part of endomembrane system dendritic spine membrane-bounded organelle spine apparatus pr cellular_component dense material GO:0097444 2012-12-06T14:05:58Z A specialization of the endomembrane system found in some classes of dendritic spines consisting of two or more closely apposed lamellae with interspersed electron dense material. The endomembrane component is continuous with the smooth endoplasmic reticulum. NIF_Subcellular:sao725931194