We have studied the dynamics of defects (disclinations and walls) which appear in a thin nematic cell with planar anchoring, after a quench from the isotropic phase. The transient texture can be analyzed in terms of +/- 1/2 disclinations and surface pi-walls (corresponding to a pi-rotation of the director in the plane of the cell). We determine the structure of the walls and explain the main features of the dynamics. The relaxation of the texture is largely dominated by surface effects, which control the relaxation trajectories and velocities of the disclinations, as well as the dynamics of pi-walls.