mechanical ) burning, throbbing

Question 14

what are the 2 main pain neurotransmitters?

Answer 14

substance P
glutamate

Question 15

what does substance P do?

Answer 15

activates ascending pathways that transmit pain signals for further processing

Question 16

what does glutamate do?

Answer 16

excitatory. Binding to AMPA receptors or NMDA receptors (contributes to hypersensitivity/hyperalgesia)

Question 17

what is chronic pain caused by?

Answer 17

Damage to pain pathways in peripheral nerve or in the CNS processing areas

Question 18

what is sensitization?

Answer 18

pain is perceived due to abnormal signaling

Question 19

what is hyperalgesia?

Answer 19

lowered threshold to the thermal or mechanical stimulation - induced pain at the injured site

Question 20

what is allodynia?

Answer 20

normally innocuous stimulus can result in painful sensation due to sensitization of the adjacent uninjured tissue

Question 21

what is periaqueductal gray matter?

Answer 21

a built in processing system

Question 22

why does rubbing an injury make it feel better?

Answer 22

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