  We study the response of the nucleon, as a system of three bound
(constituent) non relativistic quarks, to external (quasi static) electric and
magnetic fields. The approach, based on a sum rule technique, is applied to a
large class of two and three-body interquark potentials. Lower and upper bounds
to the electric polarizability and para-magnetic susceptibility are explicitly
calculated within a large variety of constituent models and their values
related to the features of the interquark interaction picture. The r\^ole of
three-body forces is investigated in details as well as the effects of SU(6)
breaking terms in the potential model. Our results can be used to extract the
mesonic contributions to the static polarizabilty and susceptibility. The quark
degrees of freedom give a quite sizeable contributions to both and the meson
cloud accounts roughly for 30% and 60% of the electric proton and neutron
polarizability respectively. The quark contribution to the paramagnetic
susceptibility is even higher and the mesonic effects are rather uncertain.
