Fig. 2. Diagram of the model sphincter: a two-dimensional system of point masses. (A) The masses were assumed to be interconnected by tensile elements (with zero cross-sectional area) thought to represent the circularly arranged muscle fibre bundles and the radially oriented connective tissue. (B) Detail of the shaded portion in A. The masses were connected to either four (corner point) or two (mid point) tensile elements, with the exception of the corner point masses on the inner or outer border, which are connected to only three tensile elements. The tensile elements were assumed to have a constant curvature along their length, as determined by the locations of two adjacent corner points and one intermediate mid point. Fluid elements were enclosed by the tensile elements through four corner points and four mid points. The pressure was assumed to be constant in any one element. The motion of the masses was calculated by application of Newton’s second law. The acceleration of each mass was calculated from the forces in the connecting tensile elements (red arrows) and the forces due to the pressure in the adjacent fluid compartments (blue arrows). (C) Mapping of the neurons in the neural network to the muscle elements in the sphincter. The neurons in the neural network (labelled a–j in the upper square) correspond to the muscle elements in the sphincter. The vertical columns of neurons innervate the circular layers of the muscle, starting from the outside, whereas the horizontal rows innervate the radial segments of the muscle, starting at the 09:00 h position and proceeding in a clockwise direction.
