Baroreceptors

Baroreceptors (or archaically, pressoreceptors) are sensors located in the blood vessels of all vertebrate animals. They sense the blood pressure and relay the information to the brain, so that a proper blood pressure can be maintained.

Baroreceptors are a type of mechanoreceptor sensory neuron that is excited by stretch of the blood vessel. Thus, increases in the pressure of blood vessel triggers increased action potential generation rates and provides information to the central nervous system. This sensory information is used primarily in autonomic reflexes that in turn influence the heart cardiac output and vascular smooth muscle to influence total peripheral resistance. Baroreceptors act immediately as part of a negative feedback system called the baroreflex, as soon as there is a change from the usual mean arterial blood pressure, returning the pressure toward a normal level. These reflexes help regulate short-term blood pressure. The nucleus tractus solitarii in the medulla oblongata of the brain recognizes changes in the firing rate of action potentials from the baroreceptors, and influences cardiac output and systemic vascular resistance.

Baroreceptors can be divided into two categories based on the type of blood vessel in which they are located: high-pressure arterial baroreceptors and low-pressure baroreceptors (also known as cardiopulmonary or volume receptors).

Arterial baroreceptors are stretch receptors that are stimulated by distortion of the arterial wall when pressure changes. The baroreceptors can identify the changes in both the average blood pressure or the rate of change in pressure with each arterial pulse. Action potentials triggered in the baroreceptor ending are then directly conducted to the brainstem where central terminations (synapses) transmit this information to neurons within the solitary nucleus. Reflex responses from such baroreceptor activity can trigger increases or decreases in the heart rate. Arterial baroreceptor sensory endings are simple, splayed nerve endings that lie in the tunica adventitia of the artery. An increase in the mean arterial pressure increases depolarization of these sensory endings, which results in action potentials. These action potentials are conducted to the solitary nucleus in the central nervous system by axons and have a reflex effect on the cardiovascular system through autonomic neurons.Hormone secretions that target the heart and blood vessels are affected by the stimulation of baroreceptors.

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