Vigorous protrusive activity occurs around the free margins of a small group of Madin-Darby bovine kidney cells. Broad, flattened lamellipodia are the primary surface extensions formed by the cells, but occasionally small, narrow filopodia can be observed as well. The filopodia, like the lamellipodia, can be utilized for locomotion, but also often carry out sensory functions, serving as feelers that provide information about the environment to the main process of a cell.

The surface activity of the MDBK cells can seem erratic, with lamellipodia and filopodia often appearing and disappearing in unpredictable ways. During the high speed playback of time-lapse sequences, their activity appears to be very rapid and can generate a flickering-like sensation. The overall movement of cell surface protrusions (termed ruffling) is rearward, and any particles that adhere to their membranes eventually are carried toward the back of the cell.

The intracellular movements of mitochondria and other membrane-bound organelles can be observed during this live cell video. Found concentrated around the nucleus, mitochondria have a granular or threadlike appearance when observed with a light microscope. The name of the organelles, which was coined in the nineteenth century, was chosen to reflect this fact. The term stems from the Greek words mitos and khondrion, meaning “thread” and “granule,” respectively.