[Criteria of the optimal functioning of large and small pial artery subsystems].

The geometrical parameters of the pial arterial systems were studied in total microscopic preparations of the pia mater of rabbits. The subsystem of the larger pial arteries (with the diameter over 100 microns) was shown to provide a blood transport with the minimum energy losses. On the other hand, in the subsystem of the smaller arteries (under 100 microns), the effective resistance should be relatively great under normal conditions, but when the blood supply to the brain tissue becomes diminished, the changes of their diameters provide the minimum energy loss. Hence, the main function of the larger pial arteries is the blood transport, while that of the smaller ones -- regulation of the blood supply intensity in respective cortical areas.