abstract: Synapses in the brain are composed of pre- and postsynaptic compartments, the latter often composed of dendritic spines. They make most of the synaptic excitatory connections, yet how their geometry modulates the voltage remains unclear. In this talk, I will focus on possible impacts of the synapse's geometry on its electrical properties, which are surprisingly not well understood on a basic level. I will use the dendritic spine as an example because it has a peculiar shape composed of a bulby head connected to a thin neck. I will present how, based on voltage imaging data and electro-diffusion modeling, it is possible to extract the spines' electrical properties that are not accessible experimentally yet. I will present a temporal deconvolution procedure for the genetically encoded voltage sensor expressed in hippocampal cultured neurons, and then, use electro-diffusion theory to compute the electric field and the current-voltage conversion.