Abstract
Acute (normal) pain transmission is part of a survival response to prevent tissue damage and attend to and protect damaged tissue. A cycle of afferent transmission, response to stimuli, followed by temporary hypersensitivity, then attenuation and resolution occurs. Primary afferent, spinal cord ascending and descending pathways are fixed; however the response elicited is highly dynamic and not a linear relationship with input intensity. Somatic inputs are topographically accurate, in contrast to diffuse visceral inputs. Primary afferents code differentially for stimuli (heat, acid, pressure etc) and intensity. The dorsal horn allows extensive modulation of initial inputs, either excitation or inhibition. Higher CNS areas allow extensive modulation of inputs, account for the conscious recognition of pain: the intensity, location, emotional and memory aspects. Descending pathways arising from midbrain regions can be inhibitory or excitatory.
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