The arm has a wide range of movements, they swing backward and forward in walking and running, and they can be folded across the chest or raised above the head. The shoulder forms a base for the arm with most of the upper arm muscles originating from this area. In the upper arm, the biceps and triceps are arranged to give the forearm power to thrust and bend. The two muscles join at the elbow and allow you to bend and straighten your arm and also rotate your wrist and hand. The forearm muscles transmit power to the wrist, hands, and fingers. A group of flexors and extensors controls the movements of the wrist, acting in conjunction with other muscles of the fingers, thumb, radius, and ulna. These sets of muscles allow the arm and wrist to bend (flexion) and straighten (extension) as well as move outward away from the body (abduction) and inward toward the body (adduction). Some of these muscles participate in more than one type of movement.
The biceps brachii (two-headed arm muscle) consists of the long head and the short head. It extends from the shoulder to the elbow and is the main flexor of the elbow joint. When working with other nearby muscles, it can also move the shoulder, since its upper ends are attached to the scapula (shoulder blade). In addition it can twist the lower arm so that the palm faces outward, a movement called supination. At the lower end, the biceps tapers into a flat, strong tendon that is firmly fixed to a bulge on the upper end of the radius. The biceps and the triceps work together to control the up and down movement of the forearm.
The brachialis is a slender, flat muscle that lies under the biceps along the front of the lower half of the humerus (upper arm bone) and in front of the elbow joint. This muscle protects the elbow, and helps flex (bend) and rotate the forearm.
The brachioradialis originates two-thirds of the way down the humerus (upper arm bone) between the triceps and the brachialis. The muscle begins wide and flat and twists toward the front of the arm as it descends. It then widens and flattens again before ending in a flat tendon, which inserts on the thumb side of the radius. Unlike most of the long tendons of the forearm, the tendon does not cross the wrist joint, but rather ends at the distal end of the radius. This muscle bends the forearm at the elbow. It does not assist in turning the forearm.
The coracobrachialis is a thick, rounded muscle. It is the smallest muscle in the upper arm region. This muscle is a somewhat superficial muscle and can be partially seen on the inside of the upper arm near the arm pit when the arm is raised. It runs alongside, but separate from, the short head of the biceps brachii. It flexes and adducts the arm at the shoulder joint.
The pronator teres is a short, round, deep arm muscle. It arises high on the humerus (upper arm bone), slightly higher than the flexor mass on the fore arm. The muscle ends in a flat tendon which inserts in the radius. This muscle pronates the forearm and assists in bending the elbow.
The anconeus is a small triangular muscle that lies just below the elbow joint and extends a fourth of the way down the forearm. It is located on the outer back corner of the elbow. It extends and stabilizes the elbow joint.
The extensor carpi radialis brevis is a short, wide, flattened muscle. It arises from the humerus (upper arm bone) and narrows into a long, flat tendon about two-thirds of the way down the arm. It lies between the extensor carpi radialis longus and the extensor digitorum along the outer surface of the radius. This muscle extends and radially deviates the hand at the wrist joint.
The extensor digitorum is a wide, lateral muscle group. It has a flat, fusiform belly that extends from the humerus (upper arm bone) and towards the lower half of the forearm and develops into four tendons that insert into the middle and distal phalanges of the fingers. It does not insert into the thumb. This muscle works to extend all the joints of the fingers. It also extends the wrist.
The flexor carpi ulnaris originates from two heads, one from the humerus and one from the ulna (forearm bone). It lies along the ulnar side of the forearm and works with the extensor carpi ulnaris to bend the hand at the wrist. If it continues to contract, it bends the elbow.
The triceps brachii (three-headed muscle) lies at the upper portion of the inside of the arm. It is the main extensor of the arm and is made up of three teardrop shaped heads: the long head, the lateral head, and the medial head. When working with other nearby muscles it can also move the shoulder, since its upper ends are attached to the scapula. The long head, the largest of the three heads, is attached to the scapula (shoulder blade) just below the rounded socket of the shoulder joint, and extends almost three-fourths of the way toward the front of the arm. The lateral head lies on the back and side of the upper arm. The medial head curves around the back of the humerus (upper arm bone) and is mostly covered by the long head. The lower end is attached to the flattened end of the ulna. The triceps brachii extend the forearm at the elbow joint. It works with the biceps brachii to control the up and down movement of the forearm.
The deltoid muscle is a thick triangular muscle which cups the shoulder joint. It is attached to the clavicle (collar bone) and scapula (shoulder blade) at its upper end, and to the shaft of the humerus (upper arm bone) at its lower end. The muscle is divided into three portions: an anterior (clavicular) portion, and acrominal (middle) portion, and a posterior portion. The posterior portion is located on the back of the shoulder. Almost any movement of your shoulder and upper arm involves the deltoid muscle. The anterior portion is used to raise the arm from the body and to lower it again. The acrominal portion is a powerful abductor and the posterior portion is used to move the arm backward.
The pectoralis major muscle is located at the front of the thoracic cage. It is a thick, fan-shaped muscle and is divided into two parts that begin at the armpit and cover most of the front of the chest. The upper, or clavicular, part is attached to the clavicle (collar bone). The lower, or sternocostal, is attached mainly to the sternum (breast bone) and costal cartilage. This muscle is used when you bring your arms across the chest, raise and lower the arms and to rotate the arms. The clavicular portion will raise the arm, while the sternocostal portion will pull it down.
The subscapularis is a large triangular shoulder muscle that lies on the front surface of the scapula (shoulder blade) in the concave area called the subscapular fossa. The muscle converges at its lower end into a tendon which inserts in the humerus (upper arm bone). This muscle rotates the head of the humerus when the arms are raised to prevent displacement. It is also used to move the arms forward and down.
The teres major is a short and thick, somewhat flattened muscle that extends from the scapula (shoulder blade) to the humerus (upper arm bone). This muscle creates part of the posterior wall of the armpit and helps adduct the arm. It also rotates the arm medially behind the back. The teres major tenses when the arm lies next to the body. When the arm is extended the teres major is stretched, becoming elongated and thinner.
The teres minor is a small, elongated muscle that runs from the scapula (shoulder blade) to the humerus (upper arm bone). It inserts in the humerus by a flat, thick tendon. It laterally rotates the arm and helps stabilize the shoulder joint by holding the head of the humerus in its socket.
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