Objective: UPlanSApo 100x oil/1.40	Exposure: 350 ms
Microscope: Olympus DSU/IX81	Gain: 3
Camera: Hamamatsu ImagEM	Interval: 2 s

The endoplasmic reticulum is a network of flattened sacs and branching tubules that extends throughout the cytoplasm in plant and animal cells. These sacs and tubules are all interconnected by a single continuous membrane so that the organelle has only one large, highly convoluted and complexly arranged lumen (internal space). Usually referred to as the endoplasmic reticulum cisternal space, the lumen of the organelle often takes up more than 10 percent of the total volume of a cell. The endoplasmic reticulum membrane allows molecules to be selectively transferred between the lumen and the cytoplasm, and since it is connected to the double-layered nuclear envelope, it further provides a pipeline between the nucleus and the cytoplasm. In the digital video presented in this section, human osteosarcoma cells (U2OS line) expressing enhanced yellow fluorescent protein (EYFP) targeted to the endoplasmic reticulum were imaged with a Hamamatsu ImagEM camera system on a spinning disk confocal microscope.