Central Mechanism of Pain (7/10/15) Flashcards Preview

Physiology > Central Mechanism of Pain (7/10/15) > Flashcards

Flashcards in Central Mechanism of Pain (7/10/15) Deck (26)
Loading flashcards...
1
Q

What area of the Brainstem is associated with pain?

A

The Caudalis (Medullary dorsal horn) which is the Inferior portion of Medulla. *This is also part of the spinal trigeminal nucleus

2
Q

What Types of neurons do you find in the Medullary Dorsal Horn?

A
You have:
Nociceptive Specific Neurons
- painful mechanical stimuli 
 Wide Range Dynamic Neurons
- Light touch
- Painful mechanical stimuli
- Noxious Heat

*Note: the Nociceptors are usually more restricted to superfical layer of the MDH.

3
Q

Nociceptive specific neurons terminate mostly in ____________ layers of the MDH.

A

Superficial layers I and II

4
Q

Non-nociceptive neurons terminate mostly in _________ layers of the MDH.

A

Deeper layers III, IV and V

*There is overlap in layers II and V

5
Q

Describe Convergence in the MDH. What does it mean? and What happens?

A

Convergence refers to the phenomenon of multiple sensory receptors giving information to a smaller number of neural cells.
In the MDH Convergence leads to the emergence of wide dynamic range neurons.

6
Q

What does the Convergence of peripheral afferent with different receptive fields cause?

A

Well, when you have convergence of cutaneous, joint, muscle and other nerves it can be a substrate for referred pain.
*MDH can be substrate for referred pain.

7
Q

Is Referred pain a normal condition? What (several) factors contribute to it.

A

No! It only occurs under pathological conditions.
These factors can contribute to it:
- Convergence in MDH (Pain and non-pain) afferents converging on “pain-signaling” neuron.
- Peripheral sensitization that occurs with inflammation 7 nerve damage (However, this mostly increases c-fiber sensitivity so it cannot be solely responsible)

8
Q

What is Allodynia?

A

Feeling pain from a stimuli that should not be painful. *One of the 2 characteristics of central sensitization.

9
Q

What is Hyperalgesia?

A

Feel EXCESSIVE pain from a stimuli that shouldn’t have been that painful. *The second of the 2 characteristics of central sensitization

10
Q

What is Central sensitization?

A

Basically, when a stimuli can be either magnified or misconstrued (neurally) to be painful or sometimes both.

11
Q

What evidence do we have that supports Central sensitization?

A

If you inject capsaicin into a hand, pain will be felt at the injection and all around it.

However, if you block the A-delta and A-beta fibers pain is no localized to only where the capsaicin actually is! (Due to C-fibers)

12
Q

Describe the Process of Central sensitization…..

A

First, it begins with a barrage on C-fibers (acute pain or inflammation) this will lead to…
MDH Neuron Responses
- depolarization by substrate P (Tachykinin)
- Modification of NMDA receptors (Removal of Mg++ block)
- Increase in Conductance of NMDA receptor
Which will cause…….
Previously ineffective A-fibers to become effective!
- A-fibers release of glutamate effective at NMDA receptor now = larger receptive field.
- Response to innocuous stimuli induces pain (A-beta fibers)

13
Q

Describe Central sensitization following Pulpitis…..

A

So you have inflamed teeth on one side of your mouth and yet you still have a lower pain threshold in contralateral healthy teeth. Why? B/C the inflamed teeth are “sensitizing” central neurons with input to make Healthy teeth more sensitive!

*This is due to central sensitization and Convergence.

14
Q

Is pain confined to the MDH?

A

No..Trigeminal and pons can play a part too!

15
Q

What is a Trigeminal Tractotomy?

A

Cutting select fiber to the MDH to prevent pain.

16
Q

What are the effects of a trigeminal Tractotomy?

A

If C1-C3 (all afferents) are cut you can expect the following:

  • Loss of thermal and light touch to the back of the head.
  • Normal thermal and touch to face, but no pain.
  • Hypolgesia in intraoral region
  • Pupal pain remains intact!
17
Q

What are the effects of a central lesion in the pons?

A

Diminishes intramural and premolar pain along with intraoral touch and thermal.

18
Q

There are multiple pain pathways, what are the 3 you need to know?

A
  1. Afferents -> MDH -> N. Submedius -> cingulate cortex = emotional experience of pain
  2. Afferents -> MDH -> VPL (Thalamus) -> S1 (cortex) = sensory aspect of pain
  3. Afferents -> MDH -> Pons and Medulla (RF and oral motor Nerve (jaw-opening reflex, increased HR and BP))
19
Q

What is the response to pain/stimuli in the VPM (Not VPL!)?

A
  1. Small receptive field so it’s good at locating “Where” the stimulus is applied.
  2. It tracks the onset/offset of the stimulus so it knows “when” it is applied.
  3. The stimulus creates a linear response here.
20
Q

What is the repose to pain/stimuli in N. Submedius?

A
  1. Larger receptive field so it’s NOT good at locating stimulus precisely.
  2. The response outlasts the stimulus
  3. Neural representation of negative emotion outlasts the stimulus.
21
Q

How does Phantom Pain occur?

A

Phantom pain is due to peripheral changes such as:

  • sprouting
  • Ectopic impulses
  • Ephaptic transmission
  • Up/down regulation of neurotransmitters, channels and transduction molecules

AND Central changes such as:

  • Sprouting
  • central sensitization (unmasking of synapses)
22
Q

The N. Submedius and Cingulate cortex do what?

A

Process the emotional component of pain

*Neural response outlasts the stimulus (Poor localization)

23
Q

The VPL and somatosensory cortex do what?

A
  • Localization of pain (small receptive field)
  • Tracks pain stimulus onset and offset
  • May mediate phantom pain through reorganization
24
Q

How can forebrain bundles modulate pain perception?

A
  • Anxiety can increase pain perception.

- Placebo effect can suppress pain perception.

25
Q

T or F, Anterior cingulate cortex is susceptible to opioids.

A

True!

26
Q

Describe the Descending control of Pain…

A

Multiple CNS sites modulate pain:

  1. Forebrain ant. cingulate cortex = anxiety and placebo effect
  2. Midbrain Periaquaductal grey = pain suppression
  3. Rostral ventromedial medulla
    * Many of these sites contain Endogenous opioids to suppress pain!