What Situation(s) activate the sympathetic nervous system?
The Sympathetic Nervous System The sympathetic nervous system is even more automatic and only exceptionally susceptible to any voluntary control. When the environmental temperature is raised on a hot summers day, the increased temperature initiates several automatic responses. Thermal receptors convey stimuli to sympathetic control centers of the brain from which inhibitory messages travel along the sympathetic nerves to the blood vessels of the skin resulting in dilatation of the cutaneous blood vessels, thereby greatly increasing the flow of blood to the surface of the body from where heat is lost by radiation from the surface of the body. Dilatation of the blood vessels in this way tends to lower the blood pressure and to promote oozing or transudation of the fluid from the capillaries which may result in swelling of the dependent limbs. Thus, fine adjustments in sympathetic control of vascular contraction and “tone” are required to prevent excessive vascular dilatation and undue re
