noun, plural: thick filaments
A type of myofilament that is made up of bipolar myosin II filaments, and is approximately 12-14 nm in diameter
Each myofibril of a muscle fiber is comprised of myofilaments. In striated muscle the myofilaments are arranged in repeating pattern units called sarcomeres. When viewed under the microscope the sarcomere appears as dark and pale bands. These bands are due to the arrangement of the myofilaments in the muscle fiber in a regular fashion. There are two main types of myofilaments, the thin filaments and the thick filaments. The thin filament is about 7-9 nm in diameter. In contrast, the thick filament is about 12-14 nm in diameter. The thick filament is made up of bipolar, elongated proteins called myosin. There are about 300-500 myosin molecules in a sarcomere and they are located at the center of the sarcomere. 1 A myosin molecule looks like two golf clubs intertwined, with the heads pointing out from the surface of the thick filament.2 The myosin tails bind together, forming the core of the thick filament. 1 The core is a central bare zone without projecting heads and formed from antiparallel arrays of LMM regions of the myosin heavy chains. Thick filaments will self assemble in vitro under the right ionic conditions.
1 Thick Filaments and Myosin in Skeletal Muscle Fibers. In Get Body Smart. Retrieved from 
2 Structure and Function of Skeletal Muscle. Retrieved from