Week 9 - Sensory Processing P2

Question 1

What is pain

Answer 1

an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage

Question 2

What is the difference between acute and chronic pain

Answer 2

acute pain is normally more short term (less than 3-6 months) due to a clear, identifiable injury or illness.

Chronic pain is long term (beyond normal healing time > 3-6 months) and may persist after an injury has healed or without clear cause

Question 3

Information regarding pain is transmitted through what 2 types of nociceptive nerve fibers

Answer 3

• C fibres
• Aδ (A-delta) fibers

Question 4

What are the properties of C fibres

Answer 4

• unmyelinated
• conduction speed is slow
• pain type: dull, burning, aching pain
• stimuli: mechanical, thermal and chemical
  Function: delivers ongoing, longer lasting pain often associated with tissue injury or inflammation
• causes nauseous, chronic pain usually associated with tissue damage and destruction

Question 5

What are A-delta fibers

Answer 5

• thin myelinated
• small diameter
• conduction speed is fast
• pain type: sharp, localized, immediate pain
  Stimuli: mechanical and thermal (e.g. pinprick, burn)
  Function: Alerts you quickly to harmful stimuli so you can react (e.g. pulling hand away from hot surface)

Question 6

What neurotransmitters do nociceptive nerves use

Answer 6

Peptide neurotransmitters (substance P, neurokinin A, CGRP)

• peptides synthesized in ganglia and transported both centrally and peripherally

central release - nociceptive transmission
Peripheral release - neurogenic component of inflammation

Question 7

What do A-delta fibres mainly innervate

Answer 7

• mainly innervates the skin
• not normally associated with deeper structures

Question 8

Where do C-fibres innervate

Answer 8

• associated with skin but also innervate deep tissue and organ systems

Question 9

What is the conduction velocity for A-delta fibres

Answer 9

20m/sec
takes 0.1 sec to send a signal

Question 10

What is the conduction velocity for C fibres

Answer 10

0.5m/sec
3-4 sec to send a signal

Question 11

are A-delta fibres sensitive to pressure and low dose local anesthetics

Answer 11

relatively sensitive to pressure

relatively insensitive to low dose of local anesthetics

Question 12

are C fibres sensitive to inhibition by pressure and low dose local anesthetics

Answer 12

relatively insensitive to inhibition by pressure

sensitive to low does of local anesthetics

Question 13

what happens if you block the activity of A delta fibres in response to a noxious stimulus

Answer 13

you may block the sharp pain but the pain associated with C fibres activation becomes much stronger and more aversive

• Conversely it appears that is AO fibres are active, they may reduce the nociceptive sensations associated with the stimulation of C fibres

Question 14

What is a nociceptive signal

Answer 14

signal sent in the nociceptive nerves

Question 15

what is TRPV1

Answer 15

A receptor protein that is only located on pain sensing neurons in the periphery
It is polymodal and responds to:
- Capsaicin
- Temperature
- H+
- Lipids
- Mechanical stimuli

Question 16

How are nociceptive nerves activated

Answer 16

• Capsaicin stimulates nociceptive C-fibres by acting on a specific receptor/ion channel – TRP vanilloid receptor subtype 1-TRPV1R
• 6-transmembrane cation channel – opening allowing influx of mostly Ca2+ and Na+
• causes membrane depolarisation - if depolarisation reaches certain threshold then it generates an action potential in the nociceptive neuron
• This receptor is responsible for much of the “polymodal” natural of these nerves
• Nociceptive nerve terminals also express receptors for a wide range of mediators including glutamate, GABA, Ach, Serotonin, ATP, bradykinin, noradrenaline, histamine, somatostatin, opioids ect

Question 17

blocking TRPV1 will cause what

Answer 17

specifically block pain but not motor or autonomic acitivty

Question 18

why does pain persist longer after the initial event e.g. injury or infection

Answer 18

because nociceptive nerves are subject to ongoing chemical stimulation

Question 19

what factors ma be responsible for the ongoing chemical stimulation of nociceptive nerves

Answer 19

• various neurotransmitters -serotonin, histamine and acetylcholine
• kinins - 2 peptides, bradykinin and kallidin, are released under conditions of tissue injury -potent pain producing substances
• Metabolic -= lactic acid, K+ ion, H+ ions, ATP and ADP – released by damaged cells and hypoxic tissues