Question: what are the names for the two types of filament in a myofibril?
Answer: Structure. The filaments of myofibrils, myofilaments, consist of two types, thick and thin: Thin filaments consist primarily of the protein actin, coiled with nebulin filaments. Actin, when polymerized into filaments, forms the "ladder" along which the myosin filaments "climb" to generate motion.