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The upper arm is located between the shoulder and elbow joints and contains over 20 muscles that work together to help with big and small arm movements. The muscles in the upper arm help us move our arms, hands, fingers, and thumbs, allowing us to perform activities that require big movements, like swinging a baseball bat, and small, precise movements, such as writing our name. The upper arm muscles also enable us to straighten our elbows, raise our arms above our heads, or do push-ups. The biceps and triceps are well-known muscles in the upper arm, and their strength can be improved through exercises like bicep curls, tricep extensions, and bench presses. The triceps brachii, for example, has three muscle heads that work together to straighten the arm, which is essential for activities requiring pushing and pulling. The brachialis muscle lies deep to the biceps brachii and is responsible for flexion at the elbow. Additionally, the coracobrachialis, biceps brachii, and brachialis muscles in the anterior arm are innervated by the musculocutaneous nerve, which receives supply from nerve roots C5 to C7.
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Biceps brachii
The biceps brachii, commonly known as the biceps, is a large, thick muscle on the upper arm's ventral portion. It is composed of a short head and a long head. The long head is located on the lateral side of the biceps brachii, while the short head is located on the medial side. The biceps brachii works across three joints and is able to generate movements in the glenohumeral, elbow, and radio-ulnar joints.
The short head originates from the apex of the coracoid process of the scapula, while the long head originates from the supraglenoid tubercle of the scapula. Both heads course distally and become a confluent muscle belly before tapering across the anterior aspect of the elbow, inserting on the radial tuberosity and the fascia of the forearm via the bicipital aponeurosis. The biceps brachii is one of the chief muscles of the arm, and its origin at the scapula and insertion into the radius allow it to act on both the shoulder joint and the elbow joint.
The biceps brachii is involved in various tasks, including lifting, sports involving throwing and racket use, and gesturing. It is responsible for the flexion and supination (outward rotation) of the forearm. In the shoulder joint, the long head pulls the arm away from the trunk (abduction) and turns it inwards (inward rotation), while the short head pulls the arm back towards the trunk (adduction). When both heads contract simultaneously, it leads to an arm bend (flexion). In the elbow joint, the muscle bends the forearm (flexion) and rotates it outward (supination).
The biceps brachii is susceptible to various conditions, such as tendinopathy and tendinitis, often caused by muscle overuse, trauma, or repetitive activity. A rupture of the long head tendon can result in the "popeye deformity", where the muscle forms a ball at the anterior mid-arm.
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Brachialis
The brachialis is a muscle located in the upper limb of the body, specifically in the anterior (flexor) compartment of the arm, deep to the biceps brachii. It is one of four muscles in the upper arm, which is located between the shoulder and elbow joint. The other three muscles in the anterior compartment are the biceps brachii, coracobrachialis, and triceps brachii.
The brachialis is the primary flexor of the elbow, allowing for flexion at the elbow joint. It is the only pure flexor of the elbow joint, producing the majority of force during elbow flexion. This muscle is also responsible for flexing the forearm at the elbow joint, and it is not affected by pronation or supination of the forearm. The brachialis is a broad muscle, with its broadest part located in the middle, and it sometimes fuses with the fibres of the biceps brachii, coracobrachialis, or pronator teres muscles.
The brachialis muscle can be injured by repetitive forceful contractions or muscular contractions with the arm in hyperextension. This is commonly seen in climbers due to the pronation of the hand and the extended starting position. Physical activities that involve a lot of pull-ups, curls, and rope climbing can also cause brachialis muscle pain. A strain to the brachialis tendon can result in a lack of elbow extension due to painful end-range stretching of the tendon. This condition is known as brachialis tendonitis, and it is common in climbers.
To prevent injuries to the brachialis muscle, it is important to warm up before exercising and gradually increase the intensity of workouts. It is also recommended to avoid lifting heavy weights and to stop any activity that causes pain. If you experience muscle pain, numbness, severe muscle weakness, or swelling, it is important to seek medical advice.
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Coracobrachialis
The coracobrachialis is a long and slender muscle of the anterior compartment of the upper arm. It is one of three muscles in the anterior compartment, the other two being the biceps brachii and brachialis. The coracobrachialis is not one of the most prominent arm muscles, and it doesn't play a major role in moving the arm. However, it can become tight from certain activities and can be a hidden source of shoulder or arm pain.
The main function of the coracobrachialis is to produce flexion and adduction of the arm at the shoulder joint. It helps to bring the upper arm forward, like when shaking hands or taking something from someone. It also assists in bringing the arms back down to the sides from an "airplane" position. The coracobrachialis plays a supporting role in internal rotation, bringing the arms inward toward the body, and in shoulder stability, holding the upper arm bone within the shoulder socket during rotation.
The coracobrachialis muscle attaches to the front of the shoulder joint and the upper arm bone. It starts from the shoulder joint and inserts into the upper arm bone about halfway down, on the armpit side. It extends from the coracoid process of the scapula to the shaft of the humerus, with muscle fibres running inferolaterally toward the humerus. The muscle is located posterior to the pectoralis major muscle and anterior to the tendons of the subscapularis, latissimus dorsi, teres major, and the medial head of the triceps.
The coracobrachialis is innervated by the musculocutaneous nerve (C5-C7), a branch of the lateral cord of the brachial plexus. It receives its blood supply from the muscular branches of the brachial artery. A rupture of the coracobrachialis is extremely rare and almost only occurs in serious accidents. However, the muscle can be strained or injured, leading to weakness, soreness, or instability when using the arm for various activities such as lifting weights, pushing heavy doors, or reaching diagonally across the body.
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Triceps brachii
The triceps brachii is a three-headed muscle in the arm, with long, medial, and lateral heads. It is the only muscle in the posterior compartment of the arm, with the medial head lying deeper than the other two. The triceps brachii is innervated by the radial nerve, which gives off a separate branch for each head. The C6 root value of the radial nerve innervates the lateral head, root value C7 innervates the long head, and root value C8 supplies the medial head. However, recent studies have found that in some individuals, the long head of the triceps brachii is innervated by the axillary nerve, or by both the radial nerve and axillary nerve.
The triceps brachii is supplied with oxygen and nutrients from the branches of the deep brachial artery, specifically the superior ulnar collateral artery, which arises from the brachial artery. The medial head is also innervated by the ulnar nerve. The triceps brachii is involved in creating anatomical spaces traversed by neurovascular structures, making it an important surgical landmark.
The long head of the triceps brachii arises from the infraglenoid tubercle of the scapula, which is a rough area at the inferior margin of the glenoid fossa. It extends slightly above to the adjacent glenoid labrum and blends with the glenohumeral capsule of the shoulder joint, contributing to its stability. The superior portion of the long head is covered by the posterior border of the deltoid muscle. On its course, the long head descends through the wedge-shaped interval between the teres major and minor and the humerus, creating three distinct anatomical spaces.
The lateral head of the triceps brachii originates from a narrow, linear ridge on the posterior surface of the humerus, just superior to the radial groove. A portion of the muscle fibres also arise from the lateral intermuscular septum. Its attachment ascends obliquely, beginning from the lateral border of the humerus behind the deltoid tuberosity. The medial head arises proximally in the humerus, just inferior to the groove of the radial nerve, from the dorsal surface of the humerus, and from the medial intermuscular septum.
The triceps brachii can be exercised through isolation or compound elbow extension movements, or through static contraction to keep the arm straight against resistance. Isolation exercises include cable push-downs, lying triceps extensions, and arm extensions behind the back. Examples of compound exercises include pressing movements like push-ups, bench presses, and dips. Static contraction movements include pullovers, straight-arm pulldowns, and bent-over lateral raises.
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Forearm muscles
The forearm is the section of the upper limb between the elbow and the wrist. The forearm muscles are supported by two bones, the ulna and radius, which form a joint that rotates to let you turn your palm up or down. The forearm muscles are divided into two compartments: the anterior (flexor) compartment and the posterior (extensor) compartment. There are 20 muscles in the forearm that act on the elbow and wrist joints, as well as the carpometacarpal, metacarpophalangeal, and interphalangeal joints of the hand.
The anterior compartment has three layers of muscle: superficial, intermediate, and deep. The superficial muscles in the anterior compartment are the flexor carpi ulnaris, palmaris longus, flexor carpi radialis, and pronator teres. The flexor carpi ulnaris lets you move your wrist back and forth. The palmaris longus helps flex the wrist, while the flexor carpi radialis helps move your arm away from your body. The pronator teres muscle works to rotate the forearm. The flexor digitorum superficialis is the only muscle in the intermediate layer. It flexes the metacarpophalangeal joints and proximal interphalangeal joints at the four fingers, and flexes at the wrist. There are three muscles in the deep anterior forearm: flexor digitorum profundus, flexor pollicis longus, and pronator quadratus. The pronator quadratus is a square-shaped muscle that lets you turn your forearm downward.
The extrinsic muscles, which are found in the posterior compartment, help extend the digits of the hand. The brachioradialis muscle allows you to bend your elbow and turn your arm. The extensor carpi radialis longus and extensor carpi radialis brevis extend your wrist and move your hand away from the direction of your thumb. The extensor digitorum splits into four tendons and connects to the finger joints, helping to straighten or extend the fingers. The supinator muscle allows you to supinate your forearm, which means to turn it so that your palm faces up. The extensor pollicis brevis allows you to make a thumbs-up signal, while the extensor pollicis longus extends the thumb.
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Frequently asked questions
The upper arm contains four muscles – three in the anterior compartment (biceps brachii, brachialis, coracobrachialis), and one in the posterior compartment (triceps brachii).
The biceps brachii is involved in flexion at the elbow, allowing you to bring your hand to your ear. It is also important for positioning your arm and hand, weight-bearing, and pushing and pulling.
The triceps brachii has three heads that work together to straighten the arm. This is important for activities requiring pushing and pulling, and it also allows you to bear weight on your hands, wrists, and arms.
The brachialis lies deep to the biceps brachii and forms the floor of the cubital fossa. It is also involved in flexion at the elbow.
The coracobrachialis, along with the biceps brachii and brachialis, receives motor innervation from the musculocutaneous nerve. It helps with precise movements, such as threading a needle, and big movements like throwing a ball.
