The biceps refers to the biceps brachii muscle. It is located in the upper arm in humans, but is also found in quadrupedal mammals (such as dogs). In both cases, it is responsible for, among other things, bending the arm or foreleg.
What characterizes the biceps brachii muscle?
The upper arm muscle, often referred to as the “two-headed muscle of the arm” or biceps for short, is a skeletal muscle that consists of two muscle heads. It is located on the upper or even front side of the upper arm and is responsible for flexing the arm. For this reason, it is also called the “arm flexor“. Basically, the two-headed thigh flexor muscle is also called the biceps. However, the name is more common with the upper arm muscle than with the biceps femoris muscle.
Anatomy and structure
The two-headed muscle of the arm is understood by medicine to be a skeletal muscle located in the upper arm. The biceps brachii muscle consists of two muscle heads: the caput longum (also known as the long head) and the caput breve (also known as the short head). These two heads are responsible for the naming of the muscle. In humans, they arise from the scapula. The two heads of the biceps join approximately where they become visible externally. Here they become a single muscle body or muscle belly. This muscle belly attaches below the crook of the elbow, directly at the muscle hump called the radial tuberosity of the radius (medically called the radius), along with a tendon of the humerus. This tendon passes in two ways into the aponeurosis musculi bicipitis (also called tendinous muscle origin) and into the fascia of the forearm (the fascia antebrachii). Unlike in humans, the biceps in quadrupedal mammals such as dogs, cats, and horses has only a single origin at the small bony tuberosity (tuberculum supraglenoidale) of the scapula. As a result, the biceps in this case also has only one head. From a comparative anatomical point of view, however, it is nevertheless titled in medicine as having two heads and thus also as biceps.
Function and tasks
The biceps is responsible for rotating the forearm from its basic position, so that the thumb rotates from the inside out and around the hand – until it is pointing vertically upward and in the opposite direction of the basic position. Anatomy refers to this function as supination. If the forearm is already in a supinated position, the biceps are able to bring it back to the original position. Another function of the biceps is to flex the forearm at the elbow. Both heads have their own tasks, which in detail affect the overall function of the biceps. The long head is used when the upper arm is to be lifted off or away from the chest. The short head is responsible for movement sequences in which the arm is to be guided toward the chest. In addition, both muscle heads act simultaneously on the movement sequence when the arm is to be guided away from the body and forward. However, the two heads are also necessary during internal rotation of the arm. Here they work together so that a smooth movement is produced. In addition, they also work together to ensure that the arm does not rotate too far. In this way, they prevent injuries. A difference in function can be found in the biceps again in the comparison between humans and animals – in quadrupedal mammals, the biceps act as a connection of the leg to the shoulder joint and is exclusively active as a flexor of the elbow. Rotational movements are not common in animals such as dogs, cats and horses and are therefore not intended. For this reason, the biceps is less strong and powerful in them. It is also somewhat weaker than the biceps of humans or other bipedal mammals.
Diseases and ailments
The most common ailment associated with the biceps in humans is biceps tendon rupture. In this rupture, the attachment tendon or the tendon of origin of the muscle usually ruptures. Another and similar injury can be a strain of the muscle. In most cases, both injuries result from trauma, as can happen in an accident. However, a rupture or strain of the biceps can also result from a short or even long-term overuse of the upper arm. In older people, a rupture or strain of the muscle often occurs as a result of age-related wear and tear.The muscle often weakens with age, making it more susceptible to injury. A disease of the biceps, on the other hand, is a pulley lesion. Medicine speaks of such a lesion when there is an unnatural displacement of the tendon of origin. Such a lesion usually occurs when the tendon shifts obliquely in the groove of the shoulder joint over time. This can happen, among other things, due to overuse, but also due to an accident. In rare cases, the tendon is already appropriately displaced at birth. Over time, displacement of the tendon causes it to thin out, making it more susceptible to injury. Often, the pulley lesion ends up rupturing the biceps tendon. For this reason, medical science also refers to it generically when there is a displacement-related injury to the tendon.
