FOCAL ADHESIONS

Areas of close apposition, and thus presumably anchorage points, of the plasma membrane of a fibroblast (for example) to the substratum over which it is moving. Usually 1 x 0.2 m m with the long axis parallel to the direction of movement; always associated with a cytoplasmic microfilament bundle that is attached via several proteins to the plasma membrane at an area of high protein concentration (this is noticeably electron-dense in electron micrographs). Focal adhesions tend to be characteristic of slow-moving cells.