Anatomy of physiology of pain Flashcards
3 types of pain
Nociceptive
Prolonged/ inflammatory
Neuropathic
Define nociceptive pain
Pain elicited by brief noxious stimulus
What is function of noxious pain
Prevent further damage
What is the result in a mutation of Nav1.7 channel
Presents with abnormal pain sensations
What is CIPA
Congenital insensitivity to pain with anhydrosis
What mutation causes CIPA
trkA
Receptor for nerve growth factor
What does trkA mutation lead to
Decreased pain sensitivity
Anhydrosis (inability to sweat)
Is prolonged/ inflammatory pain central or peripheral
Peripheral
What is prolonged/ inflammatory pain
Hypersensitivity from inflammation around an area of the body that has been injured
What is the biological function of inflammatory pain
Prevent further damage and assist tissue repair
Is chronic pain central or peripheral sensitisation
Central
Define chronic pain
Pain that has been present for 3 months that results from disease/ damage to PNS/CNS
What is neuropathic pain
Pain persists in the absence of initial injury
Several PNS and CNS abnormalities
What nerves sense pain from internal organs
General visceral afferents
What does pain from general visceral affarents respond to
Distention
Not sensitive to cutting or burning
Name the 4 stages of pain
Transduction
Transmission
Perception
Modulation
Describe phase 1 of pain
Transduction–> at the receptor
Noxious stimuli translated into electrical activity at sensory nerve endings
Describe phase 2 of pain
Transmission–> nerve fibres
Propagation of impulses along pain pathway
Describe phase 3 of pain
Perception–> areas of brain
Descrimination/ affect/ motivation
Describe phase 4 of pain
Modulation
Stages 1-3 are modified
What are nociceptors
Non-specialised receptors that use free nerve endings
Often polymodal
Define polymodal
Respond to more than one type of stimulus
Name 3 types of nociceptors
Cutaneous
Muscular
Visceral
Function of cutaneous nociceptors
Aid conversion of a noxious stimuli into an electrical impulse
What pain does TRPV1 receptor detect
heat and acid
What pain does ASIC receptor detect
Acid
What pain does TRPM8 receptor detect
Cold/ menthol
Define transmission
Travel of the receptor impulses along different pain pathways to different parts of the brain
Function of first order neurones
Carry sensory impulse from sensory receptor to CNS
What kind of pain is associated with a-delta fibres
Fast, prick pain
Function of a-delta fibres
Localising source of stimulus
What kind of pain is associated with c fibres
Slow burning pain
Where do the impulses travelling via peptide poor C fibres travel to
Dorsal horn
Where do impulses travelling via peptidergic C fibres tro travel
Dermis
Once at the dermis what do peptidergic C fibres release?
Substance P for vasodilation and mast cell histamine release
Cardinal signs of inflammation
Heat
Red
Pain
Swelling
What do first order neurones synapse with
Second order neurones
What do c fibres innervate
Lamina 1
What do a delta fibres inneravte
Project neurones at laminae 1 and 5
As well as a-delta fibres, what else does lamina 5 receive input from
A-beta
C fibres
Where does the anterior/ neo spinothalamic tract go to
Primary and secondary somatosensory cortex
Where does lateral/ paleo spinothalamic tract go
Anterior cingulate anad rostral insular cortex
Which aspects of pain does the anterior spinothalamic tract detect
Where/ how
What fibres does neo spinothalamic tract use
Fast a-delta fibres
Where does the spinothalamic tract project to
VPL and VPM of thalamus
Projects to primary and secondary cortex
What does the lateral spinothalamic tract detect
Affective- motivation
Quality of pain
What fibres does lateral spinothalamic tract use
C fibres
A-delta fibres
What does the lateral spinothalamic tract project to
Mediodorsal nucleus
Posterior thalamus- posterior nucleus and ventral mediate nucleu
Where does the MDvc project to
Anterior cingulate cortex
Where do Pom and Vmpo project to, and what information does this give
Insula
Quality of pain
What does the primary somatosensory cortex perceive about pain
Pain localisation
What does secondary somatosensory cortex perceive about pain
Pain intensity
What does insula perceive
Pain intensity
What does anterior cingulate cortex perceive
Emotion and attention
What does prefrontal cortex perceive
Emotion and memory
What is the gate control theory of modulation
Projection neurone of lamina 1
What is counter stimulation analgesia
Convergence
2 difference sensory inputs fuse into 1 when trave
Stimulation of which fibres are involved in counter stimulation analgesia
A-beta fibres that stimulaate lamina 2
What does TENS stand
Transcutaneous electrical nerve stimulators
How do TENS machine work
Stimulate a-beta fibres
Stimulate area around painful region through low intensity and high frequency stimuli
Aim to stimulate inhibitory lamina 2 interneurones
What is meant by supraspinal (descending) analgesia
Type of modulation whereby descending systems modulate the transmission of ascending pain signals
Which is the main region of the brain involved in supraspinal descending analgesia
Periaqueductal grey in main region
Deep brain stimulation of which area is used to decrease pain
Periaqueductal grey
Name 3 areas of the brain that the periaqueductal grey stimulates
Locus coeruleus
Nucleus raphe magnus
Reticular formation
What does nucleus raphe magnus transmit
Serotonin and encephalin
What is meant by arousal analgesia
Sympathetic system stimulation via reticular formation
What does arousal analgesia cause
Noradrenaline release
Activation of inhibitory lamina 2
What does phospholipase A2 releases from cell membranes
Arachidonic acid
What drugs can target arachidonic acid
Steroids
What molecules use arachidonic acid as substrate for prostaglandin synthesis
COX-1 and COX-2
Is COX-2 always present or just in inflammation
Inflammation
What is peripheral sensitisation
Increased sensivity to pain (heat induced pain means primary thermal hyperalgesia, pressure pain- primary mechanical hyperalgesia)
What is central sensitisation
Increased mechanical sensitisation extending outside the region of flare
Thermal responses normal
Why does flare occur
Release of peptides by C fibres and other local inflammatory mediators
What is dysfunctional pain
No known lesion or inflammation
How do COX-1 and COX-2 enzymes used arachnoid acid?
For prostagalndin synthesis
How do prostaglandins sensitise C fibres
Increasing number of other receptors and by increasing number of open sodium channels
What do nociceptor affarents release during central sensitisation, and what is the result of this
Glutamate and peptides
Results in increased sensitivity of dorsal horn nociceptive second order neurones to inputs
How is acupuncture thought to work?
- Activates A delta fibres
- Thus stimulating diffuse noxious inhibitory control (DNIC) of pain
- Pain can inhibit pain
