Lecture 11: Pain Flashcards
What is pain?
an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage
What is nociceptive pain?
caused by noxious stimuli (heat, cold, intense mechanical force, chemical irritants)
adaptive, high-threshold pain, early warning system (protective)
“good” pain tells the brain to stop walking on a broken foot
What is pathological pain?
neural lesion
positive and negative symptoms
spontaneous pain, pain hypersensitivity
no adaptive benefit to the pain
maladaptive, low-threshold pain
What is allodynia?
pain due to a stimulus which normally does not cause pain
What is neuropathy?
disturbance in function or pathologic change in a nerve
What is central pain?
pain caused by a primary lesion or dysfunction in the CNS
What is neuropathic pain?
pain caused by a primary lesion or dysfunction in the NS
What is dysesthesia?
unpleasant abnormal sensation
What is paresthesia?
abnormal sensation, whether spontaneous or evoked
What is hyperesthesia?
increased sensitivity to stimulation
What is hypoesthesia?
decreased sensitivity to stimulation
What is the specificity theory of pain?
a specific pain system carries messages from pain receptors in the skin to a pian centre in the brain
originally formulated by Descartes in 1664
suggests a direct, invariant relationship between a psychological sensory dimension and a physical stimulus
What is the gate control theory of pain?
pain can be modulated
a “gate” within the spinal cord be opened or closed
G cell = gated cell
T cell = transmission cell
TENS machines work on the gate
What are the “large light” primary sensory neurons?
A-alpha and A-beta
discriminative touch
proprioception
non-painful things
What are the “small dark” primary sensory neurons?
A-delta and C
pain and temperature
nociceptor
C is true pain receptor
What are the properties of A-alpha and A-beta fibres?
myelinated
large diameter
proprioception, light touch
What are the properties of A-delta fibres?
lightly myelinated
medium diameter
nociception (mechanical, thermal, chemical)
What are the properties of C fibres?
unmyelinated
small diameter
innocuous temperature, itch
nociception (mechanical, thermal, chemical)
What are the central projections in the primary sensory neurons?
A-beta fibers project to deep lamina (III, IV, V)
A-delta to superficial (1, II) and deep (V)
C nociceptors to superficial
interneurons connect II to WDR (wide dynamic range)
lamina I neurons have projections (crossed) to STT
lamina II interneurons connect with WDR in Lamina V
WDR axons contribute to STT (spinothalamic tract)
What is sensitization and plasticity in pain pathways?
pain processing is very dynamic
signals may be “amplified” (hyperalgesia) or responses to previously innocuous stimuli may emerge (allodynia)
can serve a protective function
“sensitization” can occur at a variety of levels; peripherally or centrally
numerous mechanisms are involved
What is peripheral sensitization in the pian pathways?
tissue damage triggers inflammatory soup to be released
most mediators in the inflammatory soup don’t bind to a receptor, instead they modify and send secondary messages
second messengers modify ion channels by phosphorylation
ion channel may open at lower voltage or remain open longer
boost excitability/activity
reduced threshold for activation, increased output to a given stimulus
What is normal transmission compared to central sensitization?
“normal” EAA release
activation of AMPARs
NMDARs “silent” due to Mg2+ block
What does transmission look like in central sensitization?
“enhanced” EAA release, neuropeptides
recruitment of NMDARs
Ca2+ entry: phosphorylation (acute)
Ca2+ entry: gene transcription (long term)
reduced threshold, increased output (more action potentials)
What are the three dimensions of pain?
sensory-discriminative
affective-motivational
cognitive-evaluative
