Chapter One - Pain and Pathway Flashcards by Myriam Richard

Describe the ICF model.

What is the anatomy telling me, what is the patient telling me… if ever we’re stuck, go back to the ICF Model

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Explain the meaning of these terms: body structures, body functions, impairments, activity (limitations), participation (restrictions)

BODY STRUCTURES – anatomical parts of the body
BODY FUNCTIONS – physiological functions of the body
IMPAIRMENTS – problems in body structure or function
ACTIVITY (limitations) – task or action at the level of the individual
PARTICIPATION (restrictions) – involvement in life situations

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Explain the meaning of these terms: personal factors, environmental factors, functioning, disability.

PERSONAL FACTORS – factors within a person
ENVIRONMENTAL FACTORS – physical, social, attitude
FUNCTIONING – the interaction among the components of the model that contribute to the overall ability to function (positive aspects)
DISABILITY – the interaction among the components of the model that limit the person’s ability to function (negative aspects)

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Why study pain?

(class notes)

A primary reason for people to seek medical attention

Understand the physiology of pain for context or background

Understand the complexities of pain and how it has an impact on our patient’s lives

(answers from students)

So we can understand and treat it

So we can find the root cause (puzzle), what’s the source? Is it the same from one patient to another?

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What is the function of pain?

Informs the body when something is wrong
A survival mechanism

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What is pain?

Pain: An unpleasant sensory and emotional experience associated with actual or potential tissue damage

(International Association for the Study of Pain)

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How do we understand pain?

Something happens somewhere in the periphery, the signal goes to the brain, we process that signal and then there is a response (either physical or emotional)

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What are the four main components of the pain pathway?

Four main components:

1- Transduction (physical injury - nerve response)

2- Transmission

3- Perception (understanding what is happening)

4- Modulation (Transitioning into chronic pain)

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What makes up the CNS and the PNS?

Central Nervous System:

Brain and Spinal Cord

Peripheral Nervous System:

Nerve fibers that are all over the body sending signals to the different tissues and to the CNS

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What is the purpose of receptors? Where do we find receptors? Where is there no receptors?

Receptors : somehow we have to feel the pain

Free nerve endings :

Skin

Bone

Muscles

No receptors in:

Articular cartilage

Synovial membrane

Pericardium - tissue around the heart

Brain tissue

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What is an action potential?

Action Potential: signals move along a nerve process (axon) as a wave of membrane depolarization (more negative)

Rapid transitions between negative and positive electrical potentials

The action potential moves along the axon to the nerve ending where it releases chemicals

All we need to know is on that slide, don’t need to know the details

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What are the two pathways necessary for pain to happen?

Afferent pathways (ascending):

Carry message to the brain for interpretation

Efferent pathways (descending)

Carry messages from the brain via the spinal cord

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What are nociceptors? What are their roles?

Nociceptors
• Receptors that activate the afferent pathways• Unevenly distributed in the muscles, tendons,

subcutaneous tissue and the skin

NOCICEPTORS are sensitive and respond to noxious stimuli stimuli that can cause tissue damage or when tissue damage has taken place
Response to extremes of mechanical, chemical and thermal stimuli• E.g., cuts, burns, sprains

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What are the three stimuli or sources of pain?

Mechanical

Chemical

Thermal

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How are pain receptors different that others? How do they produce pain?

Pain receptors are unable to adapt to repeated stimuli and thus continue to react until stimuli are removed

When pain receptors are stimulated electrical impulses are transmitted to the spinal cord along wo afferent fibres

Impulses travel up the spinal cord to the brain

In the brain, the cortex interprets the impulses as pain and identifies the location

and qualities of pain

Endorphins and enkephalins, natural opioid-like substances• Block transmission of painful impulses to the brain

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What is the pain pathway?

Pain pathway

Receptors

Primary afferents, 1st order neurons

Dorsal horn of spinal cord

Ascending fibers, 2nd order neurons

Thalamus

Cortex and other brain areas

What are the three types of primary afferent (first order) fibers, and what are their respective roles?

A-beta fibers: sensory from cutaneous receptors, non-nociceptive and do not transmit pain

A-delta and C fibers: Sensations of pain and temperature from peripheral nociceptors

What is the difference between fast and slow pain (in types of fibers)?

First fast pain is transmitted by the myelinated A(delta) fibers

Second slow pain is transmitted by the unmyelinated C fibers

What is the purple line?

What is the blue line?

What is the red line?

What is the purple line

A beta fibers

What is the blue line

A delta fibers

What is the red line

C fibers

How can the spinal cord affect the pain signal?

The spinal cord is more than a junction area for transmission of signals to the brain. There are spinal neural circuits, which can alter signal transmission.

C fiber .. our bodies have these sort of safety mechanisms so that we aren’t in a painful stimulus all the time.

Inhibition of the inhibitory neuron by the C fiber when there is pain

What is the role of 2nd order neurons? What different types of assessing pathways/regions do we find related to pain?

80% of your 2nd order neurons = is in the spinothalamic tract = it carries most of our

2 main afferent pathways = spinothalamic tract + spinoreticular tract

2nd order neurons

Nociceptive signals are sent to the spinal cord and then to different parts of the brain where sensation of pain is processed

There are a pathways/regions for assessing the:

Location, intensity, and quality of thenoxious stimuli
Unpleasantness and autonomic activation
E.g., fight/flight response, anxiety

What is the thalamus? What is the role of the thalamus?

The Thalamus is a relay station
2nd order neurons synapse here
Sends signals (3rd order neurons) to higher brain regions

Thalamus : accepts info and shoots it up to the rest of the brain (via third-order neurons)

Name some parts of the cortex and other brain areas where the pain information might be transmitting.

Some examples of where this information might be transmitting.

Amygdala: fear response

Somatic sensory: location, type (hot cold sharp), quality of the pain

Insular cortex: emotional response of pain (sad)- based on the other aspects will respond

How can pain perception vary from person to person?

Objective and subjective aspects of injury and pain are DIFFERENT!

Despite similar injury, people can differ in how much pain they feel

Depending on the context, pain may not be felt despite injury

Suggests that a physiological mechanism controls the transmission of nociceptive signals to the brain or modifies the interpretation of pain

What do you do when you think something painful is about to happen? What is this reaction called?

Flinch away from it Tense up Rubbing it Why do we do that? It’s maybe a distraction, your changing some sensory input into your body (override that painful experience) It's called MODULATION

Name and describe briefly the three models of pain experience.

Gate control theory Blocking ascending pathway Descending Pain Control Expands on Gate Control theory with input from higher brain centers Endogenous opioids Nociceptors to stimulate the release of endorphins, bind to block pathway

How does the gate control theory work?

The concept of the gate control theory is that non-painful input closes the gates to painful input Ascending Aβ fibers block pain impulses at the spinal cord level carried along Aδ and C fibers Results in prevention of the pain sensation from traveling to the central nervous system

In the gate control theory, describe the actions of the large diameter fibers and the small diameter fibers. Give one example.

(L) Large diameter, myelinated (fast– can beat pain)• Stimulates projection cell (P) •Stimulates inhibitory neuron (i) (S) Small diameter, myelinated/unmyelinated (pain)• Stimulates projection cell (P) • Inhibits inhibitory neuron (i) * Occurs whether or not signal reaches brain (top) * E.g., rub thumb after hitting it with a hammer Inhibitory neuron = Little yellow i = is always on and is making sure that the non-painful input closes the gates to painful input A-beta neuron = L in green Large fiber travels faster than a small fiber = which allows to essentially

Blocking ascending pathway Ascending Aβ fibers block pain impulses at the spinal cord level carried along Aδ and C fibers Results in prevention of the pain sensation from traveling to the central nervous system What is the name of this theory?

Gate control theory

Descending pain control

Describe the descending pain control theory.

Activity from descending fibers (e.g., PAG) project to the dorsal horn and could also modulate this gate (inhibit/facilitate) Nociceptive information reaches a threshold that exceeds the inhibition elicited It “opens the gate” and activates pathways that lead to the experience of pain and its related behaviors. Trying to block the signal in getting to that second order neuron, in addition to the gate control theory Inhibition of the signal but the signal continues and is too strong (and we can’t override it), it can override the descending pathways and that reinforces the urge to, for example, move your hand Abnormality in this system can lead to chronic pain : the pain is not inhibited. Lots of different ways that can happen

Internally produced molecules with opioid-like action to regulate transmission of nociceptive signals Similar brain regions that modulate the signal from nociceptive afferents. What is this theory?

Endogenous opioids

Describe the endogenous opioids theory.

The brain releases endogenous opioids in response to pain perception Internally produced molecules with opioid-like action to regulate transmission of nociceptive signals Similar brain regions that modulate the signal from nociceptive afferents Distribution varies by endogenous opioid family

What are the three classes of endogenous opioids?

Three classes: Enkephalins Endorphins Dynorphins

What is the endogenous opioids theory? What is one aspect to consider?

* Inhibitory effect on nociception * Slower but has a longer lasting effect * We naturally express the receptors for these molecules thus allowing the chemical to bind for a long period of time • Relies on circulation of chemical versus action potential along neurons• E.g., prescribe ROM (within a pain free range) Produced by the same brain regions and that there are these 3 classes that exist = is what you need to know Don’t have to know the details, how they function or where they come from Bad circulation = these will not function as well, because they won’t get to the root of the problem(increasing circulation = better) Prescribing simple ROM (range of motion)= will increase blood flow and also increase the release of those natural opioids

What is the Neuromatrix Theory (Melzack's: Pain Experience)

Neuromatrix theory: A) Motivational Affective = like the unpleasant of it B) Cognitive Evaluative = has to do more with the cognitive state, perhaps different cultural views, is the pain perceived as good or bad C) Sensory Discriminative = physiological characteristics of the pain