What happens to arterioles when nerve fibers release norepinephrine?

When nerve fibers release norepinephrine, it binds to alpha-adrenergic receptors on the smooth muscle cells of arterioles. This binding causes vasoconstriction, which is the narrowing of the blood vessels. As a result, the contractile tone of the arteriole walls increases, leading to a reduction in the diameter of these vessels. This vasoconstriction significantly increases vascular resistance, which can affect blood pressure and flow in the vascular system.

The physiological purpose of this action includes regulating blood flow to various tissue beds according to the body’s needs, particularly during stress responses, as vasoconstriction directs blood toward vital organs and away from less critical areas. This mechanism is crucial in maintaining blood pressure and ensuring that adequate blood supply is routed where it is most needed.