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Receiver functions are a useful tool to infer the topography of Earth's discontinuities that define the transition zone. Ray theory and an assumed planar incoming wave are often used to estimate which regions contribute to the observations. We tested the validity of these simplifying assumptions on synthetic teleseismic receiver functions by calculating their adjoint sensitivity kernels for seismic velocity and boundary topography on the 660-and 410-discontinuities using P660s-and P410s-phases. We observed a strong mantle P-wave sensitivity:(i) associated with the Fresnel zone of the Pds-phase from source to conversion,(ii) forward scattering of the direct P wave and (iii) other phases that arrive in the Pds window. The sensitivity to S-wave velocity is predominantly limited to the Fresnel zone of the converted phase after conversion and to scatterers of the direct S-wave. The boundary topography kernels demonstrate …