Week 1 - Lecture 1 - Pain pathways and modulation Flashcards
What is the ICF model?
International Classification of Functioning, Disability and Health
Identify the different components of the ICF model and explain each component.
- 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
- 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)
Why study pain?
- 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
What is the function of pain?
• Informs the body when something is wrong • A survival mechanism
Pain: An unpleasant sensory and emotional
experience associated with actual or potential
tissue damage
(International Association for the Study of Pain)
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)
What are the four main components of how we understand pain.
Four main components:
1- Transduction (physical injury - nerve response)
2- Transmission
3- Perception (understanding what is happening)
4- Modulation (Transitioning into chronic pain)
What composes the nervous system?
- 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
What are the different types of receptors?
What has free nerve endings?
What has no receptors?
Free nerve endings :
Skin
Bone
Muscles
No receptors in:
Articular cartilage
Synovial membrane
Pericardium - tissue around the heart
Brain tissue
What is an electrical impulse in the nerve?
- 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
The physiology of pain
What is an afferent pathway?
(ascending)
Carry message to the brain for interpretation
What is an efferent pathway?
(descending)
Carry messages from the brain via the spinal cord
What are 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
What are the possible stimulus or sources of pain?
1- Mechanical - Poke, pinch, aggressive compression (ex: slip and fall)
2- Chemical - inflammatory mediators
3- Thermal - extreme heat or cold applied to tissue
- Pain receptors are unable to adapt to repeated stimuli and thus continue to react until stimuli are removed. Ex: let’s say you are putting gas in the car, the smell of gas will kinda go away but that will not happen to pain receptors
- When pain receptors are stimulated electrical impulses are transmitted to the spinal cord along wo afferent fibres
What are the components of the pain pathway?
- Receptors
- Primary afferents, 1st order neurons
- Dorsal horn of the spinal cord
- Ascending fibers, 2nd order neurons
- Thalamus
- Cortex and other brain areas
Explain a primary afferent.
What is the purple line?
What is the blue line?
What is the red line?
PRIMARY AFFERENTS (1st ORDER)
What is the purple line
A beta fibers
What is the blue line
A delta fibers
What is the red line
C fibers
What are the different primary afferents and their respective sizes?
Ab fibers
sensory from cutaneous receptors, non-nociceptive and do not transmit pain
Ad and C fibers sensations of pain and temperature from peripheral nociceptors
What is fast and slow pain?
- A sharp first pain followed by a second dull, aching, longer lasting pain
- First fast pain is transmitted by the myelinated A(delta) fibers
- Second slow pain is transmitted by the unmyelinated C fibers
What is the role of the spinal cord during transmission of signals to the brain?
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. = image on the right
Inhibition of the inhibitory neuron by the C fiber when there is pain = image on the left
What is an ascending fiber of 2nd order?
• 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 the
noxious stimuli
• Unpleasantness and autonomic activation • E.g., fight/flight response, anxiety
80% of your 2nd order neurons = is in the spinothalamic tract = it carries most of our
2 main afferent pathways = spinothalamic tract + spinoreticular tract
Name a few examples of places in the brain where the thalamus is transmitting the signal?
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
Explain the gate control theory.
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
***
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
What is the descending pain control?
- 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 reenforces 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
What is the Neuromatrix theory of pain?
Melzack’s: pain experience
Neuromatrix theory:
Motivational Affective = like the unpleasant of it
Cognitive Evaluative = has to do more with the cognitive state, perhaps different cultural views, is the pain perceived as good or bad
Sensory Discriminative = physiological characteristics of the pain
