Pain Flashcards
What is nociceptive pain ?
Caused by activation of specialist nerve fibres (pain fibres or nociceptors)
Stimulated by noxious or tissue damaging stimuli
What are nociceptive receptors ?
What are the main neurotransmitters ?
What are they activated by ?
What do they lead to the release of ?
Examples ?
Receptors for pain.
Main neurotransmitters - glutamate and substance P.
Activated by thermal, mechanical, chemical noxious stimuli.
Leads to release of prostaglandins, kinins and potassium ions.
Spasms, ischaemia, contractions, distensions.
What are the types of nociceptive pain ?
Inflammatory, visceral (organs), somatic (soft tissue and bone)
What is neuropathic pain ?
What are the types ?
Long term damage to nerve fibres.
Injured nerves but normal tissues, damage to peripheral nerves, spinal, brain
Diabetes, MS, cancer, viral infections, strokes
What are the 4 parts to nociceptive pain ?
Nociception - convert noxious stimuli into nerve impulses
Transmission - nerve impulses move along pathway to brain
Perception - conscious pain
Modulation - Increase or decrease in perception of pain through gate control theory
Describe the process of nociception
End of nociceptor (neurone) detects stimuli
Axon of nociceptor travels within spinal nerve
Cell body is in the dorsal root ganglion
Nociceptor ends in dorsal horn where is connects to other sensory neurones
Pain is experienced by a sharp pain followed by a dull, aching sensation. Why is this ?
What are the types of nociceptors ?
A - Delta fibre is bigger, wider, myelinated - pressure
C - fibre - thin, smaller, non myelinated - inflammatory chemicals
Describe the process of transmission
Glutamate and substance P released from dorsal horn to stimulate rely neurones into spinal cord.
Rely neurones use white matter tract to pass signal to brain
Synapse in dorsal horn is the pain gate
Thalamus receives most of pain signal
Medulla receives some - stimulates SNS fight / flight
Describe the process of perception
Thalamus sends signal to higher brain centres to activate them, resulting in perception of pain.
Describe the process of modulation
Perception of pain influenced by factors which can modulate pain.
Describe counter stimulation
A - beta fibres respond to touch and meet at same place in dorsal horn as nociceptors
So messages from A beta fibres reduce ability of C fibres to stimulate relay neurones.
What is descending modulation ?
According to GCT -
Psychological factors activate nerve pathways that meet in dorsal horn and release endorphins, serotonin, noradrenaline which block synaptic transmission between C fibres and relay neurones, reducing pain.
What do endogenous opiods do ?
Block descending signals = reduce inhibit pain signal from brain to PNS.
Explain axonal action potentials
Sensation - depolarisation of neurone - action potentials travel to spine/brain and back. More pain - more action potentials. Higher Na+ in nociceptive receptors.
Explain neural plasticity
Reorganisation of structures, functions, connections.
Functional plasticity - brain moves functions elsewhere
Structural - brain changes physical structure.
