Week 2-Pain & Opioids Flashcards
What is the definition of pain?
Physical, emotional, and psychological condition that does not necessarily correlate to the degree of tissue damage present.
What are components of the phenomenon known as pain?
Sensory-discriminative & Motivational-affective
Define sensory-discriminative.
component of pain depends on ascending projections of tracts (including the spinothalamic and trigeminothalamic tracts) to the cerebral cortex. Sensory processing at these higher levels results in the perception of the quality of pain (pricking, burning, aching), the location of the painful stimulus, and the intensity of the pain.
Define motivational-affective.
responses to painful stimuli include attention and arousal, somatic and autonomic reflexes, endocrine responses, and emotional changes
What effect does pain have on society?
Great cost to society in treatment and loss of production
What are nociceptors?
Pain receptors, Specialized class of primary afferents that respond to intense, noxious stimuli in skin, muscles, joints, viscera, and vasculature.
What stimuli do nociceptors respond to?
Respond to thermal, mechanical, and chemical stimuli
What information do nociceptors provide to the CNS?
location and intensity of the stimuli
Nociceptors are generally ________________
Generally inactive until stimulated by enough energy to reach the stimulus threshold
What are the four components of nociception (The experience of pain involves a series of complex neurophysiologic processes)?
transduction, transmission, modulation, and perception.
Nociception is the ________system’s response to certain harmful or potentially harmful stimuli
sensory nervous system
Define transduction.
Process by which noxious stimuli (heat, cold, mechanical distortion) are converted to nerve electrical impulses in sensory nerve endings
Define transmission.
Conduction of those impulses to the CNS (dorsal horn of the spinal cord and thalamus which has projections to cingulate, insular, somatosensory cortices)
Define modulation.
Process of altering pain transmission–CNS/PNS inhibitory & excitatory mechanisms
Define perception.
Mediated through the thalamus acting as the central relay station for incoming pain signals and the primary somatosensory complex which serves to discriminate specific sensory experiences
Does the occurrence of pain depend on all four steps of nociceptive process? What is an example of when this wouldn’t occur?
No
For example, pain from trigeminal neuralgia occurs in the absence of transduction of a chemical stimulus at a nociceptor reflecting axonal discharges initiated at the site of a compressed or demyelinated nerve. Modulation of pain impulses may not occur if specific nervous system tracts are injured. For example, phantom limb pain occurs in the absence of nociception or nociceptors (pain receptors).
Specific types of nociceptors react to ________.
different stimuli
What is the reaction of the alpha delta peripheral nerve fibers?
Fast pain (sharp pain)
Is the alpha delta peripheral nerve fibers myelinated or unmyelinated?
Myelinated
What is the fiber diameter of the alpha delta peripheral nerve fibers?
2-5 mm
What is the reaction of the C peripheral nerve fibers?
Slow pain (+cold, throbbing, burning)
Is the C peripheral nerve fibers myelinated or unmyelinated?
Unmyelinated
What is the fiber diameter of the C peripheral nerve fibers?
0.4-1.2
Cell damage results in disruption of phospholipid membrane causes the release of _______________ to became various eicosanoids which include prostaglandins
arachidonic acid that is acted upon by intracellular COX enzymes (cyclo-oxygenase)
Ascending pathways: How do nerve endings respond?
Nerve endings responding to noxious stimulus (chemical mediators) send signals (action potentials) from site of injury to the dorsal horn (1st order neuron)
Where are the noxious pain signals sent?
dorsal horn (1st order neuron)
Ascending pathways: What happens after 1st order neurons synapse with 2nd order neurons?
- Main neurotransmitter: Substance P
- Relay area of spinal cord: substantia gelatinosa part of the Rexed laminae- grey matter dense with other interneurons
Ascending pathways: What is the main neurotransmitter after the 1st and 2nd order synapse?
Substance P
Ascending pathways: What is the relay order of the spinal cord?
substantia gelatinosa
Ascending pathways: What is the cross process of 2nd order neurons?
- cross (decussate) to contralateral side to enter spinothalamic tract to ascend to brain (thalamus) Pain, temperature, itch
- Other ascending tracts, some ipsilateral
Ascending pathways: Where do 2nd order neurons connect?
2nd Order neurons connect at the thalamus (relay station in the brain) to relay with 3rd order neurons (thalamocortical)
Ascending pathways: What is the result of 2nd order neurons connect at the thalamus, in response to pain?
- Location & Discrimination of pain
- Impulse to specific area of brain related to anatomic injury
Ascending pathways: What response to pain is found in Cingulate and Insular Cortices (via the amygdala)?
- Deep, dull pain that is poorly localizes
- Emotional, affective component (fear, anxiety, depression)
What is the function of the descending pathway of pain?
Responsible for controlling/inhibiting pain
Descending pathway: What are the priority neurotransmitters involved?
Serotonergic/adrenergic (NE) neurotransmitters
Descending pathway: What are the two major anatomical pathways located?
Periaqueductal grey (PAG) & Rostral Ventromedial Medulla (RVM)/Nucleus Raphe Magnus
Descending pathway: Where is Periaqueductal grey (PAG) located?
midbrain
Descending pathway: Where is Rostral Ventromedial Medulla (RVM)/Nucleus Raphe Magnus located?
brainstem
Descending pathway: Where does the Periaqueductal grey (PAG) receive signals from?
Receives signals from autonomic cortex, thalamus, amygdala
Descending pathway: Where does the Rostral Ventromedial Medulla (RVM)/Nucleus Raphe Magnus receive signals from?
Receives signal from PAG
Descending pathway: What is the major neurotransmitter of the Periaqueductal grey (PAG)?
Norepinephrine
Descending pathway: What is the major neurotransmitter of the Rostral Ventromedial Medulla (RVM)/Nucleus Raphe Magnus?
Serotonin
Descending pathway: Where does the PAG/RVM system modulate pain?
dorsal horn
Descending pathway: What is the function of the dorsal horn in relation to the PAG/RVM system?
- Stimulate an interneuron to release endogenous opioid: enkephalins
- Prevent release of Substance P thus inhibiting nociceptive pain transmission
Descending pathway: What is stimulated by the dorsal horn?
interneuron
Descending pathway: What does the PAG/RVM system contribute to?
PAG/RVM system contributes to hyperalgesia & allodynia (stimuli that is not normally painful)
Descending pathway: What is the relationship of the PAG/RVM system to pain management?
major site of opioid based analgesia:
The direct inhibitory effects of μ receptors
& The modulating effects of κ receptors
What is the mechanism for chronic pain development?
Chronic pain occurs if the conditions associated with inflammation do not resolve, resulting in sensitization of peripheral and central pain signaling pathway and increased pain sensations to normally painful stimuli (hyperalgesia) and the perception of pain sensations in response to normally nonpainful stimuli (allodynia)
Define peripheral sensitization.
Increased responsiveness of peripheral neurons responsible for pain transmission to heat, cold, mechanical, or chemical stimulation.
What is released during peripheral sensitization?
multitude inflammatory mediators
Where do peripheral sensitization mediators work?
Mediators can work directly on nociceptive nerves or activate inflammatory cells to release chemicals
What key chemicals are involved in peripheral sensitization?
bradykinin, prostaglandin E2, histamine, cytokines thromboxane, endo-cannabinoids
What various receptors are involved in peripheral sensitization (5)?
TRPV1, purinergic, metabotropic, glutamatergic, ion channels
What is gate theory?
Larger, faster Aβ fibers override/close the gate of the pain transmission sent by smaller, slower Aδ and C fibers in the dorsal horn (mechanism for massage, acupuncture, nerve stimulators)
Where does gate theory occur?
dorsal horn
What are some types of pain?
Neuropathic and Visceral
Define neuropathic pain.
Persists after injury/healing and can be difficult to manage
What changes to the neuron result from neuropathic pain (3)?
Blocking/scarring of axon regeneration, Hyperalgesia, allodynia
What is the characterized difference between visceral and somatic pain?
While somatic pain is easily localized with distinct sensations, visceral pain is diffuse and poorly localized.
Visceral pain is associated with _____________
stronger emotional responses
How is viscera unique?
that each organ receives innervation from two nerves (pelvic and spinal or vagal and spinal)
Which fibers are effected in visceral pain?
Predominantly Aδ and C fibers
Spinal visceral nociceptors ________ neurons in dorsal root ganglion same as ______ nociceptors (get referent pain).
afferent; somatic nociceptors