Large veins called the venous sinuses help to drain fluid from the brain and skull.Credit: Zephyr/Science Photo Library The brain’s sewerage system — a network of large veins embedded in a membrane close to the skull — does not contain passive vessels as it was once thought. The delicate brain is protected from physical damage and invading pathogens by three layers of membrane called the meninges. Large veins called the venous sinuses, which sit in the outermost membrane, help to drain fluid from the brain and skull, but their full range of activities has been unclear until now. In a study1 in mice and humans published in Nature today, researchers captured the venous sinuses pumping blood and cerebrospinal fluid. The vessels also continuously shuffled their cells around to accommodate for patrolling immune cells.…