Dural venous sinuses within the skull's protective membranes actively constrict and dilate through RAMP1-dependent smooth muscle control, contradicting their traditional characterization as passive blood drains. The superior sagittal sinus contains bifurcated chambers with specialized endothelial cells that dynamically open and close intercellular boundaries via RAMP2 signaling, creating controlled gateways between blood and immune-rich spaces. This represents a fundamental reconceptualization of how the brain's protective barriers function. The discovery positions dural sinuses as active immune surveillance hubs rather than simple drainage conduits, potentially explaining how the supposedly immune-privileged brain monitors and responds to threats. The RAMP2-mediated gating mechanism offers a novel therapeutic target for neuroinflammatory conditions, from multiple sclerosis to viral encephalitis. However, this mouse-based research requires human validation, and the clinical implications of manipulating these barriers remain unclear. The work challenges decades of assuming brain drainage systems are passive, suggesting instead they're sophisticated immune checkpoints that could be pharmacologically modulated to enhance or dampen neuroinflammation depending on therapeutic need.