Regulation of Heart
The number of electrical impulses initiated by the SA node is primarily the result of its innervation by fibers from both sympathetic and parasympathetic branches of the autonomic nervous system. Sympathetic branch have a positive chronotropic effect (increase in rate) while parasympathetic branch have a negative chronotropic effect (decrease in rate). Parasympathetic innervations occurs by way of the vagus nerve. Sympathetic nerve fibers, when stimulated release norepinephrine at the nerve endings and comprise what is called the adrenergic system.
The central nervous system regulate the heat through the cardiac center in medulla and the hypothalamous.