[en] The authors show that the observational data on galactic synchrotron radiation can be explained if there is a break in the electron spectrum at about 2 GeV. It is also shown that one can explain the occurrence of that break by carefully considering the time evolution of the high-energy electron spectrum in supernova remnants, taking into account synchrotron losses, adiabatic expansion and diffusive losses from the remnant. The model considered is also in agreement with the observed radio spectrum of Cas A and the decay rate of its flux density. (Auth.)