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PART 3 Integration and Control Systems

TABLE 16.3

Effects of the Sympathetic and Parasympathetic Divisions on Various Effectors

*Receptor subtypes are indicated. The receptors are α 1 - and α 2 -adrenergic, β 1 - and β 2 -adrenergic, nicotinic cholinergic (n), and muscarinic cholinergic (m). † Normally, blood flow increases through coronary arteries because of increased demand by cardiac tissue for oxygen (local control of blood flow is discussed in chapter 21).In experiments that isolate the coronary arteries, sympathetic nerve stimulation, acting through α -adrenergic receptors, causes vasoconstriction. The β -adrenergic receptors arerelatively insensitive to sympathetic nerve stimulation but can be activated by epinephrine released from the adrenal gland and by drugs. As a result, coronary arteries vasodilate. ‡ Contraction of the radial muscles of the iris causes the pupil to dilate. Contraction of the circular muscles causes the pupil to constrict (see chapter 15). § Decreased stimulation of alpha receptors by the sympathetic division can cause vasodilation of penile blood vessels, resulting in an erection.