  The nematic state of the iron-based superconductors is studied in the undoped
limit of the three-orbital ($xz$, $yz$, $xy$) spin-fermion model via the
introduction of lattice degrees of freedom. Monte Carlo simulations show that
in order to stabilize the experimentally observed lattice distortion and
nematic order, and to reproduce photoemission experiments, {\it both} the
spin-lattice and orbital-lattice couplings are needed. The interplay between
their respective coupling strengths regulates the separation between the
structural and N\'eel transition temperatures. Experimental results for the
temperature dependence of the resistivity anisotropy and the angle-resolved
photoemission (ARPES) orbital spectral weight are reproduced by the present
numerical simulations.
