Maximus Gage
The forearm is the section of the upper limb that extends from the elbow to the wrist, with its bony structure formed by the radius and ulna. The forearm contains twenty muscles that act on the elbow and wrist joints, as well as the carpometacarpal, metacarpophalangeal, and interphalangeal joints of the hand. These muscles enable complex movements of the arm, wrist, and fingers. The forearm muscles can be divided into four groups: flexors, extensors, pronators, and supinators. The triceps brachii and anconeus are extensors that extend the forearm at the elbow joint. The supinator muscle, located in the deep region of the forearm posterior compartment, is responsible for supination, or turning the forearm so that the palm faces upwards.
| Characteristics | Values |
|---|---|
| Muscles that extend the forearm | Triceps Brachii, Anconeus |
| Muscles that flex the forearm | Biceps Brachii, Brachialis, Brachioradialis |
| Muscles that pronate the forearm | Pronator Teres, Pronator Quadratus |
| Muscles that supinate the forearm | Supinator |
| Muscles that extend the wrist | Extensor Carpi Radialis Longus, Extensor Carpi Radialis Brevis, Extensor Digitorum, Extensor Carpi Ulnaris |
| Muscles that flex the wrist | Flexor Carpi Radialis, Palmaris Longus |
| Muscles that extend the fingers | Extensor Digitorum, Extensor Digiti Minimi, Extensor Indicis |
| Muscles that extend the thumb | Extensor Pollicis Longus, Extensor Pollicis Brevis |
| Muscles that abduct the thumb | Abductor Pollicis Longus |
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What You'll Learn
Triceps Brachii
The triceps brachii is a three-headed muscle of the arm. It is the only constituent of the posterior muscle group of the arm, spanning almost the entire length of the humerus. The triceps brachii consists of a long, medial, and lateral head, which originate from their respective attachments on the humerus and scapula and insert via a common tendon on the ulna. The main function of the triceps brachii is the extension of the forearm at the elbow joint.
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, the C7 root value innervates the long head, and the C8 root value supplies the medial head. However, recent studies have observed that in around 14% of individuals, the long head of the triceps brachii is innervated by the axillary nerve, and in 3% it receives dual innervation from both the radial nerve and axillary nerve. The triceps brachii is supplied with oxygen and nutrients from the branches of the deep brachial artery.
The long head arises from the infraglenoid tubercle of the scapula, which is a rough area at the inferior margin of the glenoid fossa. Its attachment extends slightly above to the adjacent glenoid labrum and blends with the glenohumeral capsule of the shoulder joint, contributing to its stability. The lateral head 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 superior portion of the long head of the triceps is covered by the posterior border of the deltoid muscle. The long head of the triceps can be palpated as an elevation parallel and medial to the posterior border of the deltoid muscle when the elbow is extended.
The triceps brachii can be trained in a variety of ways. It can be worked out in isolation or with compound elbow extension movements. It can also be contracted statically to keep the arm straight against resistance. Isolation movements include cable push-downs, lying triceps extensions, and arm extensions behind the back. Examples of compound elbow extension include pressing movements like the push-up, bench press, and military press.
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Anconeus
The anconeus is a small, triangular muscle located at the elbow, attaching the humerus and ulna. It is part of the superficial extensor compartment, along with the brachioradialis, extensor carpi radialis longus, extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, and extensor carpi ulnaris muscles.
The anconeus muscle assists in the extension of the forearm and provides support for both the dorsal capsule of the humeroulnar joint and the ulna itself. It originates at the dorsal side of the lateral epicondyle of the humerus and inserts at the olecranon of the ulna, along the proximal third of the posterior face of the ulna. The anconeus is supplied by a motor branch of the radial nerve (C6-C8), which arises at the radial sulcus of the humerus.
Functionally, the anconeus constitutes a continuation of the triceps. They are innervated by the same nerve, and their fibres are often either partly or completely blended together. The anconeus is supplied by the posterior interosseous recurrent artery. Its contraction leads to the extension of the forearm at the elbow. It also keeps the tension of the dorsal joint capsule, thus preventing damage during hyperextension.
The anconeus muscle can be easily palpated just lateral to the olecranon process of the ulna. Trauma to the nerve supply of the anconeus muscle can usually result from a shoulder dislocation or fractures of the upper part of the humerus or around the olecranon, or any injury that damages the radial nerve. Any disease that compromises muscular functions, particularly arm extension (e.g. muscular dystrophy), will affect this particular accessory muscle.
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Extensor Carpi Ulnaris
The extensor carpi ulnaris (ECU) is a skeletal muscle located on the ulnar side of the forearm. It is responsible for extending and adducting the wrist, and plays a crucial role in various activities involving these movements. The ECU is particularly important for athletes who engage in forceful wrist movements, such as gripping, throwing, or racket sports.
The ECU is part of the superficial forearm extensor group, which includes muscles such as the anconeus, brachioradialis, extensor carpi radialis longus, extensor carpi radialis brevis, extensor digitorum, and extensor digiti minimi. It originates from the lateral epicondyle of the humerus and the posterior border of the ulna. From there, it crosses the forearm to the ulnar (medial) side and inserts at the base of the fifth metacarpal.
The ECU is innervated by the posterior interosseous nerve (C7 and C8), which is a continuation of the deep branch of the radial nerve. The radial nerve itself stems from the posterior cord of the brachial plexus. Blood supply to the ECU is provided by branches of the radial recurrent and posterior interosseous arteries, which are branches of the radial and ulnar arteries, respectively.
The oblique course of the ECU means that its contraction results in a combined extension and adduction (ulnar deviation) of the hand. This is important for activities such as clenching a fist or making a power grip. Additionally, the ECU works together with other muscles, such as the extensor carpi radialis brevis and extensor carpi radialis longus, to contribute to a balanced extension of the wrist without deviating the hand in the transverse plane.
Injuries to the ECU are common, especially in individuals who participate in activities requiring repetitive arm, elbow, and wrist movements, such as tennis or golf. Symptoms of an ECU injury include pain when shaking hands or squeezing/gripping an object, with the pain intensifying during forceful wrist movements. Treatment options for ECU injuries may include occupational therapy, physical therapy, anti-inflammatory medication, and rest from the aggravating activity.
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Extensor Carpi Radialis Longus
The extensor carpi radialis longus is a muscle that can be found in the posterior compartment of the forearm. It is one of the five main muscles that control movements at the wrist. It is quite long, starting on the lateral side of the humerus and attaching to the base of the second metacarpal bone (metacarpal of the index finger).
The extensor carpi radialis longus is a wrist extensor and can be palpated infero-posteriorly to the elbow. It is a fusiform muscle that forms a flattened tendon that runs distally over the lateral surface of the radius. In the lower third of the forearm, the tendon is crossed by the tendons of the abductor pollicis brevis and extensor pollicis brevis. The tendons of the extensor carpi radialis longus and brevis pass deep to the extensor retinaculum in a common synovial sheath.
The majority of the extensor carpi radialis longus originates from the lateral supracondylar ridge of the humerus (distal third) and the anterior aspect of the lateral intermuscular septum of the arm. A small portion of its fibres originate from the common extensor tendon attached to the lateral epicondyle of the humerus. The fibres unite into a muscle belly, which extends to the middle of the forearm. The muscle belly is then replaced by a flat tendon that travels distally along the lateral surface of the radius, together with the tendon of the extensor carpi radialis brevis.
The extensor carpi radialis longus is one of three primary wrist extensors. It is most effective as a wrist extensor when the elbow is extended and when radial deviation is balanced by the primary ulnar deviator- extensor carpi ulnaris. Functionally, the wrist extensors work strongly in the action of gripping, together with the extensor carpi ulnaris. By keeping the wrist in extension, flexion of the wrist by flexors digitorum superficialis and profundus is prevented, with the result that these muscles act on the fingers. When the wrist then moves into flexion, the flexor tendons are unable to shorten enough to generate effective movement at the interphalangeal joints, resulting in a state of active insufficiency.
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Extensor Digitorum
The extensor digitorum muscle is a long muscle located in the posterior compartment of the forearm. It is a superficial muscle, and the most superficial muscle of the posterior forearm. It is also known as extensor digitorum communis. It extends the medial four digits of the hand, or four medial fingers in their metacarpophalangeal and proximal and distal interphalangeal joints.
The extensor digitorum muscle arises from the lateral epicondyle of the humerus, by the common tendon; from the intermuscular septa between it and the adjacent muscles, and from the antebrachial fascia. It divides below into four tendons, which pass, together with that of the extensor indicis proprius, through a separate compartment of the dorsal carpal ligament, within a mucous sheath.
The tendons then diverge on the back of the hand, and are inserted into the middle and distal phalanges of the fingers. Opposite the metacarpophalangeal articulation, each tendon is bound by fasciculi to the collateral ligaments and serves as the dorsal ligament of this joint. The extensor digitorum muscle is innervated by the posterior interosseous nerve, which is a branch of the radial nerve.
The extensor digitorum muscle is involved in the anatomy of grip, as it contributes to the opening of the hand and letting go of an object. It also extends the wrist and elbow.
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Frequently asked questions
The triceps brachii and anconeus are forearm extensors.
The triceps brachii is a three-headed muscle located at the back of the upper arm. It extends the forearm at the elbow joint and the arm at the shoulder joint.
The anconeus is a small triangular muscle at the elbow joint that extends the forearm. It is located in the superficial region of the posterior forearm compartment.
The extensor muscles in the forearm help to extend the wrist and straighten the fingers.
Some examples of extensor muscles in the forearm include the extensor carpi radialis longus, extensor carpi ulnaris, extensor digitorum, and extensor digiti minimi.
