Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:Phase 2 is a cessation of firing that is generated by premotor inhibitory synaptic events local to each abdominal ganglion and intrinsic spike frequency adaptation of the motoneurons (Chapple and Krans 2004; Krans and Chapple 2005).
Category: