  The microscopic origin of the spin-orbit (SO) potential in terms of
sub-baryonic degrees of freedom is explored and discussed for application to
nuclei and hyper-nuclei. We thus develop a chiral relativistic approach where
the coupling to the scalar- and vector-meson fields are controlled by the quark
substructure. This approach suggests that the isoscalar and isovector density
dependence of the SO potential can be used to test the microscopic ingredients
which are implemented in the relativistic framework: the quark substructure of
the nucleon in its ground-state and its coupling to the rich meson sector where
the $\rho$ meson plays a crucial role. This is also in line with the Vector
Dominance Model (VDM) phenomenology and the known magnetic properties of the
nucleons. We explore predictions based on Hartree and Hartree-Fock mean field,
as well as various scenarios for the $\rho$-nucleon coupling, ranked as weak,
medium and strong, which impacts the isoscalar and isovector density dependence
of the SO potential. We show that a medium to strong $\rho$ coupling is
essential to reproduce Skyrme phenomenology in $N=Z$ nuclei as well as its
isovector dependence. Assuming an SU(6) valence quark model our approach is
extended to hyperons and furnishes a microscopic understanding of the quenching
of the $N\Lambda$ spin-orbit potential in hyper-nuclei. It is also applied to
other hyperons, such as $\Sigma$, $\Xi$ and $\Omega$.
