Meat Science

MYOFIBRILS

• Myofibrils are long thin, cylindrical rods, bathed by the sarcoplasm and usually 1-2 µm in diameter.
• A muscle fibre with a diameter of 50 µm from meat animals will have at least 1000 and could have as many as 2000 (or more) myofibrils.
• On microscopic examination, the myofibrils present an appearance of alternating light and dark bands.
• A cross-section of myofibrils reveals a well-ordered array of dots of two distinct sizes. These dots are actually the myofilaments with different sizes corresponding to the thick and thin filaments of the myofibril.
• The thin filaments are almost all completely made up of a protein actin (actin filaments) , while the protein myosin (myosin filaments) is the sole constituent of the thick filaments.

• In longitudinal section, the thick filaments are aligned parallel to each other and are arranged in exact alignment across the entire myofibril. Similarly, the thin filaments are exactly aligned across the myofibril, parallel to each other and to the thick filaments.
• This arrangement of the myofilaments, and the fact that the thick filaments overlap in certain regions along their longitudinal axes, accounts for the characteristic banding or striated appearance of the myofibril.
• This banding effect, which takes the form of alternate light and dark areas, explains the use of the term striated muscle to describe skeletal muscle.
• The long axis of myofibrils in most muscles and in all mammals is parallel to the length of the muscle and extends the entire length of the muscle fibre.