Final answer:
β-adrenergic stimulation leads to an increase in the heart rate and myocardial contraction strength, known as a positive chronotropic and inotropic effect, respectively, and is mediated by sympathetic activation. In contrast, parasympathetic stimulation results in a decrease of these functions.
Step-by-step explanation:
β-adrenergic stimulation would cause an increase in SA node discharge which would increase heart rate. This is known as a positive chronotropic effect. It also increases the force of myocardial contraction (positive inotrope) and accelerates AV conduction time. Sympathetic stimulation causes peripheral arteriolar vasoconstriction.
Not surprisingly, sympathetic stimulation is a positive inotrope, triggering the release of norepinephrine (NE) at the neuromuscular junction from the cardiac nerves and stimulating the adrenal cortex to secrete epinephrine and NE. These substances bind to both alpha and beta receptors on the cardiac muscle cell membrane to increase metabolic rate and the force of contraction, leading to an increase in stroke volume (SV) and a smaller residual end-systolic volume (ESV) in the ventricles.
In contrast, parasympathetic stimulation releases acetylcholine (ACh) at the neuromuscular junction from the vagus nerve, hyperpolarizing the membrane and inhibiting contraction. This decreases the strength of contraction, stroke volume, and raises the end-systolic volume (ESV). Parasympathetic stimulation primarily affects the atria, reducing atrial kick, end-diastolic volume (EDV), preload, and the force of ventricular contraction. In the ventricles, stronger parasympathetic stimulation directly decreases the force of contraction.