  There is evidence that the distribution of suspected cosmic ray sources are
associated with the spiral arm structure of galaxies. It is yet not clearly
understood what effect such a cosmic ray source distribution has on the
particle transport in our Galaxy. We use the PICARD code to perform
high-resolution 3D simulations of electrons and protons in galactic propagation
scenarios that include four-arm and two-arm logarithmic spiral cosmic ray
source distributions with and without a central bar structure as well as the
spiral arm configuration of the NE2001 model for the distribution of free
electrons in the Milky Way. Results of these simulation are compared to an
axisymmetric radial source distribution. Also, effects on the cosmic ray flux
and spectra due to different positions of the Earth relative to the spiral
structure are studied. We find that high energy electrons are strongly confined
to their sources and the obtained spectra largely depend on the Earth's
position relative to the spiral arms. Similar finding have been obtained for
low energy protons and electrons albeit at smaller magnitude. We find that even
fractional contributions of a spiral arm component to the total cosmic ray
source distribution influences the spectra on the Earth. This is apparent when
compared to an axisymmetric radial source distribution as well as with respect
to the Earth's position relative to the spiral arm structure. We demonstrate
that the presence of a Galactic bar manifests itself as an overall excess of
low energy electrons at the Earth. Using a spiral arm geometry as a cosmic ray
source distributions offers a genuine new quality of modelling and is used to
explain features in cosmic ray spectra at the Earth that are else-wise
attributed to other propagation effects. We show that realistic cosmic ray
propagation scenarios have to acknowledge non-axisymmetric source
distributions.[Abbreviated]
