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Arm is defined as the upper limb situated between the shoulder and the elbow joints. Anatomically, arm is a segment between the shoulder and the elbow, adapted for precise positioning of the hand, and engaged in many manipulative tasks. Bones and muscles of the arm are important for many daily activities, including motion, carrying of the weight, lifting things up, driving, etc. The upper extremities are crucial for many activities of daily living, and it is extremely important to keep them strong and flexible. Human arm is composed of numerous bones and muscles and each of them have their specific function. Here is a quick overview on this topic.

Arm bones

Human skeleton reveals that an arm is composed of numerous bones. The humerus is the bone of the arm that is joined with the scapula in the shoulder and with the ulna and radius below at the elbow.

Humerus is a long bone that is strong enough to allow lifting up to 140kg. However, this long bone is relatively thin, and it can be broken easily.Radius is one of two large bones in the forearm that extends from the lateral side of the elbow to the thumb side of the wrist. This bone is slightly curved, and its primary function relates to the wrist joint.

Ulna is also a large bone in the forearm that runs parallel with radius. It is located closer to the body and exceeds the radius in length and size. The ulna is mostly responsible for the elbow joint.

Arm muscles

The arm contains the medial intramuscular septum, which divides muscles in two separate compartments: the anterior and posterior compartments of the arm. These compartments hold muscles that are innervated by the same nerve.

The anterior compartment of the arm is mostly concerned by flexion, and it contains three groups of muscles biceps brachii, brachialis, and coracobrachialis. All of these muscles allow bending, which is performed by decreasing the joint angle. Bones and muscles in the arm work together to move the joint in the flexed position and, for example, move the hand in the shoulder-level.

Posterior compartment of the arm includes triceps brachii and anconeus muscle, which are mainly concerned with extension. The triceps brachii is a larger muscle with lateral, medial and middle head. The annconeus is a small muscle important whenever the elbow joint has to be stabilized during the movement. Together they are engaged in extension, which is a movement of the joint that results in enlarged angle between two bones or body surfaces at a joint. An example of this movement is strengthening of the arm.

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