Pain Physiology Flashcards
Pain definition
an unpleasant sensory & emotional experience associated with actual or potential tissue damage (A PERSPECTIVE)
is whatever the experiencing person says it is
may not be directly proportional to amount of tissue injury
highly SUBJECTIVE, leading to undertreatment
What does pain do?
amplifies the body’s stress response to traumatic injury (pain helps you to stop moving typ.)
causes endocrine & metabolic abnormalities
impedes a patient’s recovery from trauma & surgery
Acute pain:
lasts less than 6 months, subsides once the healing process is accomplished
Chronic pain:
involves complex processes and pathology. Usually involves altered anatomy and neural pathways. It is constant and prolonged, lasting longer than 6 months, and sometimes, for life.
Why treat pain?
Tissue damage has the potential to elicit mechanisms that can create disabling, refractory, chronic situations that may prolong and even outlast the period of healing.
What is the Pain Theory?
Cousins’ Theory of Pathophysiology of Acute Pain
Severe, unrelieved acute pain results in abnormality enhanced physiological responses that lead to pronounced & progressively increasing pathophys
↑ Pathophysiology –> ↑ significant organ dysfunction –> ↑ morbidity & mortality
What are harmful effects?
Cardiovascular and respiratory systems are significantly affected by the pathophysiology of pain
- adrenergic stimulation (↑ SNS)
- hypercoagulation, leading to DIC
- ↑ heart rate
- ↑ CO
- ↑ myocardial O2 consumption
What is the pathophys of pain?
- ↓ pulmonary vital capacity (↓ lung function)
- ↓ alveolar ventilation
- ↓ functional residual capacity
- arterial hypoxemia
- suppression of immune functions, predisposing trauma patients to wound infections & sepsis
What is Chronic Pain Syndrome?
- Pain becomes focus of life
- Relationships become altered
- Sometimes the result of acute, unrelieved pain - such as multiple trauma, phantom limb pain after amputation, repeated back surgeries
- sometimes stems from neuro-muscular disorders such as fibromyalgia, rheumatoid arthritis, MS
What are the Pain pathways?
- Specialized receptors = free nerve endings (that only send pain signals if they’re damaged in any way)
- Stimulation
– mechanical damage
– extreme temp
– chemical irritation - 2 types of neurons
– A-delta: 1st pain, sharp
– C: 2nd pain, dull - 4 distinct processes
– transduction, transmission, modulation, perception
What are the 4 processes to pain?
- Transduction
- Transmission
- Perception
- Modulation
Transduction:
Local biochemical changes in nerve endings that generate a signal
Transmission:
Movement of that signal from the site of pain to the spinal cord and brain
Perception:
Synthesis & analysis in the brain
Modulation:
Endogenous systems in place that can inhibit pain at any point along the pathway
What are Nociceptors?
free nerve endings with the capacity to distinguish between noxious and innocuous stimuli. When exposed to mechanical (incision or tumor growth), thermal (burn), or chemical (toxic substance) stimuli, tissue damage occurs. Substances are released by the damaged tissue which facilitates the movement of pain impulse to the spinal cord.
The primary known substances released from the traumatized tissue are:
- Bradykinin
- Serotonin
- Substance P
- Histamine
- Prostaglandin
*Cause cell depolarization by Na+ flux
What is an example of a drug link?
Non-steroidal anti-inflammatories (NSAIDS), such as ibuprofen, are effective in minimizing pain b/c they minimize the effects of these substances released, especially prostaglandins
Cortiosteroids, such as dexamethasone used for cancer pain, also interferes with the production of prostaglandins
What is Transmission?
Impulse –> SC –> Brain stem –> Thalamus –> central structures of brain –> pain is processed
NT’s are needed to continue the pain impulse from the SC to the brain - opioids (narcotics) are effective analgesics b/c they block the release of NT’s
Pain nerve fibers -
fast pain & slow pain
Pain nerve fibers - fast pain & slow pain
From the pain receptors, the pain stimulus is transmitted through peripheral nerves to the spinal cord and from there to the brain. This happens through two different types of nerves fibers:
- A-delta “fast pain” & (protective pain)
- C-fibers “slow pain” nerve fibers (learning & behavioural modification)
What is Fast Pain?
- nerves are called A-delta fibers
- relatively thick size nerve fibers allow the pain stimulus to be transferred very fast (at a speed of 5 to 30 m/sec), hence the name
- this is all to make the body withdraw immediately from the painful & harmful stimulus, in order to avoid further damage
What is Slow Pain?
- starts immediately after the fast pain
- is transmitted by the v. thin nerve fibers, called C-nerve fibers
- pain impulse can only be transmitted slowly to the brain, at a speed of less than 2 m/sec
- body response - immobilization (guarding, spasm or rigidity), so that healing can take place
What is Perception?
- The end result of the neural activity of pain transmission
- It is believed pain perception occurs in the cortical structures - behavioral strategies and therapy can be applied to reduce pain. Brain can accommodate a limited # of signals - distraction, imagery, relaxation signals may get through the gate, leaving limited signals (such as pain) to be transmitted to the higher structures)
What is High Pain Tolerance?
will feel pain, have physiological response to it, but be able to deal with it emotionally (tolerate it - tough ppl)
What is a High Pain Threshold?
for a given amount of damage, the person doesn’t feel that much pain
- body won’t respond - won’t have same adrenal/stress response b/c they’re not feeling the pain but other’s normally would
Perception takes place in the…
somatosensory cortex, cingulate cortex
- sensory discrimination
- emotional response
(no pain until it hits your brain)
What is the Higher vertebrates perception?
- Anatomical components for perception of pain
- From the last third of embryonic development
What is the Primitive vertebrates perception?
- Fish, reptiles, amphibians
- avoidance or escape behaviour
- poorly developed cerebral cortex
What is Modulation?
- Changing or inhibiting pain impulses in the descending tract
(brain → spinal cord) - Descending fibers also release substances referred to as endogenous opioids or endorphins which have the capability of inhibiting the transmission of noxious stimuli. Helps explain wide variations of pain among ppl
- Cancer pain responds to antidepressants which interfere with the reuptake of serotonin & NE which increases their availability to inhibit noxious stimuli
Where do opioids work?
in all systems of pain modulation
- incl. your emotional response & anxiety to it
- not a NT itself, but modulates NT’s & increase/decrease nerve activity
What are Natural Opioids?
Endorphins
- released from their storage areas in the brain when a pain impulse reaches the brain,
- bind to receptors in the pain pathway to block transmission and perception of pain. (inhibit)
Where do Opiates excite cells?
- Midbrain
- Medulla
- Spinal Cord
(PAG - Periaqueductal gray matter)
What activates descending pain modulation system?
increase inhibition of pain
- STRESS!
- fear
- hunger
- thirst
- fatigue
- prolonged motor activity (ex: treadmill can help)
- hypnosis (like placebo)
What are the categories of pain?
Nociceptic
- injury, trauma, infection (normal pain)
Neuropathic
- damage or dysfunction of the peripheral or CNS
Visceral
- arising from an internal organ - myocardial infraction, appendicitis, small bowel obstruction (*IT’S AMPLIFICATION OF PAIN!)
What is apart of Nociceptive Pain?
- Postoperative pain
- Mechanical low back pain
What is apart of Mixed Type Pain?
- Arthritis
- Postherpetic neuralgia
- Sports/exercise injuries
- Neuropathic low back pain
What is apart of Neuropathic Pain?
- Trigeminal neuralgia
- Polyneuropathy (diabetic, HIV)
Neuropathic Pain:
“initiated or caused by a primary lesion or dysfunction in the nervous system”
- feels like burning or electric shock (on fire)
ex: diabetic neuropathy will have this constantly
Hyperalgesia:
intense pain in response to mildly painful stimulus (pinprick)
Allodynia:
pain in response to completely innocuous stimulus (touch)
ex: sunburn
What is Neuropathic Pain?
- Abnormal processing of the impulses either by the peripheral or CNS
- May be caused by injury (amputation & subsequent phantom limb pain), scar tissue from surgery (back surgery high risk), nerve entrapment (carpal tunnel), or damaged nerves (diabetic neuropathy)
- Unclear why depolarization & transmission of pain impulse are spontaneous & repetitive
