A drug tricks your carotid baroreceptors into firing constantly, as if arterial pressure were always high. What would you expect it to do to resting heart rate and blood pressure?

Lower them, since the brain reads high firing as high pressure

Raise them, since the receptors are highly active

Lower them, since the brain reads high firing as high pressure

🩸 Why don't you faint every time you stand up?

Stand up quickly and gravity yanks nearly a liter of blood down into your legs and belly. For a moment, less blood returns to your heart, so blood pressure to your brain should crash — and yet you stay conscious. The save comes from an automatic circuit called the baroreflex, one of the body's fastest homeostatic loops.

Tucked into the walls of your carotid arteries (in the neck) and the aortic arch are stretch sensors called baroreceptors. They don't measure pressure directly — they measure how much the artery wall is stretched. When pressure drops, the walls stretch less, so the baroreceptors fire fewer signals to the medulla in your brainstem.

Reading fewer signals as "pressure is falling," the medulla ramps up sympathetic nervous activity: it speeds the heart and tightens blood vessels, pushing pressure back up within a second or two. When this loop is sluggish — from dehydration, aging, or certain drugs — you get the head-rush of orthostatic hypotension. The counterintuitive twist is that less nerve firing is what triggers the body's biggest response.