The bicep is a two-headed muscle in the upper arm. Both heads begin on the shoulder-blade and join to form a single muscle which is attached to the upper forearm. The muscle crosses both the shoulder and elbow joints and its main function is to flex the elbow.
The biceps brachii muscle gave all other muscles in the body their name. This comes from the Latin “musculus” which means “little mouse”. This is because the appearance of a flexed biceps looks like the back of a mouse.
The biceps muscle has two anchor points in the shoulder region. This is where the tendon is attached to the shoulder socket. It exits the joint trough the biceps groove and is attached to the long head of the muscle. The short head of the biceps is a continuation of the conjoined tendon which begins at the front of the shoulder-blade.
The illustration below shows a cross-section of the upper forearm. As you can see the biceps not only contains muscle fiber but also consists of blood vains to feed the bicep with energy needed for contraction and nerves. Their are two types of nerves present in the human body:
Sensory nerves: These conduct information from receptors to the central nervous system where the information is then processed (these nerves are responsible for sense).
Motor nerves: These conduct the signals from the central nervous system to the bicep. This will react in muscle contraction of the biceps.
A biceps, like all muscles, consists out of small fibers and are surrounded by endomysium. These fibers are grouped into one small muscle bundle that is surrounded by connective tissue (perimysium. These muscles bundles are again united into larger bundles called fascicles. The bundles are then grouped together to form muscle, which is enclosed in a sheath of epimysium. This muscle bundle is then enclosed by connective tissue called fascia. The muscle is connected to the bone by the tendon.
Each muscle fiber has thread-like protein strands called myofibrils that consist out of the contractile protein myosin (thick filaments) and actin (thin wires) contain. The effects of these are very important for the muscle to contract. The ability of a muscle to contract is determined by the building of the muscle, the extent of the cross section, the fiber length and the number of fibers within the muscle. Heredity determines the number of fibers in the muscles and training has no influence here. Although exercise does, however, affect other variables. Regular exercise increases the thickness of the muscle fibers, which in turn both increase muscle size and contractile force.
As mentioned before, in muscle contraction there are two contractile proteins, actin and myosin, that are responsible for a series of events. These are known as the “sliding filament model” of muscle contraction. A muscle fiber is composed of very small fibrils (myofibrils) and contains very thin filaments (filamentous structures) which are arranged by a characteristic pattern. The muscle fibril is divided into sarcomeres by the transverse Z-lines. The sarcomere is the basic unit responsible for the contraction in the muscle fiber. When a muscle fiber contracts, all sarcomeres contract simultaneously. The force is than transmitted to the fiber ends.
