Pain

Question 1

nociception

Answer 1

• perception of pain
• Requires specialized receptors that can respond to stimuli including:
• • Extreme temperatures (hold and cold)
• • Mechanical stimulation (ie. Stabs, pricks)
• • Chemical stimulation (ie. Acid exposure)

Question 2

nociceptors

Answer 2

• pain receptors (free nerve endings) are activated when a stimulus exceeds a noxious threshold
• classes of pain receptors: A-Delta and C-Fibres
• Neurotransmitters utilized by nociceptive fibers: glutamate, substance P, CGRP

Question 3

A-Delta Fibres

Answer 3

• myelinated
• Localized first “sharp” pain
• Respond to: mechanical (pinching) and thermal (hot/cold extreme)

Question 4

C-Fibres

Answer 4

• unmyelinated
• Mediate the diffuse, poorly localized “second pain”
• Respond to: mechanical, thermal, chemical stimulation

Question 5

pain

Answer 5

• Unpleasant sensory and emotional experience associated with actual or potential tissue damage
• Even in the absence of tissue damage (ie. Psychological causes), can still be described as pain
• Not stimulus-dependant

Question 6

symptoms of pain in animals

Answer 6

• Failure to groom
• Changes in posture/gait
• Decreased food and water intake
• Lethargy/reluctance to move
• Vocalizations
• Failure to interact with conspecifics
• Avoiding or resentment of handling
• Scratching or biting

Question 7

why is pain necessary?

Answer 7

• allows you to use your body correctly without damaging it and modulating what you do
• Necessary for survival
• inability to feel pain can have devastating consequences (ex. Ashlyn Blocker)

Question 8

Ashlyn Blocker

Answer 8

• Can feel:
• • Pressure
• • Distinguish between soft touch and strong touch
• • Temperature: hot and cold
• • Empathy and emotional pain
• • Some types of fear (emotional fear)
• Cannot feel:
• • Extreme temperatures (very hot and very cold)
• • Cannot understand pain in others

Question 9

Congenital insensitivity to pain (CIP)

Answer 9

• class of disorders that make people unable to feel pain
• Dangerous condition – increased risk of: oral cavity damage, fractures, corneal damage
• Individuals with CIP more likely to die during childhood (ie. Injuries, Illnesses, Burns)

Question 10

causes of insensitivity to pain

Answer 10

• gene mutations (family of disorders)
• ex. mutation in gene SCN9A
• • Different mutation: severe pain and chronic pain disorder
• • Encodes a sodium ion channel (local anesthetics likely to work on same channels)
• • This channel highly expressed on nociceptive neurons
• • Important “amplification” channels that contribute to neurons firing action potentials

Question 11

SCN9A knockout studies in mice

Answer 11

Use KO mice - decreased response to mechanical and inflammatory pain

Question 12

pain processing in naked mole rat

Answer 12

• Naked mole rats are pain insensitive (at skin level)
• • Mutation in TrkA likely responsible for pain insensitivity
• • High temperature (in room, water, etc.): caused nerve growth factor (NGF) to bind to TrkA receptor
• • Signal cascade resulting in sensitization/opening of the TRPV1 channel on sensory neurons
• • Sensory neurons fire action potentials: sends info to brain = painful stimulus

Question 13

naked mole rats: does pain insensitivity cause survival disadvantage?

Answer 13

• TrkA mutation: hypo-functional
• Requires 10x more NGF to initiate a response (but not dysfunctional)
• Development: pain receptor (TrkA) numbers are much higher in newborns than adults
• Potential advantages:
• • Help survive in abrasive, hot underground tunnels
• • Energy conservation – low metabolic rate