Directed cell movement: a biophysical analysis.

The directed movement or directed growth of a cell in a polar guiding field (such as an electric field, a concentration gradient of chemotactic active molecules, a necrotactic gradient induced by a lysed cell, etc.) can be characterized by two independent variables: the speed, nu, of the cell and its migration angle, phi. Here it is shown that the direction of migration is controlled by a cellular automatic controller. The automatic controller can be regarded as the framework for the directed movement or growth and it can be applied even when the physicochemical signals to which the cell is responding are unknown.