Smooth endoplasmic reticulum is present in most neurons, although it is sometimes difficult to differentiate it from the rough ER owing to the disorderly arrangement of ribosomes. Ribosomes are not associated with these membranes, and the cisternae usually assume a meandering, branching course throughout the cytoplasm. In some neurons, the smooth ER is quite prominent, for example, in Purkinje cells. Individual cisternae of the smooth ER extend along axons and dendrites