Pain Pathway (2) Flashcards
What are the 2 components of pain?
Sensory (discriminative)
Motivational (affective)
What are the ascending pain pathways?
Spinothalamic and Tigemino-thalamic tracts
What part of the brain does pain transmit to?
Cerebral cortex for perception of pain
Responses to painful stimuli include:
Attention and arousal
Somatic and autonomic reflexes
Endocrine responses
Emotional changes
Why is pain described as having complex nature?
emphasizes the complex nature of pain as a physical, emotional, and psychological condition
What is nociception? What do medications target?
The experience of pain with a series of complex neurophysiologic processes
Meds target causes of pain by actions on transduction, transmission, interpretation, and modulation in both PNS and CNS.
Hyperalgesia:
Increased pain sensations to normally painful stimuli
Allodynia:
Perception of pain sensations in response to normally non-painful stimuli
Chronic pain in ___% of the population
40%
Annual cost related to pain:
$40 billion (not including surgery and lost workdays)
Most common reason for people seeking medical care:
Pain
Low back pain __% - ___% in people 45-60y/o
8-37
What is the pathway after nociception stimulation?
- Transduction
- Transmission
- Modulation
- Perception
Nerve/electrical impulses/signals start at the nerve endings:
Transduction
Travel of nerve/electrical impulses to the nerve body connecting to the dorsal horn of the spinal cord:
Transmission
Process of altering (inhibitory/excitatory) pain transmission mechanisms at the dorsal horm to the PNS and CNS:
Modulation
Thalamus acting as the central relay station from incoming pain signal and the primary somatosensory cortex serving for discrimination of specific sensory stimuli:
Perception
What is the central relay station for incoming pain signals?
Thalamus
Where is the primary discrimination area for specific sensory stimuli?
Somatosensory Cortex
Where does modulation of pain transmission occur?
Dorsal horn
Where does transduction of nerve impulses start?
Nerve endings
What meds affect transduction of pain from mechanical, chemical, and thermal stimuli into action potentials?
LA, NSAIDS (peripheral nociceptors)
What med modulates transmission of pain action potentials via A delta and C fibers?
Local Anesthetics
What meds modulate afferent signals of pain in the dorsal horn of spinal cord?
LA, opioids, ketamine, A2 agonist
What meds alter perception of pain by activating descending inhibitory pain pathway and memory?
Opioids, A2 agonists, General Anesthetics
Where does the modulation of pain impulses occur?
Dorsal horn
Where are nociceptors located?
- Skin
- Muscles
- Joints
- Viscera
- Vasculature
How does pain pathway progress from peripheral nerve?
Stimulus→ nociceptor→ resting threshold → transmission→modulation→interpretation
What type of fibers are afferent unmyelinated fibers? What type of pain is transmitted on these fibers?
C fibers: burning pain from heat and pressure from sustained pressure
What type fibers (I and II) are afferent myelinated fibers?
Type I fibers ( Aβ & Aδ fibers): heat, mechanical, chemical
Type II fibers (Aδ fibers): heat
What are the chemical mediators for pain in the periphery?
Peptides (substance P, Calcitonin, bradykinin, CGRP)
Eicosanoids
Lipids (PGs, TXA, leukotrienes, endocannabinoids)
Neutrophins
Cytokines
Chemokines
Extracellular Proteases and protons
What chemical mediator is released first in response to pain?
Bradykinin
What do chemical mediators of pain cause?
Vasodilation, Inflammation, expansion of pain
Decreased pain threshold at the original site of injury from heat and mechanical injury:
Primary hyperalgesia
What happens as a result of Primary hyperalgesia?
Decreased pain threshold
Increased response to suprathreshold stimuli
Spontaneous pain
Expansion of receptive field
Uninjured skin surrounding the injury (only mechanical stimuli):
Secondary Hyperalgesia
What happens with secondary hyperalgesia?
Sensitization of central neuronal circuits
What is the relay center for nociceptive and other sensory activity in the CNS?
Spinal dorsal horn
What is the path for the ascending pain pathway?
Goes to brainstem and forebrain→perception of pain location and intensity
What is another term for lamina I? What fibers synapse here?
Lamina marginalis
Afferent C fibers
What is another term for lamina II? What fibers synapse here?
Substantia Gelatinosa
Afferent C fibers
Where do myelinated fibers synapse? What are they innervating?
Lamina I, IV, VII and ventral horn (A fibers)
Innervating muscles and viscera
Which lamina do opioids work to inhibit pain transmission?
Lamina II
Which lamina affect NKI receptor with substance P?
Lamina III and IV
When did the gate control theory of pain come about?
1965
What does the “gate open” indicate? What fibers are involved when gate is open?
Pain is projected to supraspinal brain regions
A delta fibers (small, myelinated) and C fibers (unmyelinated)
What does “gate closed” indicate? What fibers are involved?
Pain is not felt with simultaneous inhibitor impulses (EX: rubbing bumped elbow)
A beta fibers (larger diameter and myelinated)
Which fibers deliver info about pressure and touch?
A beta fibers→large, myelinated
Where is perception of motivational-affective pain components sent?
Limbic cortex and thalamus
Area in the brain that depresses or facilitates the integration of pain info in the spinal dorsal horn:
Periaqueductal gray (PAG) / Rostral Ventromedial Medulla (RVM)
Neuromodulators of the CNS:
- Substance P
- Glutamate
- CGRP
- NMDA
- AMPA
- BDNF
- Cytokines
Tissue injury releases _______ and ________ to the nociceptor.
- Substance P
- Glutamate
What mediators do damaged cells, mast cells, and platelets release?
- Bradykinin
- Histamine
- PGs
- Serotonin
- H+ ions
- Lactic Acid
A excitatory impulse mediator:
Glutamate
Excitatory impulse modulation in the spinal cord:
- Glutamate
- Calcitonin
- Neuropeptide Y
- Aspartate
- Substance P
Inhibitory impulse modulation in the spinal cord:
- GABA
- Glycine
- Enkephalins
- Norepinephrine
- Dopamine
What are the different ascending pathways of nociceptive info?
- Spinothalamic
- Spinomedullary
- Spinobulbar
- Spinohypothalamic
Which ascending pathway is responsible for pain, temp, and itch?
Spintothalamic (lamina I, VII, VIII) all afferent fibers
Which ascending pathway involves the behavior toward pain?
Spinobulbar (laminae I, V, VII)
Which ascending pathway involves autonomic, neuroendocrine, and emotional aspects of pain?
Spinohypothalamic (Laminae I, V, VII, and X)
What part of the forebrain is involved with identifying pain location?
SI: primary somatosensory cortex
What part of the forebrain is involved with intensity of pain?
SII
Where does supraspinal modulation of nociception occur?
- Forebrain (SI and SII)
- Anterior cingulate cortex ()ACC
- Insular cortex: ACC and IC: emotional/motivational aspects
- Prefrontal Cortex
- Thalamus
- Cerebellum
Where does the descending inhibitory tract originate? Where does the signal travel through and then synpase?
Periaqueductal gray (PAG) → Travels through rostral ventromedial medulla (RVM) → dorsolateral funiculus → Synpase in dorsal horn
What neurotransmitters are involves in descending inhibitory tract?
Endorphins, Enkephalins, Serotonin
What is the MOA of descending inhibitory tract?
Hyperpolarize: uses A delta and C fibers
Decrease release of substance P→ opening of K+ channels/ inhibition of Ca++ channels
What factors affect the descending inhibition/facilitation pathways?
Other somatic stimuli: lack of sleep, stress, prior experiences, etc
Psychosocial factors: arousal, attention, and expectation
Which receptors are part of the the PAG-RVM system?
Mu, Kappa, Delta
(hyperalgesia and allodynia)
Where does the pain impulse originate if it is pertaining to the descending inhibitory tract?
PAG-RVM
How long does pain have to last to classify as chronic?
> 3-6 months→ persists beyond tissue healing
Unpleasant emotional experiences use the same pathways as ________ __________.
Chronic pain
anxiety, depression, cognitive deficits, emotional distress
Type of pain that persists after the tissue has healed:
Neuropathic pain→ allodynia and hyperalgesia
Who is at increased risk for neuropathic pain?
Cancer patients d/t chemo and radiation therapy
What is the treatment for neuropathic pain?
Treat based on symptoms (opioids, gabapentin, amitryptiline, cannabis)
Diffuse, poorly localized pain: What are causes of this?
Visceral Pain
Ischemia, Stretching of ligament attachments , spasms, distention
Complex Regional Pain Syndromes:
A variety of painful conditions following injury in a region with impairment of sensory, motor, and autonomic systems
Spontaneous pain, allodynia, hyperalgesia, edema, autonomic abnormalities, active and passive movement disorders, and trophic changes of skin & SQ tissues
How does the CV system respond to pain?
↑BP
↑HR
↑SVR
↑ myocardial irritability
↓CO
↓Myocardial ischemia
How does pulmonary system respond to pain?
↑ total body O2 consumption/CO2 production
↑ Vm and work of breathing
Splinting
Decreased movement of chest wall
Atelectasis
Intrapulmonary shunting
Impaired coughing
How does GI/GU respond to pain?
Increased sphincter tone
Decreased mobility (ileus, urinary retention)
Hyper secretion of acid (stress ulcers, aspiration)
N/V
ABD distention (decrease peristalsis)
Endocrine system response to pain:
↑ catabolic hormones
* Catecholamines
* Cortisol
* Glucagon
↓ anabolic hormones
* Insulin
* Testosterone
Effects
* Negative nitrogen balance
*Carbohydrate intolerance
*Increases renin, aldosterone, and angiotensin
What are hematologic responses to pain?
Stress related:
- Platelet Adhesiveness
- Reduced fibrinolysis
- Hyper-coagulability
How does the immune system respond to pain?
Stress related
- Leukocytosis
- Depressed reticuloendothelial system (increased infection)
What are some emotional responses to pain?
- Anxiety
- Sleep disturbance
- Depression
