the cytoskeleton of dendritic spines is particularly important in their synaptic plasticity; without a dynamic cytoskeleton, spines would be unable to rapidly change their volumes or shapes in responses to stimuli. these changes in shape might affect the electrical properties of the spine. the cytoskeleton of dendritic spines is primarily made of filamentous actin (f-actin). tubulin monomers and microtubule-associated proteins (maps) are present, and organized microtubules are present. because spines have a cytoskeleton of primarily actin, this allows them to be highly dynamic in shape and size. the actin cytoskeleton directly determines the morphology of the spine, and actin regulators, small gtpases such as rac, rhoa, and cdc42, rapidly modify this cytoskeleton. overactive rac1 results in consistently smaller dendritic spines.