Technically the core consists of both UP (User plane) and CP (Control plane). In 4G this was MME (Mobility management entity) for CP and the S-GW and P-GW (Serving and packet gateway - which interfaces to the internet) for UP. In 5G this has been replaced with VNFs such as AMF and others for the CP and UPF (User plane function) for UP. The 5G core is truly distributed and designed from the base to have re-usable and third party VNFs with well defined (REST based) APIs so it is really a game changer.

The RAN (Radio access network) and core split is there since 2G, where the RAN in LTE is the ENB (E node B) and in 5G is the GNB (G node B).