Chapter 32 Analgesia and relief of pain
All pain receptors are free nerve endings and are called nociceptors. These are part of the process that transmits the pain to the brain (the process of nociception). Various sensory receptors found throughout the body react to a variety of stimuli, such as hot, cold, pressure and chemical, all of which can give the patient the subjective experience of pain. Different types of neuron carry the pain signal to the central nervous system (CNS):
Synapses are formed by both A and C fibres in the dorsal horns (dorsal or posterior columns) of the spinal cord. There is also regulation of the transmission between the nociceptive neurons and those in the spinothalamic tract. Descending fibres from the higher centres can inhibit transmission.
Bradykinin (Figure 32.3) is released when tissue is damaged and so is found in inflammatory processes, e.g. joint inflammation. It stimulates and sensitizes nerve endings, which leads to the stimulus that registers pain with the body. Anti-inflammatories and aspirin inhibit prostaglandin synthesis and therefore the release of mediators that create pain (see Chapter 30 ‘Inflammation and the immune system’, p. 228).
Analgesics
Sites of Action
Terminology

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