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The sympathetic nervous system is responsible for priming the body for action, particularly in situations threatening survival. [16] One example of this priming is in the moments before waking, in which sympathetic outflow spontaneously increases in preparation for action.
The somatic nervous system directs all voluntary movements of the skeletal muscles, and can be sub-divided into afferent and efferent neuronal flow. The autonomic nervous system is divided primarily into the sympathetic and parasympathetic nervous systems with a third system, the enteric nervous system, receiving less recognition.
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.
The average flow rate at the mouth of the Amazon is sufficient to fill more than 83 such pools each second. The estimated global total for all rivers is 1.2 × 10 6 m 3 /s (43 million cu ft/s), [ 1 ] of which the Amazon would be approximately 18%.
This same sympathetic outflow is increased to the sinoatrial node in the atria, which causes increased heart rate/cardiac output. These cardiopulmonary receptors also inhibits vagal stimulation in the vasoconstrictor center of the medulla resulting in decreased release of angiotensin , aldosterone , and vasopressin .
The ability of baroreflex activation therapy to reduce sympathetic nerve activity suggests a potential in the treatment of chronic heart failure, because in this condition there is often intense sympathetic activation and patients with such sympathetic activation show a markedly increased risk of fatal arrhythmias and death. [citation needed]
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 ...
Autonomic dysreflexia (AD) is a potentially fatal medical emergency classically characterized by uncontrolled hypertension and cardiac arrhythmia. [2] [3] [4] AD occurs most often in individuals with spinal cord injuries with lesions at or above the T6 spinal cord level, although it has been reported in patients with lesions as low as T10. [5]