Nuclei are bound together by a relation of solidarity. A sequence is a logical succession of nuclei bound together by a relation of solidarity. Sequences can be included in other, larger sequences, still on the 'functional' level. Actions is the level of characters. Characters in the narrative are classified, not in terms of psychological essences, but according to their participation in actions.
Actions often have two sides.
For instance 'Giving' has a Donor and a Receiver. Example of actions are desire, communication, struggle.