2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/104552Effect of the quark intrinsic motion on the proton spin structure functions is demonstrated. It is shown, that the covariant version of the quark-parton model taking into account the orbital motion gives the consistent picture of the proton spin structure, which is based on the valence quarks. This picture is supported by the recent data, which indicate, that the spin contributions from the sea quarks and gluons are compatible with zero.6 pages, 1 figure, Presented at the Workshop Nucleon05, Frascati 12-14Oct. 2005High Energy Physics - Phenomenologytext