Spontaneous ER dynamics in dendritic spines. (A) Representative images of the same dendrite at two time points to show dynamic events at, (i) the level of spine volume and (ii) ER content of spines. Examples of expanding ER and shrinking ER are depicted by triangles and circles, respectively. Scale bar (applies to all panels): 5 μm. (B) Cumulative probability plot to compare spine distribution of ER + and ER- spines at t = 0 (K-S test, P < 0.01). (C) Cumulative probability plot of normalised spine volumes to compare the dynamics of ER + and ER- spines over a 10 min period. (D) A comparison of the proportion of growing, “stable” and shrinking ER + and ER- spines (Z test, P < 0.01 for shrinking). (E) Cumulative probability plot of ER content of spines at t = 0 and t = 10 min (K-S test, P < 0.001). (F) Cumulative probability plot of normalised ER to illustrate its dynamics over a 10 min period. (G) Changes in ER content for the three spine subgroups.