  The phonon-mediated attractive interaction between carriers leads to the
Cooper pair formation in conventional superconductors. Despite decades of
research, the glue holding Cooper pairs in high-temperature superconducting
cuprates is still controversial, and the same is true as for the relative
involvement of structural and electronic degrees of freedom. Ultrafast electron
crystallography (UEC) offers, through observation of spatio-temporally resolved
diffraction, the means for determining structural dynamics and the possible
role of electron-lattice interaction. A polarized femtosecond (fs) laser pulse
excites the charge carriers, which relax through electron-electron and
electron-phonon coupling, and the consequential structural distortion is
followed diffracting fs electron pulses. In this review, the recent findings
obtained on cuprates are summarized. In particular, we discuss the strength and
symmetry of the directional electron-phonon coupling in Bi2Sr2CaCu2O8+\delta
(BSCCO), as well as the c-axis structural instability induced by near-infrared
pulses in La2CuO4 (LCO). The theoretical implications of these results are
discussed with focus on the possibility of charge stripes being significant in
accounting for the polarization anisotropy of BSCCO, and cohesion energy
(Madelung) calculations being descriptive of the c-axis instability in LCO.
