How can a protein tunnel form through the membrane?

Transmembrane proteins are integral proteins that span the membrane, extending from the inner surface to the outer surface. Most transmembrane proteins have long, spiral-shaped helical sections that group together in a cluster that forms a hydrophilic protein tunnel through the membrane.  

Protein tunnels are very selective and allow only certain types of molecules to pass through between the extracellular matrix and the cytosol or cytoplasm.  

Transmembrane proteins, also known as membrane channels, are formed by protein complexes that span the cell membrane, extending from the inner surface to the outer surface, connecting the extracellular matrix to the cytosol or cytoplasm.