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The sympathetic nervous system's primary process is to stimulate the body's fight or flight response. It is, however, constantly active at a basic level to maintain homeostasis. [4] The sympathetic nervous system is described as being antagonistic to the parasympathetic nervous system.
The sympathetic nervous system (nerves dominant during the body's fight-or-flight response) increase heart rate (positive chronotropy), by decreasing the time to produce an action potential in the SAN.
The white ramus communicans (pl.: rami communicantes) from Latin ramus (branch) and communicans (communicating) is the preganglionic sympathetic outflow nerve tract from the spinal cord. Each of the thoracic, and the first and second lumbar nerves contribute a white ramus communicans to the adjoining sympathetic ganglion , unlike the gray rami ...
The sympathetic division emerges from the spinal cord in the thoracic and lumbar areas, terminating around L2-3. The parasympathetic division has craniosacral "outflow", meaning that the neurons begin at the cranial nerves (specifically the oculomotor nerve, facial nerve, glossopharyngeal nerve and vagus nerve) and sacral (S2-S4) spinal cord.
This stimulates an afferent limb which activates central nervous system pathways that in turn exert two different but synergistic autonomic effects on the body. First, global sympathetic outflow is reduced and, second, vagal outflow is increased.
This is set in motion via the adrenergic (sympathetic) outflow from the brain, but the heart is unable to meet requirements because of the low blood volume, or decreased return. A feedback response to the medulla is triggered via the afferent vagus nerve. The high (ineffective) sympathetic activity is thereby modulated by vagal (parasympathetic ...
Beginning in the sympathetic nervous system, an external stimulus affects the adrenal medulla and causes a release of catecholamines. The sympathoadrenal system is a physiological connection between the sympathetic nervous system and the adrenal medulla and is crucial in an organism's physiological response to outside stimuli. [1]
In vivo sympathetic outflow within the myocardium is probably best described by the time honored description of the sinoatrial tree branching out to Purkinges fibers. Parasympathetic inflow within the myocardium is probably best described by influence of the vagus nerve and spinal accessory ganglia. [citation needed]