Exam 2 - Pain pathways Flashcards
What are the two components that are involved in the complex phenomenon of pain?
- Sensory - discriminative
- Motivational-affective
What is the sensory-discriminitive portion of pain?
- The perception of pain by the brain; ascending pathway
- spinothalamic/trigemino-thalamic tracts → somatosensory cortex
What is the motivational-affective portion of pain?
- The responses to painful stimuli
- Attention/arousal
- Somatic/autonomic reflexes
- Endocrine response
- Emotional response
Where does perception of motivational-affective pain occur?
Limbic cortex (emotional center) and thalamus
Term for increased pain sensations to normally painful stimuli
Hyperalgesia
Term for perception of pain sensations in response to normally non-painful stimuli
Allodynia
List the steps in the pain perception pathway
- Transduction - of pain via peripheral nociceptors
- Transmission - of pain via nerves
- Modulation - (inhibition/exitation) of pain at the dorsal root ganglion and dorsal horn
- Perception - of pain via ascending spinothalamic tract at the somatosensory cortex
This brain strutctire acts at the central relay station for incoming pain signals
Thalamus
Local anesthetics and NSAIDS alter what part of the pain pathway?
LA: transduction, transmission, and modulation
NSAIDs: transduction
Opioids, ⍺2-agoinsts, general anesthetics, and ketamine alter what parts of the pain pathway?
Opioids and ⍺2-agoinsts: Modulation and perception
Ketamine: modulation
General anesthetics: Perception
Unmyelinated C-fibers transmit what signals?
burning and pressure
Myelinated A-fibers type I and II transmit what signals?
Type I (Aβ and A𝜹): heat, mechanical, chemical
Type II (A𝜹): heat
What 4 peptides act as chemical mediators?
Substance P, calcitonin, bradykinin, CGRP
What is the first chemical mediator released?
Bradykinin
What are the lipid chemical mediators released in response to pain?
Prostaglandins, thromboxanes, leukotrienes, endocannabinoids
PELT
What are the other chemical mediators released during pain that are not lipids or peptides?
- Eicosanoids
- Neutorphins
- Cytokines
- Chemokines
- Proteases and protons
List the types of receptors and channels involved in the dorsal root ganglion and peripheral terminals?
- Purinergic
- Metabotropic
- Glutamatergic
- Tachykinin
- TRPV I
- Neurotrophic
- Ion channels
The increased responsiveness of peripheral neurons responsible for pain transmission to heat, cold, mechanical or chemical stimulation is called ____?
Sensitization
Describe primary hyperalgesia?
- Occurs at the original site of injury from heat/mechanical injury
- Causes decreased pain threshold, increased response, spontaneous pain, and expansion of the receptive field
What population has a decreasd pain threshold and exaggerated pain responses?
Neonates
Pain perception at 23 weeks
Describe secondary hyperalgesia?
Characterized by enhanced pain by mechanical stimuli in the uninjured skin
These laminae synapse with afferent C fibers?
Which one does opioids work on?
Lamina I (lamina marginalis)
Lamina II (substantia gelatinosa) - opioids work here
These laminae synapse with A-fibers from muscles and viscera?
Laminae I, IV, VIII and the ventral horn
What laminae contain the NKI receptor with substance P?
What do we do that affects these laminae?
- Laminae III and IV
- Spinal anesthesia
Briefly describe the gate control theory of pain?
There is a neurologic “gate” in the doral horn that can be opened or closed.
Opened = pain projected to supraspinal regions
Closed = pain transmission to the brain is inhibited by simultaneous inhibitory impulses
What fiber type can cause the pain gate to close?
How?
Aβ fibers (pressure/touch) - they are very large and myelinated; overriding the signals from slower nerve impulses (A𝜹 and C)
An example would be rubbing your elbow after hitting it on something- the sharp, intense pain is overridden by the pressure sensations
What two areas in the brainstem depress or integrate pain in the spinal dorsal horn?
- Periaqueductal gray
- Rostral ventral medulla
What are the 5 excitatory Neuromodulators in the CNS?
- Glutamate
- Calcitonin
- Neuropeptide Y
- Aspartate
- Substance P
GAS CaN
What are the 5 inhibitory Neuromodulators in the CNS?
- GABA
- Glycine
- Enkephalins
- Norepinephrine
- Dopamine
In the CNS, what are the 4 Ascending pathways of nociceptive information?
- Spinothalamic
- Spinomedullary
- Spinobulbar
- Spinohypothalamic
What type of impulses and laminae are associated with the Spinothalamic tract?
- Pain, temperature, and itch
- Laminae I, VII, & VIII: All afferent fibers
What type of impulses and laminae are associated with the Spinobulbar tract?
- Behavior component toward pain
- Laminae I, V, & VII
Bulbar = Behavior
These laminae cross over with the spinohypothalamic tract
What type of impulses and laminae are associated with the Spinohypothalamic tract?
- Autonomic, neuroendocrine, and emotional aspects of pain
- Laminae I, V, VII, & X
What are the 6 supra-spinal areas that are involved in modulations of nociception?
- Forebrain S I & S II (somatosensory)
- Anterior cingulate cortex (ACC)
- Insular cortex (IC)
- Prefrontal cortex
- Thalamus
- Cerebellum
This area of the brain percieves the location and intensity of pain transmissions?
Forebrain SI and SII
- This area is synonomous with the somatosensory cortex
These 2 areas on the brain are involved in the emotional and motivational aspects of pain?
- Anterior cingulate cortex (ACC)
- Insular cortex (IC)
What is the pathway for modulation of pain in the descending inhibitory tracts?
How does this inhibit pain signals?
Originates at the periaqueductal gray (PAG)
→ Descends through the rostral ventromedial medulla (RVM)
→Dorsolateral funiculus
→Synapse in the dorsal horn
Hyperpolarizes A-delta and C fibers via decreased release of substance P, opening of K+ channels/inhibition of Ca++ channels
What are the neurotransmitters used in the descending inhibitory tract?
- Endorphins
- Enkephalins
- Serotonin
The PAG-RVM system contains what 3 opioid receptors and contributes to what 2 physiological pain sensations?
- µ, κ, δ opioid receptors
- hyperalgesia & Allodynia
Why is chronic pain linked to unpleasant emotionl experiences (anxiety, depression, etc.)?
Because chronic pain has the same pathway
From A&P: the chronic pain signals stop around the limbic area of the thalamus leading to the emotional involvement.
What defines chronic pain?
> 3-6 months after injury, continuing even after tissue healing
This type of pain persists after tissue healing, characterized by reduced sensory and nociceptive thresholds (Allodynia and Hyperalgesia)?
Neuropathic Pain
Who is a increased risk for neuropathic pain?
Treatments?
- Cancer patients from chemo and radiation
- Treat the symptoms: opioids, gabapentin, amitryptiline, cannabis
Pain that is diffuse and poorly localized - referred to somatic sites like muscle and skin ?
Visceral Pain
Causes of visceral pain include:
ischemia, stretching of ligamentous attachments, spasms, and distention
The name given for a variety of painful conditions following injury in a region with impairment of sensory, motor, and autonomic systems?
Complex Regional Pain Syndromes
The CV response to pain includes:
- Hypertension
- Tachycardia
- Myocardial irritability
- ↑ SVR
If the LV if already dysfunctional, CO and myocardial ischemia will be worsened
Pain causes these pulmonary responses:
- ↑ O2 consumption and CO2 production
- ↑ WOB
- ↓ Chest wall movement and coughing → atelectasis, shunting, and pneumonia
The GI/GU response to pain includes:
- ↑ sphincter tone, ↓motility - ileus and retention
- ↑gastic acid production - stress ulcers, aspiration
- N/V
- Abdominal distention
Remeber, this is why traumas are considered full stomachs… they have greatly reduced GI functions
Pain causes an increase and decrease in what hormones?
What effects does this cause?
- ↑catabolic hormones: catecholamines, cortisol, glucagon
- ↓anabolic hormones: insulin, testosterone
Effects: negative nitrogen balance, carbohydrate intolerance, and increases in renin, aldosterone, and angiotensin
The increased stress response from pain leads to:
____ adhesiveness
____ fibrinolysis
____coagulability
Platelet adhesiveness
Reduced fibrinolysis
Hypercoagulability
Emotional responses that pain causes can lead to:
- Anxiety
- Sleep disturbance
- Depression
Immune responses to pain are:
- Leukocytosis (stress related)
- Depressed reticuloendothelial system → increased infection
