Partial reconstruction of adjacent axonal boutons (triangle, square) synapsing with two dendritic spines (s1,s2) from the same parent dendrite ( den1) and with one dendritic spine from a different dendrite (den2). One bouton is an MSB (triangle) synapsing with a thin spine (s1) and one head of a branched spine (b1) arising from the second dendrite. Both dendrites are dark blue, all spines are a lighter blue, axon segments are white, and one postsynaptic density visible on branch 2 (b2) is yellow.