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:Preterminal and terminal Schwann cells serve as a growth substrate that guides the nodal sprouts to the original endplates of denervated muscle fibers (Son and Thompson, 1995b; Koirala et al., 2000).
Category: