© UWCM/SONMS/Pain/MJohn Pathways © UWCM/SONMS/Pain/MJohn
Receptors trigger pain perception and the pain response Examples: Mechanoreceptors thermoreceptors. photoreceptors & chemoreceptors © UWCM/SONMS/Pain/MJohn
Structure of a Sensory Neurone © UWCM/SONMS/Pain/MJohn
Pain/Sensory receptors in the Hand © UWCM/SONMS/Pain/MJohn
© UWCM/SONMS/Pain/MJohn
© UWCM/SONMS/Pain/MJohn Saltatory Conduction © UWCM/SONMS/Pain/MJohn
© UWCM/SONMS/Pain/MJohn
Perception of Painful Stimuli Remember that Nociception is the response to noxious (painful) stimuli. It comes from nerve endings that respond to high intensity mechanical, thermal and chemical stimuli © UWCM/SONMS/Pain/MJohn
Pain receptors are widespread Skin, Periosteum, Joint surfaces, Arterial walls, Subcutaneous tissue Muscle, Fascia and viscera. Most deep tissues have few pain receptors (Bonica, 1990). © UWCM/SONMS/Pain/MJohn
© UWCM/SONMS/Pain/MJohn SOURCE of PAIN © UWCM/SONMS/Pain/MJohn
© UWCM/SONMS/Pain/MJohn Cutaneous fibres. myelinated, type A ‘delta' fibres or unmyelinated, type C fibres Myelinated A delta fibres conduct acute prickling type pain whereas Unmyelinated C fibres transmit the slower burning dull, diffuse, persistent unbearable pain sensations © UWCM/SONMS/Pain/MJohn
Myelinated and Unmyelinated Fibres © UWCM/SONMS/Pain/MJohn
© UWCM/SONMS/Pain/MJohn Clinical Links Ischaemia Pain from ischaemic toes is transferred via free nerve endings to the spinal cord and on to the brain even without other stimuli Distension of organs like the gut Free nerve endings that respond to such stimuli that can cause tissue damage. © UWCM/SONMS/Pain/MJohn
Tissue damage & Pain-producing substances Activating Receptors H+ and K+ - released from damaged tissue ATP - released from damaged tissue Bradykinin - released from plasma and very potent Histamine - released from mast cells Serotonin(5HT)- released from platelets around damaged tissue © UWCM/SONMS/Pain/MJohn
Sensitising Receptors Prostaglandin - released from damaged cells Substance P -released from affected nerve terminals Leukotrienes - released from Mast cell Eosinophils & Macrophages © UWCM/SONMS/Pain/MJohn
© UWCM/SONMS/Pain/MJohn Inflammation & Pain © UWCM/SONMS/Pain/MJohn
© UWCM/SONMS/Pain/MJohn Dorsal Horn Afferent Sensation reaches the Dorsal Horn It reaches s set of Lamina with the substantia gelatinosa © UWCM/SONMS/Pain/MJohn
Acute Pain Perception &Transmission Histologically, the grey matter of the spinal cord is divided into ten 'laminae'. The dorsal part is divided into five laminae (I to V), components of which deal with most incoming pain fibres. © UWCM/SONMS/Pain/MJohn
Pain Pathway to the brain © UWCM/SONMS/Pain/MJohn
© UWCM/SONMS/Pain/MJohn Spinothalamic Tract © UWCM/SONMS/Pain/MJohn
© UWCM/SONMS/Pain/MJohn Gating mechanisms 1 Tiny unmyelinated 'C' fibres carriers of the long-lasting burning pain e.g. surgical wounds. Thin myelinated 'A delta' fibres, more accurate localisation of pain, terminating in laminae I and V. Chunky 'A beta' fibres carry information on vibration + position © UWCM/SONMS/Pain/MJohn
© UWCM/SONMS/Pain/MJohn Gating Mechanism 2 Stimuli entering via the C fibres can be suppressed by concurrent stimulation of A delta fibres (high amplitude low frequency stimulation, e.g. acupuncture) or A beta fibres impulses. E.g. TENS (transcutaneous electrical nerve stimulation) and rubbing the skin, © UWCM/SONMS/Pain/MJohn
© UWCM/SONMS/Pain/MJohn Pain Modulation Peripheral tissues - At the gate Central CNS PNS © UWCM/SONMS/Pain/MJohn