the sds model was intended as a computationally simple version of the full baer and rinzel model. it was designed to be analytically tractable and have as few free parameters as possible while retaining those of greatest significance, such as spine neck resistance. the model drops the continuum approximation and instead uses a passive dendrite coupled to excitable spines at discrete points. membrane dynamics in the spines are modelled using integrate and fire processes. the spike events are modelled in a discrete fashion with the wave form conventionally represented as a rectangular function.