Fig. 18.104.22.168. Polyribosomes (open arrow) associated with endoplasmic reticulum at the base of a dendritic spine (S). Microtubules (paired arrows) are evident in dendrites (D) but not in dendritic spines. The cytoskeleton of the spine is supported by actin microfilaments, evident in the spine neck (small arrow). Scale = 200 nm. (Rat, hippocampus.) Download the high resolution image.