If one were examine any type of muscle cell at the molecular level, what one would find is some kind of structured array of very thin (nano-scale) chains of protein called myofilaments.
These are the smallest contractile elements in muscle tissue. There are two kinds of myofilaments: the thin actin filaments (~7 nm diameter), and the thicker myosin filaments (~16 nm diameter).
In the case of skeletal and cardiac muscle these filaments alternate many times in parallel to the axis of muscle contraction.
During muscle shortening, the job of myosin is to latch on to points along the actin filaments and pull them closer toward each other. During relaxation and muscle lengthening the gap between adjacent actin filaments increases.
The muscle cells that are responsible for contracting sphinctors, blood vessels, bronchioli, the iris, and providing gut motility are a bit different. These are called smooth muscle cells. Instead of having a regular array of filaments parallel to axis of force-generation, they are arranged irregularly in a sort of criss-cross fashion that 'squishes' the cell as it contracts.
A muscle fiber collectively describes the long, multi-nucleated muscle cells which make up a skeletal muscle. They are termed fascicles when they are in bundles.
A myofiber is a multi-nucleated single muscle cell.
Muscle cell ,
Organ
Long, thin sheets with multiple nuclei
There more thin filaments than thick filaments in smooth muscle. The ratio is of the thin to thick filaments in the smooth muscle is approximately 15:1.
thin filaments
Actin filaments
thick and thin bands (lines) of filaments.
Actin Filaments
The structure of muscle filaments - View diagram of the structure of muscle ... These two types of filament have different structures that enable then to work together. ... Thick filaments are formed from a protein called myosin which has important ...muscle filaments cause muscles to contract,
Interactions between actin and myosin filaments of the sarcomere are responsible for muscle contractions. The I bands contain only thin (actin) filaments, whereas the A bands contain thick (myosin) filaments.
ATP
Thick filaments are made of the protein myosin and thin filaments are made of the protein actin. Myosin and actin filaments are arranged to form and overlapping pattern which gives muscle tissue its striated appearance.
Muscle, fasicle, muscle fiber, myofibril, myofilament
muscle relaxation
the sacromere, contains two kinds of filaments.