Pain pathway and pharmacology Flashcards
Pain is multifaceted and complex.
Chronic pain affects approximately 20% of the population
Pain is essential to avoid damage/ react to a damaging situation
Emotional pain – grief
Pain is an unpleasant or emotional experience originating in real or potential damaged tissue.
Pain is an unpleasant phenomenon that is uniquely experienced by each individual;
it cannot be adequately defined, identified, or measured by an observer..
Or can it? Scale of 1-10 – often results in over/underestimation
Pain is the number one reason why people visit their GP.
It can interfere with a person’s quality of life and general functioning.
What is pain?
Three hierarchal levels interact, usually to produce a complex picture of pain:
Sensory – discriminative system processes information about the strength, intensity, quality and temporal and spatial aspects of pain.
Motivational - affective system determines the individual´s approach-avoidance behaviours.
Cognitive - evaluative system overlies the individuals learned behaviour concerning the experience of pain. It may block, modulate, or enhance the perception of pain.
Why do we experience pain?
Pain is nature’s unpleasant but crucial way of warning you of danger.
It stops you repeating any action that causes pain.
Touching something painful activates an immediate withdrawal reflex.
How to measure pain?
Classified using a standard 0 (no pain to 10 (worse pain)
Via a mobility assessment – tracking movement
SHAP value measuring pain degree by monitoring facial expression/morphology via AI
(currently a work in progress)
Age and perception of pain
Children and the elderly may experience or express pain differently than adults.
Infants in the first 1 to 2 days of life are less sensitive to pain (or they simply lack the ability to verbalise the pain experience).
A full behavioural response to pain is apparent at 3 to 12 month of life.
Older children, between the ages of 15 and 18 years, tend to have a lower pain threshold than do adults.
Pain threshold tends to increase with ageing (rather than that they feel less pain).
Studies are inconclusive
What happens if you can’t experience pain?
Some people are born with an absence of pain - a very dangerous condition because they do not realise when they have hurt themselves.
“We fear pain, but in developmental terms from being a child to being a young adult, pain is incredibly important to the process of learning how to modulate your physical activity without doing damage to your bodies, and in determining how much risk you take”
See: 16/12/17 ‘The Family that doesn’t feel pain’ BBC News
Due to a novel human pain insensitivity disorder caused by a point mutation in ZFHX2
also see; A Life Without Pain on 20/20
Pain is a protective mechanism
See the film: Painless
SCN9A – codes for a part of the sodium channel NaV-1.7
NaV1.7 sodium channels are found in the pain transmitting nerve cells.
Congenital insensitivity to pain has been linked to at least 13 mutations in the SCN9A gene which produces a non functional protein
Other mutations in the same gene produce other phenotypes – ie more sensitivity to pain (one amino acid change, keeps the channels open longer and increases the pain signals)
Physiology of pain
How pain is transmitted and perceived is complex because of the nature of the fully integrated constantly changing structure of the CNS, and the symphony of chemical mediators, only a fraction of which are understood.
- Pain source
Transduction - Pain messages move through peripheral nerves
and up the spinal cord - Brain interprets the messages as pain
Transmission - Brain sends Chemicals and triggers other responses
Modulation
There are no pain receptors in the brain itself.
Modulation can turn pain up or down.
Sense organs in the skin
Sense Organs in the Skin are located in the dermis transferring external signals from the epidermis to the inner hyperdermis layer.
Thermo- receptors senses heat or cold
Meissner’s corpuscle senses touch
Nociceptors sense pain
Pacinian corpuscle senses pressure
The PNS includes primary sensory neurons, specialised to detect mechanical, thermal or chemical conditions associated with potential tissue damage
Transduction and transmission
Transduction
During this stage, noxious stimuli (with potential to injure tissue) trigger the release of biochemical mediators (prostaglandins, bradykinin, serotonin, histamine) that sensitise nociceptors.
Noxious or painful stimulation also causes movement of ions across cell membrane, which excite nociceptors.
Pain medication can work during this phase by blocking the production of prostaglandin (eg ibuprofen or aspirin) or by decreasing the movements of ions across the cell membrane (eg local anaesthetic such as lidocaine).
Transmission
Signals have to be transmitted to the spine and brain where they are modified before they are ultimately understood or “felt”
Includes three segments:
First segment - pain impulse travels from the peripheral nerve fibres to the spinal cord.
Second segment - transmission from the spinal cord and ascension via spinthalmic tracts, to the brain stem and thalamus.
Third segment - involves transmission of signals between thalamus to the somatic sensory cortex where pain perception occurs
Pain fibres
Pain fibres transmit impulse to spinal cord through fast or slow fibres:
A-delta fibres - small myelinated fibres that transmit sharp pain (fast and brief)
C fibres - small un-myelinated fibres that transmit dull pain or aching pain (long lasting)
Both can be triggered together
Pain is often a “double” sensation as fast pain is transmitted by the A-delta fibres while a second or later, it is transmitted by the C fibre pathway
Opiods
Pain control can take place during this second process. Opioids block the release of neurotransmitters, which stops the pain at the spinal level.
Natural (and also now synthetic available) the most effective pain killers available today
Areas of Sub-Saharan Africa have no access to opioids – such as they would need for childbirth or surgery anaesthetics – illegal opioids could be seized and repurposed for this
Modulation
Often described as “descending system”
Occurs when neurons in the thalamus and brain stem send signals down the dorsal horn of the spinal cord. These descending fibres release substances such as endogenous opioids, serotonin and noradrenaline which inhibit the ascending painful impulses in the dorsal horn.
see diagrams in notes
Response to pain
Response to pain
The body’s response to pain has both physiological and psychological aspects.
The sympathetic nervous system responds, resulting in fight-or-flight response, with noticeable increase in pulse and blood pressure.
The person may hold their breath or have short, shallow breathing.
