Mechanisms of Pain Processing
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- Created by: amazingemilyjones
- Created on: 07-04-19 20:54
Mechanisms of Pain Processing
Mechanisms of Pain Processing
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Pain Perception
- The sensation of pain is increased by:
- Discomfort, fatigue, fear, safness, boredom, insomnia, anxiety, anger, depression, loneliness
- The sensation of pain decreased by:
- Sleep, sympathy, companionship, rest, understanding, diversional activities, antidepressants (if appropriate)
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Definitions
- Pain threshold (pain perception threshold)
- the point at which pain begins to be felt
- Pain tolerance level
- the greatest level of pain that a subject is able to tolerate
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Pain Sensation
- Pain sensation originates from specific nociceptors
- Pain can follow injury or occur spontaneously in the CNS (Central Nervous System)
- Chemicals released when there is tissue injury activate nociceptors in the skin, e.g. bradykinin, histamine, 5-HT (serotonin), and inflammatory mediators
- These project into the CNS
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Fast and Slow Pain
- Fast/first pain - small myelinated Ad fibres
- Usually transient, a sensation of sharp, well-localised pain
- Triggers reflex to move away from source of pain
- Slow/second pain - non-myelinated C fibres
- Less easily localised low conduction velocities cause a dull burning pain
- Evokes autonomic responses such as elevated heart rate/blood pressure/sweating
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Pain Levels
Pain is generated at 3 different levels:
- Nociception - peripheral activation and release of pain mediators
- Primary nociceptors, C and Ad fibres
- Pain gating - dorsal horn of the spinal cord
- Ascending and descending secondary fibres
- Pain perception - the brain (thalamus, limbic and cortical systems)
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Influences on Pain
- Pain pathways can be influenced by other events to change the sensation
- Pain receptors are located near touch receptors
- Electrical activation of these receptors can also help (Transcutaneous Electrical Nerve Stimulation)
- Stress or adrenaline can reduce pain sensation
- Descending pathways are activated by these processes that send inhibitory signals
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Pain Sensation
- Pain is sensed by chemical messengers activating peripheral nerves
- Pain is distinguished from other sorts of mechanical and thermal receptors by their higher threshold, since they are normally activated only by stimuli of noxious intensity
- Noxious stimulus: a noxious stimulus is one that is potentially or actually damaging to body tissue
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Types of Pain
Acute
- Usually rapid onset
- Usually identifiable cause
- Limited duration
- Tends to get better
- Biological significance
Chronic
- Not necessarily an identifiable cause
- Large emotional component
- Unpredictable duration
- Does not get better
- None/negative meaning
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Origin
- Nociceptive - stimulation of receptors that respond to heat, vibration, stretch and chemical stimuli released from damaged cells
- Somatic (e.g. rheumatoid arthritis) or visceral (NSAIDs, weak/strong opioids)
- Non-nociceptive/neruopathic - from within peripheral and central nervous system. No specific receptors, but nerve cell dysfunction
- Central or peripheral (e.g. diabetic neuropathy, trigeminal neuralgia)
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Somatic Pain
- Source - nerves that detect somatic pain are located in the skin and deep tissues
- Receptors - these specialised nerves, called nociceptors, pick up sensations related to temperature, vibration and swelling in the skin, joints and muscles
- Characteristics - sharp, well-localised
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Visceral Pain
- Source - internal organs of main body cavities, e.g. heart, lungs, liver, kidney, bladder, ovaries
- Receptors activated - receptors for stretch, inflammation and oxygen starvation
- Characteristics - poorly localised, vague deep ache
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Neuropathic Pain
- Source - from within the nervous system itself - peripheral or central nervous system
- Receptors activated - no specific receptors, nerve becomes injured and becomes electrically unstable, firing off signals at random
- Characteristics - signals interpreted as pain, hypersensitivity, tingling, numbness and weakness
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Examples of Pain
- Somatic - tension headache, osteoarthritis, toothache, sprained ankle, sore throat, burn
- Visceral - colic, angina, appendicitis, peritonitis, pleuritis, irritable bowel sydrome
- Neuropathic - phantom limb pain, trigeminal neuralgia, sciatica, shingles
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