  We study the magnetic excitations of undoped iron oxypnictides using a
three-dimensional Heisenberg model with single-ion anisotropy. Analytic forms
of the spin wave dispersion, velocities, and structure factor are given. Aside
from quantitative comparisons which can be made to inelastic neutron scattering
experiments, we also give qualitative criteria which can distinguish various
regimes of coupling strength. The magnetization reduction due to quantum zero
point fluctuations shows clear dependence on the c-axis coupling.
