baroreceptor

Baroreceptors are stretch-sensitive mechanoreceptors located primarily in the walls of the carotid sinus and the aortic arch. They form a key part of the arterial baroreflex, a rapid feedback system that helps maintain stable blood pressure by sensing changes in arterial wall stretch that reflect mean arterial pressure.

Afferent signals from the carotid sinus travel via the glossopharyngeal nerve (cranial nerve IX), while signals from the aortic arch travel via the vagus nerve (cranial nerve X). These impulses are relayed to the nucleus tractus solitarius in the medulla oblongata, where they are integrated with other autonomic inputs. The resulting output modulates autonomic tone through pathways involving the rostral ventrolateral medulla and other centers, adjusting heart rate, myocardial contractility, and peripheral vascular resistance through sympathetic and parasympathetic mechanisms.

If arterial pressure rises, baroreceptor firing increases, leading to decreased sympathetic outflow and increased parasympathetic activity. This produces a lower heart rate and reduced contractility, along with vasodilation, resulting in a drop in blood pressure. If pressure falls, baroreceptor firing decreases, which enhances sympathetic activity and reduces parasympathetic influence, increasing heart rate, contractility, and vasoconstriction to raise blood pressure.

Baroreceptors provide short-term regulation of blood pressure and are subject to resetting with chronic changes in pressure, such as sustained hypertension. Their sensitivity may decline with age or vascular disease, diminishing the reflex’s effectiveness. Dysfunction of the baroreflex can contribute to labile blood pressure, orthostatic hypotension, or certain forms of hypertension, and may be involved in clinical conditions such as carotid sinus hypersensitivity or baroreflex failure.