  The nature of the recently discovered $Z_c$ and $Z_b$ structures is
intriguing. Their charge forces its minimal quark content to be $Q\bar Q q\bar
q$ (where $Q=\{c,b\}$ and $q=\{u,d\}$). In this work we perform a molecular
coupled-channels calculation of the $I^G(J^{PC})=1^+(1^{+-})$ charm and bottom
sectors in the framework of a constituent quark model which satisfactorily
describes a wide range of properties of (non-)conventional hadrons containing
heavy quarks. All the relevant channels are included for each sector, i.e.: The
$D^{(\ast)}\bar D^{\ast}+h.c.$, $\pi J/\psi$ and $\rho\eta_c$ channels for the
$Z_c$ and $B^{(\ast)}B^{\ast}$ and $\Upsilon(nS)\pi$ ($n=1,2,3$) channels for
the $Z_b$ analysis. Possible structures of these resonances will be discussed.
