Variability in spine shape and size. A. 3-dimensional reconstruction of a hippocampal dendrite (gray) illustrating different spine shapes including mushroom (blue), thin (red), stubby (green), and branched (yellow). PSDs (red) also vary in size and shape. Scale cube = 0.5 μm³. B. An example of a mushroom spine (blue) with a head diameter exceeding 0.6 microns and a narrow neck. C. An example of a thin spine (red) with a small head and narrow neck. D. An example of a stubby spine (green) with an equal head and neck diameter and an overall length that equals its width. E. An example of a branched spine (yellow) where both branches are thin spines. Scale bar = 0.5 μm and arrows indicate where the head and neck diameters were measured for each spine in B–E. F. A graph plotting the ratio of head diameters to neck diameters for the spines on the dendrite reconstructed in A. Mushroom spines (blue diamonds), stubby spines (green diamonds) and thin spines (red diamonds) segregated into distinct groups. Both branches of the branched spine were of a thin shape and are situated among the thin spine dimensions (yellow diamonds).