Normal Pain Transmission

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.