Lecture 9 Peripheral + central response to trauma

Question 1

Define pain

Answer 1

unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage
* “need state”

Question 2

Nociception

Answer 2

The neural process of detecting noxious (harmful) stimuli

Question 3

Nociceptors

Answer 3

specialized ‘free’ nerve endings that detect noxious stimuli.

Question 4

Classes of Nociceptors:

Answer 4

1. Thermal
2. Mechanical
3. Polymodal
4. Silent (not active unless inflammation or chem)

Question 5

A-delta

Answer 5

Myelinated
* Small diameter
* “First pain”
* Degree of localisation

Question 6

C fibres

Answer 6

Non-myelinated
* “Second pain”
* Slow and dull
* Polymodal

Question 7

Dorsal Horn Lamina levels and fibres

Answer 7

Transmission of nociceptive input occurs in dorsal horn, spinal cord
* Lamina I and V transmit A-delta
* Lamina I and II transmit C fibres

Question 8

how is noxious info from the orofacial region communciated?

Answer 8

Through the spinal trigeminal nucleus (SpV) in brainstem

Question 9

“Referred pain”

Answer 9

Viscera also project to dorsal horn in similar organisation
* convergence of signal

Question 10

Neurotransmitters that are released when nociceptive N. activate N. in dorsal horn

Answer 10

1. Glutamate
2. Neuropeptides (predominantly in superficial lamina)

Question 11

Lewis’ Triple Response

Answer 11

“retrograde activation” of C-fibres
1. Info > back to cell body
2. Info > back to terminal
3. Release of neuropeptides at the terminals
4. -> Inflammation etc.

Question 12

What does tissue damage trigger?

Answer 12

Local release of chem (Bradykinin, prostaglandins, K+)

Question 13

What does the release of Bradykinin, prostaglandins and K+ do?

Answer 13

Activates nociceptors
1. Retrograde signal to DRG
2. Neuropeptide release
3. Act on mast/blood cells

Question 14

Sensitisation

Answer 14

Occurs after repeated application of noxious mechanical stimuli or inflammation

Question 15

Bidirectional signalling in the nociceptors

Answer 15

Substance P and calcitonin gene-related peptides (CGRP) released from nociceptive nerve endings.
* Histamine release > edema.

Question 16

Evolutionary POV of sensitising

Answer 16

Provides amplification of a warning signal
* Pay attention to the area
* Spread peripheral sensitisation

Question 17

Allodynia

Answer 17

Previously innocuous stimuli are now perceived as painful

Question 18

Hyperalgesia

Answer 18

Noxious stimuli are perceived as more noxious.

Question 19

Growth factor involved in sensitisation signalling

Answer 19

1. Inflammation
2. TNF, IL-1
3. Mast cell
4. NGF
   Go to nociceptive nerve endings

Question 20

Touch and proprioception (innocuous) tract

Answer 20

MEDIAL LEMNISCUS tract
1. A-beta
2. DRG. > Dorsal horn
3. Synapse deep > projects ipsilaterally
4. decussates contralaterally @ dorsal COLUMN
5. Project to thalamus > S1

Question 21

Where does the innocuous stimuli project to within the ventral posterior thalamus

Answer 21

1. VP LATERAL if it’s the body
2. VP MEDIAL if it’s the head

Question 22

Sensory-discriminative tract

Answer 22

SPINOTHALAMIC tract
1. A-delta + C
2. DRG > Dorsal horn
3. Crosses contralaterally in dorsal HORN (ventral commissure)
4. Thalamus > S1

Question 23

What is different about the sensory discriminative tract when the info is coming from the head

Answer 23

Through trigeminal nerve and trigeminal ganglion (as opposed to DRG)

Question 24

Amygdala involvement in pain

Answer 24

Generation of emotional state
* synapse at parabrachial N. (pons) > central amygdala