Efferent fibers of these autonomic nerves travel to the heart and blood vessels where they modulate activity of these target organs. The heart is innervated by vagal and sympathetic fibers.
Cardiac function is altered by neural activation.
Sympathetic and parasympathetic effects on heart function are mediated by beta-adrenoceptors and muscarinic receptors , respectively. Varicosities, which are small enlargements along the nerve fibers, are the site of neurotransmitter release. Capillaries are not innervated. Activation of vascular sympathetic nerves causes vasoconstriction of arteries and veins mediated by alpha-adrenoceptors . Parasympathetic fibers are found associated with blood vessels in certain organs such as salivary glands, gastrointestinal glands, and in genital erectile tissue.