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The forearm is the part of the upper limb between the elbow and the wrist, and it contains twenty muscles that enable complex movements of the arm, wrist, and fingers. These muscles are divided into two compartments: the anterior (flexor) and the posterior (extensor). The anterior compartment is further divided into three layers: 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 has two origins: the humeral head, which originates from the medial epicondyle of the humerus, and the ulnar head, which originates from the olecranon of the ulna. The muscle tendon passes into the wrist and attaches to the pisiform bone, hook of hamate, and base of the fifth metacarpal. The brachioradialis muscle is part of the posterior compartment of the forearm and allows for the bending of the elbow.
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What You'll Learn
The two types of forearm muscle
The forearm is the section of the upper limb between the elbow and the wrist. There are over twenty muscles in the forearm, which are essential for fine motor actions of the upper limb, allowing for complex movements of the arm, wrist, and fingers. The forearm muscles are divided into two compartments: the anterior (flexor) and the posterior (extensor).
Anterior Forearm Compartment
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. They all originate from a common tendon, which arises from the medial epicondyle of the humerus. The flexor carpi ulnaris has two origins: the humeral head, which originates from the medial epicondyle of the humerus, and the ulnar head, which originates from the olecranon of the ulna. The muscle tendon passes into the wrist and attaches to the pisiform bone, hook of hamate, and base of the fifth metacarpal. The flexor carpi ulnaris is also responsible for moving the wrist back and forth. The other superficial muscles in the anterior forearm have similar attachments, origins, and actions.
The flexor digitorum superficialis is the only muscle in the intermediate layer. There are three muscles in the deep anterior forearm: flexor digitorum profundus, flexor pollicis longus, and pronator quadratus. They originate from the ulna and associated interosseous membrane. The pronator quadratus is a square-shaped muscle that allows you to turn your forearm downward.
Posterior Forearm Compartment
The muscles in the posterior compartment of the forearm are the extensors, which are responsible for the extension of the hand and supination of the forearm. The muscles in the posterior compartment are grouped as follows:
- Superficial layer: Brachioradialis, extensor carpi radialis longus, extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, extensor carpi ulnaris, and anconeus.
- Deep layer: Unknown.
The brachioradialis muscle is the most superficial muscle of the radial side of the forearm, forming the lateral wall of the cubital fossa. It allows you to bend your elbow and turn your arm. The extensor carpi radialis longus and extensor carpi radialis brevis extend the wrist and move the hand away from the direction of the thumb. The extensor digitorum splits into four tendons and connects to the finger joints, helping to straighten or extend the fingers. The extensor digiti minimi extends the little finger. The extensor carpi ulnaris helps to turn and extend the wrist. The anconeus, near the top of the superficial layer, helps extend the forearm at the elbow.
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The role of the ulna and radius
The ulna and radius are the two long bones that make up the forearm, extending from the elbow to the wrist. The radius is the lateral bone of the forearm, located on the thumb side, while the ulna is the medial bone, located on the same side as the pinky finger. The radius is shorter than the ulna and has a small proximal end that articulates with the humerus, and a broad distal end that articulates with the carpal bones at the wrist. The ulna, on the other hand, has a large proximal end that articulates with the humerus and a small distal end. The ulna is slightly longer than the radius.
The design of the radius and ulna, as well as the joints between them, enable pronation and supination of the forearm and hand. The radius and ulna work together to support the forearm and wrist, allowing the wrist and hand to rotate smoothly. The ulna helps the arm, hand, and wrist move smoothly. It also serves as the origin and/or insertion site for more than a dozen muscles and is involved in motions assisted by the elbow and wrist joints.
The radial artery and the ulnar artery provide the blood supply for the entire forearm and hand. The radial artery gives off the recurrent radial branch, which provides blood to the supinator and the brachioradialis muscle. The ulnar artery gives off two recurrent branches, the anterior and posterior, which provide blood to the pronator teres, brachialis, and the proximal portions of the flexor muscles, bones, and elbow joint.
The median, ulnar, and radial nerves run in close proximity to the ulna in the forearm. The median nerve innervates the muscles responsible for flexion of the wrist and the fingers. The ulnar nerve is involved in flexion of the wrist and fingers, as well as spanning the fingers. The radial nerve is the sole nerve involved in the muscles responsible for extension of the forearm, wrist, and fingers.
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Forearm muscle compartments
The forearm is the section of the upper limb from the elbow to the wrist, with its bony structure formed by the radius and ulna. The forearm muscles are divided into two compartments: the anterior (flexor) and posterior (extensor) compartments. These compartments contain twenty muscles that act on the elbow and wrist joints, as well as carpometacarpal, metacarpophalangeal, and interphalangeal joints of the hand. The forearm muscles are essential to the fine motor actions of the upper limb, allowing for complex movements of the arm, wrist, and fingers.
The anterior flexor compartment contains muscles that are largely involved with flexion and supination. The superficial muscles in the anterior compartment are the flexor carpi ulnaris, palmaris longus, flexor carpi radialis, and
The posterior extensor compartment contains muscles that are involved with extension of the hand and supination of the forearm. The muscles in the superficial layer of the posterior compartment include the brachioradialis, extensor carpi radialis longus, extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, extensor carpi ulnaris, and anconeus. The brachioradialis is the most superficial muscle of the radial side of the forearm, forming the lateral wall of the cubital fossa. The anconeus muscle is small and triangular in shape, sometimes blending with triceps brachii or extensor carpi ulnaris. It arises from the humerus to insert on the olecranon of the ulna.
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Flexors and extensors
The forearm is the section of the upper limb from the elbow to the wrist, with a bony structure formed by the radius and ulna. The forearm muscles are divided into two compartments: the anterior (flexor) and the posterior (extensor). These compartments contain twenty muscles that act on the elbow and wrist joints, as well as carpometacarpal, metacarpophalangeal, and interphalangeal joints of the hand.
The flexors of the forearm are located in the anterior compartment and are responsible for flexion of the hand and pronation of the forearm. The superficial muscles in the anterior compartment are the flexor carpi ulnaris, palmaris longus, flexor carpi radialis, and pronator teres. The flexor carpi ulnaris has two origins: the humeral head, which originates from the medial epicondyle of the humerus, and the ulnar head, which originates from the olecranon of the ulna. The muscle tendon passes into the wrist and attaches to the pisiform bone, hook of hamate, and base of the fifth metacarpal. The deep layer of the anterior compartment includes the pronator quadratus, flexor digitorum superficialis, flexor digitorum profundus, and flexor pollicis longus. The flexor digitorum superficialis is the only muscle of the intermediate compartment. It can sometimes be classed as a superficial muscle, but in most individuals, it lies between the deep and superficial muscle layers. The flexor digitorum profundus originates on the proximal three-fourths of the ulna and from the interosseous membrane. Its tendons pass through the carpal tunnel to insert into the bases of their respective distal phalanges, passing between the divided distal superficial flexor tendons.
The extensors of the forearm reside in the posterior compartment and are responsible for the extension of the hand and supination of the forearm. The superficial layer of the posterior compartment includes the brachioradialis, extensor carpi radialis longus, extensor carpi radialis brevis, extensor digitorum, extensor digiti minimi, extensor carpi ulnaris, and anconeus. The extensor carpi ulnaris originates from the humerus and ulna, courses over the ulna, and inserts into the hand. The extensor digitorum originates from the elbow and has four tendons that insert into the fingers, causing extension.
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Blood supply to the forearm
The blood supply to the forearm is a complex process involving multiple arteries, veins, and nerves. The forearm is the region of the upper limb between the elbow and the wrist, containing two long bones, the radius and the ulna, and many muscles, including flexors and extensors of the wrist and digits.
The brachial artery is a major blood supply vessel that continues down the arm from the axillary artery, which in turn continues from the subclavian artery. The subclavian artery is the large vessel that begins the blood supply to the upper extremity, arising near the heart and travelling under the clavicle towards the shoulder. The brachial artery has four branches: the profunda brachii artery, nutrient artery to the humerus, superior ulnar collateral artery, and inferior ulnar collateral artery.
The radial artery and ulnar artery are the two major blood vessels that supply blood to the forearm and are the terminal branches of the brachial artery, arising in the cubital fossa. The radial artery is the smaller of the two branches and supplies blood to the wrist, hand, and elbow joint. It travels deep under the muscle in the forearm until it comes closer to the skin surface near the wrist, where you can feel its pulse. The ulnar artery supplies blood to the medial forearm, including the bones and muscles, and continues into the hand, travelling across the palm as the superficial palmar arch.
The anterior and posterior interosseous arteries supply deeper structures in the forearm, contributing to the blood supply of the radius, ulna, and several muscles. The anterior ulnar recurrent artery, a branch of the ulnar artery, supplies blood to the elbow joint, while the radial recurrent artery, a branch of the radial artery, supplies blood to the brachialis, brachioradialis, and other forearm muscles.
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Frequently asked questions
There are 20 muscles in the forearm.
The forearm is divided into anterior (front) and posterior (rear) compartments.
The muscles in the anterior compartment help with flexion of the hand and pronation of the forearm.
