  The recently discovered $P_c(4380)^+$ and $P_c(4450)^+$ states at LHCb have
masses close to the $\bar D\Sigma_c^*$ and $\bar D^*\Sigma_c$ thresholds,
respectively, which suggest that they may have significant meson-baryon
molecular components. We analyze these states in the framework of a constituent
quark model which has been applied to a wide range of hadronic observables,
being the model parameters, therefore, completely constrained.
  The $P_c(4380)^+$ and $P_c(4450)^+$ are studied as molecular states composed
by charmed baryons and open charm mesons. Several bound states with the proper
binding energy are found in the $\bar D\Sigma_c^*$ and $\bar D^*\Sigma_c$
channels. We discuss the possible assignments of these states from their decay
widths. Moreover, two more states are predicted, associated with the $\bar
D\Sigma_c$ and $\bar D^* \Sigma_c^*$ thresholds.
