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19 Cards in this Set
- Front
- Back
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What is pain? |
an unpleasant experience consisting of sensory and emotional components associated with actual or potential tissue damage |
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Different types
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Nociceptive (stimulation of peripheral nerve fibres) Neuropathic (affects somatosensory "feeling" system). Pain from normally non-painful stimuli (allodynia). Inflammation pain - tissue damage/infection - chemical mediators [psychogenic (physical pain caused by mental, emotional or behavioural factors)] |
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Give a brief outline of the pain pathway |
activation of nociceptors, afferent sensory fibres to dorsal horn of spinal cord, replay to brain via ascending spinothalamic tracts |
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What are Nociceptors? What can directly stimulate them? What can be a negative result of this? |
sensory receptors that detect noxious stimuli. They are free nerve endings of primary afferent A(delta) and C fibres. Inflammatory mediators (serotonin, prostaglandins, cytokines and H+, K+) are released from damaged tissues – can stimulate nociceptors directly. Also reduce activation threshold of nociceptors – primary sensitisation. Can lead to hyperalgesia |
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Types of nociceptive afferent neurones |
C-fibres, A(delta) fibres and A(beta) fibres |
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What are C-fibres? |
Main type Unmyelinated. Slow conduction rate (0.5-2 m/s). Polymodal - respond to thermal, mechanical and chemical stimuli. Very small diameter axons. Dull pain. |
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What are – A(delta) fibres ? |
– lightly myelinated, fast (5-30m/s), small diameter axons, sharp localised pain, responsible for initial reflex response to acute pain |
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What are A(beta) fibres ? |
carry non-noxious stimuli. Highly myelinated, large diameter – rapid conduction. Low activation threshold and respond to light touch – transmit non-noxious stimuli |
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Explain the pathway from Nociceptive Afferent Neurones to brain What are neurones involved? |
• A(delta) and C fibres synapse with secondary afferent neurones in dorsal horn of spinal cord. • Transmit info to nociceptive-specific neurones in Rexed lamina I and II – mainly short inhibitor interneurons • Primary afferent terminals release excitatory nts – glutamate and substance P (a tachykinin from capsaicin) • Interactions in dorsal horn between afferent, interneurons and descending modulatory pathways – determine activity of secondary afferent neurones. • Glycine and GABA – inhibitory interneurons |
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What are the two ascending tracts in spinal cord – pathways for nociceptive signals to brain |
• Spinothamalic tract – 20 afferent neurones decussate within a few segments of level of entry into spinal cord and ascend in contralateral spinothalamic tract to nuclei within the thalamus. Third order neurones then ascend to terminate in the somatosensory cortex. • Spinoreticular tract – fibres also decussate and ascend the contralateral cord to reach the brainstem reticular formation, before projecting to the thalamus and hypothalamus. Emotional aspect of pain |
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Draw a diagram for the ascending pain pathway |
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What affects pain processing in the brain? Experiments Common areas |
• Complex and subjective – affected by cognition, mood, genetics etc. • fMRI demonstrated that a large brain network is activated during acute pain experience – pain matrix • Commonest areas: primary and secondary somatosensory (S1 and S20, insular prefrontal cortex and thalamus. |
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What is the gene control theory of pain? |
inhibitory pain modulation at spinal cord level. By activating A(beta) fibres with tactile, non-noxious stimuli inhibitory interneurons in dorsal horn are activated – inhibitor of pain signals transmitted via C fibres Explains why when head bang, feels better when rubbed. |
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Diagram of gate control theory |
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What is another inhibitor? |
• Descending inhibitor
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Explain the Descending inhibitory pathway |
periaqueductalgrey (PAG) in midbrain and rostral ventromedial medulla (RWM) contain high concof opioid receptors and endogenous opioids – enkephalins, B-endorphin,dynorphin. Activation of opiate receptors at the interneuronal level produces hyperpolarization of the neurons, which result in the inhibition of firing and the release of substance P, a neurotransmitter involved in pain transmission, thereby blocking pain transmission. Descending pathways project to dorsal horn and inhibit paintransmittion. Nt used - noradrenaline and serotonin. |
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What is another type of pain? |
Neuropathic |
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Explain neuropathic pain? Cause, type and stimuli |
caused by damage to nerves in central/peripheral nervous system. Damage due to trauma, surgery, DM, ischaemia. Pain is more likely to be spontaneous. Pain may be experienced in response to a stimulus that does not usually cause pain (allodynia) or heightened response to stimulus that is usually painful (hyperalgesia). Unresponsive to analgesics |
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Conclusion
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• Pain transmission is a result of complex peripheral and central processes. • These processes can be modulated at different levels and pain perception is a result of the balance between facilitatory and inhibitory interactions. • Current areas of interest in pain research include investigating the effect of mood on pain processing in the brain and looking for novel drugs to block channels involved in pain transmission |
