Multistate models (MSMs) provide an in silico representation of complex molecules, specifying all the possible functional states of a molecule in a computationally tractable manner. This is achieved through the use of rule-based languages that look for only those properties necessary for a reaction to proceed. We have built a MSM that explores the major components of the excitatory postsynapse, focussing on the properties and states of AMPA receptors (AMPARs), and how these may change in plasticity events. Our understanding of how AMPARs are involved in plasticity, whilst rich in data and interpretation, lacks coherence. This is largely due to the necessarily piecemeal nature of experiments, which may only focus on a small part of the interactions AMPARs have within a dendritic spine. Our MSM avoids this issue by modelling all parts at once, based on experimentally-derived concentrations and kinetic parameters. “Early” or “initial” plasticity is thought to be protein synthesis independent, and arise from the difference in kinase and phosphatase activity on AMPARS induced by changes in calcium concentrations. Different experimental induction protocols alter dendritic spine calcium levels in different ways over time, with some achieving stronger or more long-lasting plasticity. We took several protocols and assessed how the model responded to each. We show a broadly good fit with LTP and LTD protocols to existing data, and that in most instances the driving force lies in the balance of phosphatase and kinase activity. Given the importance of enzymatic activity for successful plasticity, two commonly used sets of values for CaMKII binding to both calmodulin and PP1 were also assessed. The Li et al. (2008) values result in a slower reactivation of PP1 after LTP induction than those from the DOQCS database (Sivakumaram et al., 2003), and a smaller proportion of phosphorylated CaMKII for a given stimulus. The DOQCS values allow for a small chance that the potentiation seen can be maintained for over an hour by a modest random change in calcium concentrations post induction. No such capacity was seen when using the Li et al. vetalues. Our MSM reinforces the importance of the kinase:phosphatase ratio when determining the direction and maintenance of plasticity, but also warns that some parameter sets may lead to different conclusions on the mechanisms at play.