  We present the formalism for a new generation of unquenched quark models for
baryons in which the effects of quark-antiquark pairs (u anti-u, d anti-d and s
anti-s) are taken into account in an explicit form via a microscopic,
QCD-inspired, quark-antiquark creation mechaniscm. The present approach is an
extension of the flux-tube breaking model of Geiger and Isgur in which now the
contributions of quark-antiquark pairs an be studied for any initial baryon and
for any flavor of the q anti-q pair. It is shown that the inclusion of q anti-q
paris leads to a large contribution of orbital angular momentum to the proton
spin.
