Myelin, which insulates peripheral nerve axons, is unusual because it contains only:

1. Membranes differ widely in how much of their mass is protein rather than lipid. 2. An insulating membrane needs lipid, not machinery. 3. Myelin contains only 18 percent protein and 76 percent lipid. 4. 76 percent is the trap here: that is myelin's lipid share, and also the protein share of the mitochondrial inner membrane. _Source: OpenStax Biology for AP(R) Courses (CC BY 4.0), Ch 5 'Structure and Function of Plasma Membranes', sections 5.1-5.4_