  The enigmatic charged states $Z_c(3900)$, $Z_c(4020)$, $Z_c(4050)$,
$Z_b(10610)$, and $Z_b(10650)$ are studied within a coupled-channel
Schr\"odinger model, where radially excited quark-antiquark pairs, with the
same angular momenta and isospin as the $a_1(1260)$ and $b_1(1235)$, are
strongly coupled to their Okubo-Zweig-Iizuka - allowed decay channels
$D\bar{D}^*+\bar{D}D^*$ and $D^*\bar{D}^*$, or $B\bar{B}^*+\bar{B}B^*$ and
$B^*\bar{B}^*$, in $S$ and $D$-wave. Poles, matching the experimental mass and
width of all the above states, are found by varying only two free parameters.
From the wave-function analysis of each resonance, the probability of each of
the components contributing to the coupled system is estimated, and predictions
can be made for the relative decay fractions among the coupled open-charm or
open-bottom decay channels.
