  We study the transformation properties of the electron states in crystals
with spin-orbit coupling, focusing primarily on the limitations of the
frequently used pseudospin-1/2 description of twofold degenerate Bloch bands.
Using the language of corepresentations of magnetic point groups, we construct
the Bloch bases across the Brillouin zone in a way which is consistent with all
symmetry requirements. This construction is applied to derive the effective
spin-orbit Hamiltonians in noncentrosymmetric crystals, known as the
generalized Rashba models, in both single-band and multiband cases.
