Skeletal muscle structure is the same regardless of its shape or location. Here we explain the terms you need to know to understand the structure of skeletal muscle.
The structure of skeletal muscle
In very simple terms, each muscle comprises bundles of muscles fibres which are made of bundles of myofibrils. Myofibrils divide along their length into Sarcomeres. Connective tissue runs through the muscles surrounding the various elements.
Let’s start at the outside and work inwards. An outer layer of connective tissue called the Epimysium surrounds the muscle itself.
The Epimysium protects the muscle from friction against other muscles and bones. It also continues at the end of the muscle forming the tendon (along with other connective tissues).
Looking at the cross-section of skeletal muscle structure we see bundles of fibres called Fasciculi. The Perimysium is another connective tissue surrounding the Fasciculi.
Each Fasciculi contains anywhere between 10 and 100 muscle fibres, depending on the muscle. For example, a large strong muscle, such as the Quadriceps would have a large number of fibers within each bundle. Smaller muscles such as those in the hand contain fewer fibres per Fasciculi.
Muscle fibres & skeletal muscle structure
The Endomysium surrounds each muscle fibre. It is another connective tissue that insulates each muscle fiber. Muscle fibers range from 10 to 80 micrometers in diameter and may be up to 35cm long.
Beneath the Endomysium and surrounding the muscle fibre is the Sarcolemma. This is the muscle fibres cell membrane. Beneath this is the Sarcoplasm, a gelatinous fluid containing gylcogen, fats, and mitochondria. Mitochondria is the cell’s powerhouse that produces energy.
Each muscle fibre itself contains cylindrical organelles called Myofibrils. These are the smallest Each muscle fiber contains hundreds to thousands of Myofibrils. Myofibrils are bundles of Actin and Myosin proteins that run the length of the muscle fiber. They are important for explaining how muscles contract.
A network of tubules and channels called the Sarcoplasmic Reticulum surrounds the Myofibril. It is here in the structure of skeletal muscle that we store Calcium. Calcium is important for explaining muscle contraction. Transverse tubules pass inwards from the Sarcolemma throughout the Myofibril, through which nerve impulses travel.
Each Myofibril breaks down into functional repeating segments called Sarcomeres. For more information on Sarcomeres and how muscles contract, take a look at sliding filament theory.