The Autonomic Nervous System in Body Protection and Pain

The autonomic nervous system is not only involved in the regulation of various target organs related to regulation of cardiovascular system, body core temperature, gastrointestinal tract, pelvic organs etc. but has functions that are conceptually best described in the context of regulating the protection of body tissues during ongoing challenges from within the body or from the environment. Responses of the organism during these challenges involve autonomic, neuroendocrine and somatic motor systems, the corresponding afferent (neural, hormonal and humoral) feedbacks from the body tissues and the representations of these motor and afferent systems in the central nervous system. These systems serve to adapt organ functions to the changing behavior and the behavior to changing threatening environments. The coordinated responses shown by the organism are states of the organism that are represented in the brain preparing the organism to generate the appropriate responses against threatening events. Autonomic responses, endocrine responses, somatomotor responses and interoceptive body sensations occur principally in parallel and are therefore parallel read-outs of these central representations. The central representations receive neuronal afferent, hormonal and humoral signals that monitor continuously the mechanical, thermal, metabolic and chemical states of the tissues. Control of the protective body reactions (including inflammation and hyperalgesia) by the CNS are integral components in this scenario and require autonomic, in particular sympathetic, systems which function in a differentiated way. During real or impending tissue damage the integrated protective systems are activated by the brain leading to illness responses including pain, hyperalgesia and other adverse body sensations.