Pain Physiology.
Presented At St Thomases Hospital for trainee Anaesthetists as part of their FRCA (Fellow of the Royal College of Anaesthetists) examination preparations.
2nd March 2007
67. C Ad Ab Myelination No Yes Yes Diameter 0.4-1.2 mcm 2-5 mcm Conduction velocity 0.5-2 m/s 12-30 m/s Normal sensation Slow pain Diffuse, dull Fast pain Sharp, localised, reflex withdrawal Pathological sensation Hyperalgesia Allodynia
68. C Ad Ab Threshold high high low Main Transmitters peptides EAA EAA Main receptors activated NK1,2 (neurokinin) NMDA AMPA mGlu AMPA Lamina 1,2,5 1,2,5 3,4 Target sc neurones NS (nociceptor specific) WDR LT WDR
87. Rexed’s laminae I,II Most nociceptors terminate in superficial layers via Ad and C III, IV Tactile afferents synapse V Some A project into deeper layers. V Nociceptive and tactile afferents converge (directly or via inter-neurones) V,VI Inter-neurones mainly regulate flow of nocicpetive info
107. Tract Information STT Spinothalamic tract Temp, Pain, Touch, Visceral Mediates and separates discriminative (fast) and affective (slow) aspects into different regions of the tract Anterior STT- simple touch Lateral STT- pain and temperature VPL, VPM, PO nuclei- conscious perception of pain SRT Spinoreticular tract To reticular formation- arousal-emotional pain. Slow pain SMT SPT
110. Direct (fast) Indirect (slow) Tract Lateral STT Lateral STT SRT Origin I, IV, V I, IV, V (+VII,VIII) Somatotopic organisation Yes No
111. Direct (fast) Indirect (slow) Body representation Contralateral Bilateral Synapse in RF No Yes Sub-cortical targets None Hypothalamus Limbic system Autonomic centres
112. Direct (fast) Indirect (slow) Thalamic nucleus VPL Intra-laminar nuclei Other midline nuclei Cortical location Parietal lobe Cingulate gyrus Role Discriminative pain (quality, intensity, location) Affective-arousal component of pain Other functions Temperature Touch
153. Term Definition Allodynia Pain due to a stimulus which does not normally provoke pain Analgesia Absence of pain in response to stimulation which would normally be painful Central Pain Pain initiated or caused by a primary lesion or dysfunction in the CNS
154. Dysaesthesia An unpleasant abnormal sensation, whether spontaneous or provoked Hyperalgesia An increased response to a stimulus which is normally painful
155. Hyperaesthesia Increased sensitivity to stimulation, excluding the special senses Hyperpathia A painful syndrome characterised by an abnormally painful reaction to a stimulus, especially a repetitive stimulus, as well as an increased threshold Hypoalgesia Diminished pain in response to a normally painful stimulus Neuralgia Pain in the distribution of a nerve or nerves Neuritis Inflammation of a nerve or nerves
156. Neuropathic Pain Pain initiated or caused by a primary lesion or dysfunction in the nervous system Neuropathy A disturbance of function or pathological change in a nerve: in one nerve, momoneuropathy; in several nerves, momoneuritis multiplex; if diffuse and bilateral, polyneuropathy Pain threshold The least experience of pain which a subject can recognise
157. Pain tolerance level The greatest level of pain which a subject is prepared to tolerate Paraesthesia An abnormal sensation, whether spontaneous or eveoked
179. RCT evidence of effect of drugs on evoked pain Drug Effect on Tramadol Mechanical allodynia TCA Mechanical allodynia Gabapentin Cold allodynia Opioids Skin hypersensitivity IV lidocaine Mechanical allodynia Topical lidocaine Mechanical and thermal hyperalgesia