 Dear students, in this topic we shall discuss the arterial baroreceptors in detail. The arterial baroreceptors are widely distributed in the arterial system of vertebrates. They sense and monitor the arterial blood pressure changes. They also contribute to the regulation of arterial blood pressure. There are two types of baroreceptors in vertebrates. In the central cardiovascular system of amphibians, reptiles and mammals, there are unmyelinated baroreceptors which respond to blood pressures higher than normal. That is, they respond to high blood pressures and initiate reflexes to reduce the arterial blood pressure. Their effect protects the animal from the damaging increase in blood pressure. In addition to the unmyelinated baroreceptors, mammals also have myelinated baroreceptors in the carotid sinus, in their aortic arch, in the subclavian artery, in the pulmonary arteries and in the wall of the right atrium. These myelinated baroreceptors respond to blood pressures which are below normal. They protect from the prolonged periods of reduced blood pressure. The aortic baroreceptors monitor blood pressure in the ascending aorta and respond by triggering aortic reflex which adjusts blood pressure in the systemic circuit. While the baroreceptors in carotid sinus are extremely sensitive and they trigger reflexes which maintain adequate blood flow to the brain. Now we shall discuss the working mechanism of baroreceptors. Baroreceptors are stimulated by the stretch of arterial wall due to rise in arterial pressure. When they are stimulated, they send nerve impulses to the medulla of the brain. When the baroreceptors send messages, it responds to bring blood pressure to normal levels by decreasing the cardiac output and causing widespread peripheral vasodilation which decreases the blood pressure. The baroreceptor in the right atrium is stimulated by the stretch of arterial wall due to rise in arterial pressure. The baroreceptor in the left atrium is stimulated by the stretch of arterial wall due to rise in arterial pressure.