Pain Patho Flashcards
Gate control Theory
Pathophysiology
Substantia gellatinosa in posterior horn spinal cord
- gate, open, partially open, closed
- A beta fibres converge and decrease nociceptive signal from a delta (somatic nociceptive pain) and C delta (visceral nociceptive pain)
- CNS efferent nerves converge and increase or decrease signal
Pain
Definition
Whenever
whatever
person says it is
subjective
actual or potential tissue damage
3 types of pain
- acute (nociceptive)
- chronic
- neuropathic
Acute pain
Definition
Nociceptor
- sensory neuron transducts pain signal
Nociceptive pain
- pain to tissue injury or potential injury
- most common type of acut epain
- time limited
- stops when inflammatory mediators are cleared
- vital sign changes
3 types of nociceptive pain
- Somatic pain
- visceral pain
- referred pain
Somatic pain
Defintion
Nociceptive pain
bones, connective tissues, skin
superficial or deep
a delta fibres - sharp, localized, acute
c delta fibres - dull, aching
visceral pain
Definition
nociceptive pain
organs and lining of organs
c delta fibres: dull, aching, continuous
can cause hypotensive shock
A delta vs. C delta fibres
A delta
- fast
- large diameter
- myelinated
- sharp localized pain
- somatic nociceptive pain
C delta fibres
- slow
- small diameter
- unmyelinated
- diffuse poorly localized pain
- somatic or visceral pain
- dull aching pain
Referred pain
Definition
Type of nociceptive pain
skin afferent neurons converge on the same interneuron in the posterior dorsal horn as the visceral nociceptor
number skin receptors > number visceral nociceptor
brain interprets location of pain as the skin (distant) from the actual site
Purpose of acute nociceptiv epain
- quickly withdraw from stimuli
- learn form it
- rest the area
Chronic pain
Definition
Pain persists past time of expected healing
> 3 months - 6 months = chronic pain
out of proportion to the injury experienced
Chronic pain
Pathophysiology
healing resulted in change in pain pathway (PNS and CNS)
- hypersensitivity of the nociceptors (lower threshold for activation)
- decreased modulation of pain signal in the spinal cord
Chronic pain
Negative effects
- depresison
- stress
- decreased healing
- mobility
- chronically active stress reposnse
- imparied cognition, learning, memory, fatigue
- no change in VS (adaptive SNS no response)
Neuropathic pain
Definition
injury to nervous system
altered sensory interpretation post healing
Paraesthesia - electrical, numb, tingling, burning, lancing, shooting
occurs with or without stimuli (spontnaeously generated)
hyperalgesia - intesity of pain increased
allodynia - painless stimuli causes pain
dysathesia - painful pareasthesiasPat
Pathophysiology
Neuropathic pain
- hypersensitivity of nociceptor
- spontaneous signal generated from healing neuron
- loss of modulation (descending inhibitor pathway)
- inflammation cytokines activating nociceptors
Sensation of pain
Pathophysiology
Nociceptor
- free nerve fibre
1. mechanical
2. thermal
3. chemical stimuli
Cell body located in the dorsal root ganglion
central proccess projects to the posterior horn (substantia gellatinosa, spinal gate)
Depolarization and fire action potential
First order neuron
1. a delta fibres - large, myelinated, fast (anterior tract, neospinothalamic)
2. c delta fibres - small, unmyelinated, slow (lateral tract, paleospinothalamic tract)
Second order neuron
ascending spinal tracts
- spinoreticular tract
- PONS
- arousal to pain/emotional perceptino of pain - spinomesencephalic tract
- midbrain (periaqueductal gray aera)
- modulation of pain (increase or decrease)
third order neurons
- spinothalmic tract
- third order neurons
- cortex
- emotion, cognitive, sensory processing of pain
Modulation
Facilitators
Glutamate
Glycine
substance P
prostaglandins
bradykinin
calcitonin
Modulators
Inhibitors of pain
GABA
opioids
cannabinoids
NE
serotonin
4 phases of nociception
- transduction
- transmission
- perception
- modulation
Pain threshold vs. tolerance
Life cycle
Theshold
- minimum amount of pain needed to register as stimuli
- lowers with repeated painful stimuli
- lower in infant and older adult and potentially child
Tolerance
- how much patient can tolerate
- varies individual and time
- decrease tolerance - stress, fatigue
- increase tolerance - opioids, CBT, distraction
Endogenous opioids
Morphine like neuropeptides
- endorphines
- enkephalins
- dynorphins
- endomorphins
- mu, kappa, delta receptors
- bind to neurons
- inhibit ion channels
- neuromodulation of pain
- prevent depolarization and activation of the pain signal (cannot release excitatory neurotransmitters in the posterior horne
Ecosanoids = Endocannabinoids
synthesized from phospholipids
CB1 receptors in CNS
prevent excitatory NT release in posterior horn, midbrain, thalamus
pain decreased
CB2 receptors
memory, appetite, sleep, thermoregulation, addiction
Modulation of pain
Pathways
- Descending pathway from midbrain
- synapse on interneuron in posterior horn
- turns the neuron ON
- release of inhibitory NT (GABA, opioids, NE, serotonin, cannabinoids)
- prevent afferent pain signal (excitatory pain signal)
- Cognitive expectation can turn on the descending inhibitory pain modulation pathway
SEGMENTAL pain inhibition
- Modulation of pain from periphry
- A beta fibres skin
- rubbing them sends afferent signal to the same interneuron in posterior horn
- turns on inhibition
- release of inhibitory NT
- decrease pain transmission from afferent nerve
HETEROSEGEMETNAL pain inhibition
- two noxious stimuli at the same time
- pain inhibits pain
Non pharmacological therapy pain
pathophysiology
Exercise
- release endogenous opioids
- bind to neurons, inhibit release of excitatory (painful signals)
CBT/mindfulness
- cognitive signal
- descending apthway activated
- activates inhibitory interneurons in the posterior horn
massage, accupuncture, hot/cold
- activates pain
- heterosegmental
- two pain signals, one cancels out
