Pathophysiology of Pain Flashcards by Grace Dalimonte

Pain definition?

Unpleaseant sensation and emotional experience associated with actual or potential tissue damage, or describes in terms of such damage

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What aspect of pain makes it unique?

Emotional aspect

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Any abnormal sensation described by a patient as unpleasant?

Dyesthesia

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A sensation that is typically described as “pins-and-needles” or “prickling”, but is not notably unpleasant

Paresthesia

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Reduction or loss of pain perception

Analgesia

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Reduced perception of all touch & pain sensation

Anaesthesia

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Decreased sensation and raised threshold to painful stimuli

Hypoalgesia

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Exaggerated pain response from a normally painful stimulus

Hyperalgesia

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Abnormal perception of pain from a normally non-painful mechanical or thermal stimulus

Allodynia

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Exaggerated perception of a touch stimulus

Hyperesthesia

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Burning pain in the distribution of a peripheral nerve

Causalgia

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Pain does not exhibit ______, unlike almost all other perceptions

adaptation

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The CNS regulates _______ and _________ of pain from lower levels, using multiple different molecules and pathways

perception and transmission

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Pain transmission can actually cause ______ in peripheral tissues

inflammation

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What are widely distributed through multiple layers of the skin as well as many visceral organs?

Nociceptors

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Dermal pain description?

sharp or burning

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Skeletal/cardiac muscle pain description?

dull, pressure like pain

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Joints and bone pain description

sharp, dull, achy

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Blood vessel pain description?

dull

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Hollow viscera pain description?

often dull, cramping but can be sharp

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Mesothelial lining pain description?

sharp

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Type of nociceptors: activated by temperatures > 45 C or less than 5 C

Thermal nociceptors

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Type of nociceptor: activated by intense pressure applied to a structure (i.e. skin)

Mechanical nociceptor

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Type of nociceptor: activated by high intensity mechanical, chemical, or thermal stimuli

Polymodal nociceptors

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Type of nociceptors: receptors that are widely distributed through viscera (but can also be found in the skin) that do not normally transmit pain information (only awakened in a setting of continuous damage or pain)

Silent nociceptors

Nociceptors appear to be very similar to what?

Neurons

2 major types of nociceptors?

C fibers and A fibers

Type of fiber: unmyelinated axons with cell body in the dorsal root ganglia

C fibers

fibers responsible for conducting slow pain and thermoception?

C fibers

Fibers responsible for carrying itching sensations

C fibers

Dull, poorly localized pain in large receptive areas is experienced by what fibers?

C fibers

Type of fiber: myelinated axons with cell body in the dorsal root ganglia

A-delta fibers

Fibers responsible for conducting sharp, pricking pain and some thermoception?

A-delta fibers

What are the transient-receptor potential receptors (TRP) capable of recognizing?

- Cold and heat - Low pH and free radicals - Capsaicin

ASIC receptors are responsible for detecting what?

Low pH

Nociceptors also express receptors for molecules released during inflammatory processes such as:

- Prostaglandins (GPCRs) - Bradykinin - Histamine - Substance P - Serotonin, acetylcholine, ATP

Bradykinin can increase the activation of _____, making it more likely _____

TRP; open

Major nociceptive sensory pathway?

Spinothalamic tracts

Where do peripheral afferent pain fibers of both A-delta and C fibers have their cell bodies?

Dorsal root ganglia

Within the spinal cord, many of the thinnest fibers (C) from what?

Discrete bundle - tract of Lissauer

Peripheral afferent fibers usually terminate where?

Same segment as their spinal nerve

The fibres of the spinothalamic tract usually cross over ______ levels superior to where the 1st-order neurons enter the spinal cord

Two or three levels

How does the paleospinothalamic tract travel?

- Fibers ascend in cord more medially - Project through medulla - Synapse in thalamic nuclei or brainstem areas

Where does visceral pain sensation likely ascend?

Along the anterior spinothalamic tract

Where does better-localized skin-associated pain sensation likely ascend?

Lateral spinothalamic tract

Fast pain?

- well-localized, sharp pain - carried by A-delta fibres

Slow pain?

- Poorer-localization, duller - carried by C fibers - Lasts longer

Most famous brainstem area that can cause profound analgesia?

Periaqueductal gray matter

The periaqueductal gray matter tract directly inhibits pain where?

At the spinal level

What is the periaqueductal gray matter tract mediated by?

Opiate receptors

______ and ______ systems from the brainstem project to the spinal cord and activate inhibitory interneurons

Norepinephrine and serotonergic

How do norepinephrine and serotonergic systems activate inhibitory neruons?

Releasing enkephalins that inhibit nociceptor pre-synaptic NT release

Opioid receptor likely responsible for top-down modulation of pain transmission?

mu receptor

Endogenous agonists of opioid receptors?

opiates

What do opiates include?

enkephalins, endorphins, and dynorphins

Opiate peptide sequence?

Tyr-Gly-Gly-Phe

What fibers have higher concentrations of mu opioid receptors?

C fibers

Gate pain theory?

Presence of non-nociceptive stimuli at a similar site/spinal level tends to reduce pain perception

Peripheral tissue damage can result in increase in pain _____ or _______

sensitivity, hyperalgesia

Molecules released at the site of tissue damage or inflammation increase the effectiveness of nociception?

Peripheral sensitization

Synaptic remodelling in the dorsal horn, leading to increased effectiveness of pain transmission?

Central sensitization

In central sensitization, pro-inflammatory cytokines trigger release of what?

Nerve growth factor from mast cells

What does nerve growth factor increase the release of?

BDNF from C fibers

What direction do action potentials move in?

BOTH ways down a pain fiber

Orthodromic?

Periphery -> spinal cord

Antidromic?

Spinal cord -> periphery

Specific substances C fibers release?

Substance P and CGRP

What can cause mast cell degranulation, vasodilation, and edema?

Substance P

What can cause vasodilation?

CGRP

Process that helps us protect a damaged tissue from further damage?

Neurogenic inflammation

What likely makes C fibers transmit impulses for longer periods of time?

Substance P

Why do neuropathies frequently cause neuropathic pain and not just analgesia?

May be related to pain gate theory

Pain perception and mood disorder areas in the CNS?

Amygdala, cingulate gyrus, insular cortex

Deep pain has indefinite boundaries and its location is ______ from the damaged visceral structure

distant