Mmj

Afferent fiber

Excitatory 'short circuit (ephapse)

Smooth muscle

Alteration of microcirculation and capillary filtration

Afferent fiber

Excitatory 'short circuit (ephapse)

Smooth muscle

Alteration of microcirculation and capillary filtration

Efferent sympathetic fiber

FIGURE 16-16 Pain transmission and the nociceptor. (A) Diagram showing the nociceptor and its environment. The nociceptor, represented anatomically as the terminal arborization of an afferent fiber, has its excitability influenced by physical stimuli and endogenous algesic substances. The action of these substances can also be indirect, operating on the microcirculation. Vanous substances, such as bradykinin, facilitate PG synthesis and can intensify the action of algesic substances. Analgesics can inhibit PGE synthesis, explaining part of their actions. (B) Diagram of the nociceptor and its environment and possible sympathetic mechanisms that may influence the excitability of the nociceptors. Sympathetic effer-ents can stimulate nociceptors when regulation is disturbed. Reproduced from Zimmerman, M. (1981). Triangle Sandoz J. Med. Sci. 20, 7. Copyright 1981, Pergamon, Ltd., London/NY.

Efferent sympathetic fiber

Release of noradrenaline can excite nociceptors directly, via contraction of smooth muscle, via the vasomotor system, and via release of algesic substances

FIGURE 16-16 Pain transmission and the nociceptor. (A) Diagram showing the nociceptor and its environment. The nociceptor, represented anatomically as the terminal arborization of an afferent fiber, has its excitability influenced by physical stimuli and endogenous algesic substances. The action of these substances can also be indirect, operating on the microcirculation. Vanous substances, such as bradykinin, facilitate PG synthesis and can intensify the action of algesic substances. Analgesics can inhibit PGE synthesis, explaining part of their actions. (B) Diagram of the nociceptor and its environment and possible sympathetic mechanisms that may influence the excitability of the nociceptors. Sympathetic effer-ents can stimulate nociceptors when regulation is disturbed. Reproduced from Zimmerman, M. (1981). Triangle Sandoz J. Med. Sci. 20, 7. Copyright 1981, Pergamon, Ltd., London/NY.

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