Final answer:
In cases of low blood pressure, the vasomotor nerve activates the nucleus tractus solitarius, causing the release of neurotransmitters like epinephrine and norepinephrine that bind to adrenergic receptors and increase blood pressure by enhancing heart rate and vascular resistance.
Step-by-step explanation:
When blood pressure is hypotensive, the vasomotor nerve signals the nucleus tractus solitarius. This then releases certain neurotransmitters which bind to adrenergic receptors resulting in increased HR (heart rate), preload, contractility, BP (blood pressure), and vascular resistance.
Decreased firing rates of baroreceptors indicate falling blood volume/pressure, which triggers the cardiovascular centers to stimulate sympathetic responses like the release of epinephrine and norepinephrine by the adrenal glands. These catecholamines bind to adrenergic receptors on the vascular smooth muscles, causing vasoconstriction and increasing heart rate, which elevates blood pressure. Additionally, actions like the release of Antidiuretic Hormone (ADH) contribute to the increase in blood volume and pressure by promoting water reabsorption in the kidneys and constricting peripheral vessels.