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:…α subunits that are required for L-AChR function at the NMJ but are also expressed in the nervous system (Fleming et al., 1997); (Culetto et al., 2004); (Eimer et al., 2007). unc-50 and unc-74 encode genes previously implicated in L-AChR maturation and are broadly expressed in muscles and neurons.
Category: