Final answer:
The thick filaments within muscle are formed by the protein myosin. The primary component of thin filaments is the protein actin, along with tropomyosin and troponin.
Step-by-step explanation:
Actin has binding sites for myosin attachment and tropomyosin blocks these sites when the muscles are at rest. Thick filaments within muscle are formed by the protein myosin. Myosin molecules connect with each other to form the central region of a thick filament near the M line, while the heads align on either side where the thin filaments overlap. The primary component of thin filaments is the protein actin, along with tropomyosin and troponin. Actin has binding sites for myosin attachment, and tropomyosin blocks these sites when the muscles are at rest. Troponin consists of three subunits that are involved in regulating muscle contraction.