Pain Flashcards
Pain
A perception, not a stimulus, has no definitive physical dimensions
Most modifiable system of the body
Sensory experience evoked by stimuli that injure or threaten to injure tissue
Reticular formation
Makes up central core of brainstem, characterized by aggregations of cells of different types and sizes, interspersed with wealth of nerve fibers traveling in many directions and excludes organized groups of cells
Allodynia
Normally non-nociceptive stimulus is painful
Perception of event
Consciousness via cerebral cortex -> loss of reflex doesn’t correlate to a loss of pain perception
Conditions producing absences of nociceptive reflex
Lost afferent supply to region where noxious stimulus is applied
Damage to spinal cord segment mediating reflex
Lost efferent supply to limb flexors
Trauma, peripheral neuropathies
Myoneural transmission blockage
Hyperreflexic nociceptive reflexes if spinal cord is damaged cranial to limb tested
Total loss of pain response to deep pain stimuli
Serious, irreversible damage to spinal cord
Reflex arcs
Involve multisynaptic excitation of ipsilateral flexor LMNs and inhibition of ipsilateral extensor LMNs
If standing, elicitation of nociceptive reflex in one limb results in contralateral extension reflex (doesn’t happen in recumbency)
Medial spinothalamic pathway
Located ventromedially
Ipsilateral and bilateral components, motivational afferent pathway
Supraspinal destination: medullary reticular formation and midline and intralaminar nuclei
Spinoreticular pathway
Located ventromedially, just lateral to propriospinal pathway
Supraspinal destination: medullary and pontine reticular formations, terminate in nuclei of medullary RF or project rostrally to medial and intralaminar thalamic nuuclei
Medial system
Conducts impulses arising from stimuli that have produced actual damage to animal
Motivational affective dimensions of pain sensation
Terminate almost exclusively in intralaminar and midline nuclei in reticular formation
Cerebral cortex involvement in nociception
No specific area uniquely responsible for perception of pain
Nociceptive pathways project to midline, intralaminar, and ventral thalamic nuclei
Diencephalon involvement in nociception
Serves as relay for most activity entering cerebral cortex from pathways originating in brainstem and spinal cord, with exception of olfactory system
Mesencephalon involvement in nociception
Electrical microstimulation produces profound state of analgesia
Medullary and pontine reticular formation
nociceptive input
Acute pain
Brief, usually elicits avoidance behavior
Nociceptors
Receptors involved in pain, respond to noxious stimuli
Free nerve endings in skin and viscera
Terminal ending of peripheral process of a nociceptive fiber that conducts in A-delta and C fiber conduction velocity range
Afferents terminate in superficial layers of dorsal horn
Noxious stimuli
Strong mechanical pressure, heat, excessive cold, chemical substances, high electrical stimulation
Sensory-discriminative dimension
Addresses questions of where, what, how rapidly
Motivation-affective dimension
Addresses how to avoid stimulus and how sever is the injury
Fast superficial pain
First pain, sharp, pricking
Signaled by myelinated A-delta fibers
Slow superficial pain
Second pain, aching, burning, deep pain
Signaled by unmyelinated C nociceptor fibers
Chronic pain
Lasts longer (months-years) and usually associated with suppression of activity and depression Can alter other pathways, sensitivity, hormonal balance, etc.
Spinocervicothalamic pathway
Ascends in dorsal part of lateral funiculus
Responds to noxious thermal and mechanical stimulation and fibers responding to low-threshold mechanical stimulation
Supraspinal destination: central and caudal part of VPL of thalamus
Dorsal column-postsynaptic pathway
Located just medial to dorsal horn
Bilateral pathway, carries info from visceral structures
Supraspinal destination: VCL of thalamus
Propriospinal pathway
Located just lateral to ventral horn
Supraspinal destination: medullary and pontine reticular formation
Nociceptive reflex behavior
Withdrawal reflex
Involves flexion of limb
Involve at least 3 spinal cord reflexes and many simultaneously acting reflex mechanisms
Only dependent integrity of reflex arc
Pain perception
Voluntary act by which an animal demonstrates that it has perceived a noxious stimulus as painful (cerebral cortex)
Requires integrity of afferent fibers and ascending and descending pathways
Criteria used to determine whether a given stimulus gives rise to pain or whether animal is showing non-perception linked reflexes
Stimulus, in normal animal, must be perceived as pain
Stimulus must threaten or actually destroy tissue
Animal must show aversive response to stimulus
Injury to CNS to drugs used, cerebral cortex must be in a state in which perception can occur (tests include menace visual placing, tactile placing, conscious proprioception, EEG)
Nociceptor threshold
Minimum noxious stimuli required to generate nerve impulses in a nociceptor
Pain-detection threshold
Minimum noxious stimulus applied that gives rise to the perception of pain
Emphasizes discrimination of nociceptive quality
Varies with stress and anxiety
Pain-tolerance threshold
Maximum noxious stimulus tolerated under experimental conditions
Expression of willingness to receive more intense stimulation
Lateral system
Conducts impulses that lead to perceptions about precise location, qualitative nature and areal extent of stimulus
Terminate predominantly in lateral group of nuclei (VPM, VPL, VL, POM)
Lateral spinothalamic pathway
Located ventrolaterally
Ipsilateral and bilateral components, sensory discriminative pathway
Supraspinal destination: VPL, VL, and intralaminar nuclei of thalamus
Pain-sensitivity range
Difference between the pain-detection threshold and the pain-tolerance threshold
