Pain physiology / Flashcards
What are the somatosensory tracts and what information they carry?
CONSCIOUS
DCML: fine touch, vibration and proprioception
Anterior spinothalamic: crude touch and pressure
Lateral spinothalamic: pain and tmeprature
UNCONSCIOUS
4 spinocerebellar tracts: proprioception
What are the neurons in the ascending somatosensory pathways?
Sensory neurons - 1st order
Spinal cord/brainstem - 2nd order
Thalamus - 3rd order
What are the different categories of somatosensory receptors?
Mechanoreceptors
Nociceptors
Thermoreceptors
What are the different types of somatosensory mechanoreceptors and what do they detect?
Meissner corpuscles - light touch
Merkel discs - pressure
Pacinian corpuscles - vibration
Muscle spindles - limb position
What are the different types of nociceptors and what do they detect?
A-delta mechanical (encapsulated) - pin prick
C-polymodal (free nerve endings) - tissue damage
What are thermoreceptors in the form of?
Free nerve endings detect cold or warmth
What are the classes of somatosensory nerve fibres and what sensations do they detect? Are they myelinated?
Alpha: proprioception (myelinated
Beta: pressure and vibration (myelinated)
Delta: fast pain, cold (myelinated)
C: slow pain, warmth (unmyelinated)
Nociception vs pain
Nociception is the physiological response to noxious stimuli
Pain is an experience
Pain is commonly a response to nociception
Pain is possible without nociception
What processes are involved in pain physiology?
Transduction
Transmission
Perception
Modulation
What is pain transduction?
Transforms noxious stimuli into electrical stimuli
Noxious stimuli causes cell damage with the release of sensitising chemicals e.g. prostaglandins, bradykinins, serotonin, substance P, histamine
Or stimulate mechanically gated Na+ and Ca2+ channels
Heat sensitive ion channels
Mast cells
These stimuli activate nociceptors and lead to generation of action potential
Can be due to temperature extremes, trauma, hypoxia, chemicals
What is pain transmission?
Conduction of electrical stimulus through the NS
1st order neurone: A-beta/A-delta & C. Synapse at dorsal horn
2nd order neurone: decussate, ascend in lateral spinothalamic tract
3rd order neurone: through thalamus to sensory cortex
What is pain perception?
Subjective sensation of pain
Influenced by:
Thalamus/sensory cortex: localisation
Limbic cortex: emotional response
Reticular formation: alertness
Autonomic interconnections
What is pain modulation?
Process of alterations in pain signals along the transmission pathway of pain
Gate control theory: pain signals can be disrupted in the substantia gelatinosa which acts as the gate. When sensory impulses are greater than the pain signals, this can close the gate and restrict pain signals reaching the brain
Descending inhibitory pathway: suppresses pain to allow organism to function enough to respond to pain
Neurotransmission: Excitatory NT: glutamate and excitatory NP: substance P. Inhibitory NT: GABA, norepinephrine, 5HT, inhibitory neuropeptide: enkephalins
