	In addition to their electrophysiological activity and their receptor-mediated activity, spines appear to be vesicularly active and may even translate proteins. Stacked discs of the smooth endoplasmic reticulum (SERs) have been identified in dendritic spines. Formation of this "spine apparatus" depends on the protein synaptopodin and is believed to play an important role in calcium handling. "Smooth" vesicles have also been identified in spines, supporting the vesicular activity in dendritic spines. The presence of polyribosomes in spines also suggests protein translational activity in the spine itself, not just in the dendrite.