Somatosensation and Pain Flashcards
What does the limbic system play a key role in?
regulating emotions, memory and behaviour
What does the limbic system include?
- amygdala
- hippocampus
- hypothalamus
What is the role of the amygdala?
- processes emotions like fear, anger and pleasure
- helps recognise emotional cues
- triggers fight or flight response
What is the role of the hippocampus?
declarative memory i.e. crucial for forming and retrieving memories linked to emotions to contextualise emotional experiences based on past events
What is the role of the hypothalamus?
controls autonomic functions like heart rate, blood pressure, and hormone release, which are linked to emotional states
How does pain serve as a critical protective mechanism?
it alerts the body to potential or actual harm
What are the 3 main components of pain?
- sensory-discriminative aspect
- affective-motivational aspect
- cognitive-evaluative aspect
What does the sensory-discriminative aspect of pain involve?
the physical sensation of pain, including its intensity, location, quality and duration
What is the mechanism of the sensory-discriminative aspect of pain?
pain signals are initiated by nociceptors and transmitted through peripheral nerves to the spinal cord and then to the brain, where they are processed primarily in the somatosensory cortex, allowing the individual to localise and describe the pain
What does the affective-motivational aspect of pain refer to?
the unpleasant emotional and psychological responses associated with pain, such as fear, anxiety, and the urge to escape the painful stimulus regulated by the limbic system
What does the cognitive-evaluative aspect of pain involve?
the interpretation and meaning assigned to the pain experience, including beliefs, attitudes, and expectations about pain, as well as coping strategies
What is nociceptive pain?
pain that results from actual or potential tissue damage, typically protective in nature, often described as sharp, aching, or throbbing
Give an example of nociceptive pain
pain from a cut, burn, or broken bone
What is neuropathic pain?
(often chronic) pain caused by damage to or dysfunction of the nervous system itself, described as burning, shooting, or electric shock-like
Give an example of neuropathic pain
pain from diabetic neuropathy, shingles or nerve compression
What is inflammatory pain?
pain associated with inflammation, which occurs when the body’s immune response triggers the release of chemicals that sensitise nociceptors
Give an example of inflammatory pain
pain from rheumatoid arthritis
What is chronic pain?
pain that persists for longer than 3-6 months, often resulting from ongoing tissue damage, nervous system dysfunction, or sensitisation
Give an example of chronic pain
chronic back pain, fibromyalgia, migraine headaches
What is pain intensity?
the sensory dimension of the pain experience, which often translates into the quantity of the pain experienced
What is pain unpleasantness?
the emotional dimension of the pain experienced, or the extent to which the pain is considered uncomfortable or bothering
What happened to neural activity in the ACC when pain unpleasantness was decreased via hypnosis?
it also decreased
What happens when pain signals reach the ACC?
they trigger emotional and behavioural responses aimed at avoiding or escaping the painful stimulus
What does activity in the ACC correlate to?
the subjective feeling of how unpleasant the pain is, rather than just the intensity of the pain stimulus
What is allodynia?
pain to a normally non-painful stimulus
What are possible mechanisms of touch allodynia?
- peripheral sensitisation
- central sensitisation
- disinhibition
- aberrant sprouting
- altered brain processing
- involvement of glial cells
When does peripheral sensitisation occur?
when PNS nociceptors become more sensitive and responsive to stimuli
What is the mechanism of peripheral sensitisation?
after tissue injury or inflammation, nociceptors can lower their threshold for activation, meaning that even light touch can activate them and send pain signals to the brain (inflammatory mediators can also contribute to this)
What is the result of peripheral sensitisation?
increased sensitivity of primary afferent neurons (especially Aδ and C-fibres)
What is central sensitisation?
increased responsiveness of CNS neurons, particularly in the dorsal horn of the spinal cord, to normal or subthreshold sensory input
What are the 3 mechanisms of central sensitisation?
- increased synaptic efficiency (repeated stimulation of nociceptors → increased neurotransmitter release and activation of NMDARs in dorsal horn neurons → LTP)
- loss of inhibitory control (inhibitory interneurons become less effective through loss of GABA or glycinergic inhibition)
- spinal cord rewiring (Aβ fibres synapse on neurons that normally transmit pain signals)
What is the mechanism of disinhibition?
destruction of inhibitory interneurons, such as those in lamina II of the dorsal horn, leads to a loss of inhibition on pain-processing neurons
Give an example of disinhibition
the loss of dynorphin-expressing neurons, which inhibit pain pathways, can result in increased excitability of pain-transmitting neurons → touch allodynia
What is aberrant sprouting?
abnormal growth of CNS nerve fibres e.g. after injury, Aβ fibres may sprout and form new synaptic connections with neurons in the dorsal horn that usually receive input from nociceptive fibres
How can altered brain processing cause touch allodynia?
brain regions e.g. somatosensory cortex and ACC may become hyperactive or reorganised which amplifies the perception of touch leading to the sensation of pain even in response to light touch
How can glial cells cause touch allodynia?
after injury or inflammation, glial cells can become activated and release pro-inflammatory cytokines and chemokines that enhance the excitability of pain-processing neurons and enhance the central sensitisation
What is LTP?
a form of synaptic plasticity that can make neurons more responsive to incoming signals
Give examples of touch allodynia
- sprained ankle
- sunburn
- neuropathy
