Strapped into an economy seat as we fly across the country for the holidays, it’s hard not to appreciate life’s basic necessities — a cup of soda, a bag of pretzels, the relief of seeing “vacant” on the lavatory door. It’s also a good time to remember that the real protagonists in this story are your trillions of cells, each of whom has the same basic needs you have. Each muscle cell, for example, needs an oxygen supply, nutrients, a way to eliminate wastes, a command system telling it whether to contract (or just relax), and a physical attachment allowing it to work with the rest of the muscle. All of these things are provided by a thin sheath of connective tissue called the endomysium which surrounds each muscle cell. The endomysium, in effect, acts as a scaffolding to support the infrastructure of blood vessels and nerve cells that allow the muscle cell to function. What kind of airplane seat does a muscle cell occupy? Considering that the bloodstream keeps the cell supplied with a constant stream of goodies, I imagine it’s got to be a first-class seat.