Of the particles that make up an atom, only the electron is an elementary particle. Protons and neutrons are each made of 3 quarks, which makes them composite particles, particles that are made of other particles. The quarks are bound together by the gluons. The nucleus has boson pion fields responsible for the strong nuclear force binding protons and neutrons against the electrostatic repulsion between protons. Such virtual pions are composed of quark antiquark pairs again held together by gluons.