Logan Steele
The forearm is the region of the upper limb between the elbow and the wrist. It contains two long bones, the radius and the ulna, which form the two radioulnar joints. The forearm contains many muscles, including flexors and extensors of the wrist and digits, a flexor of the elbow, and pronators and supinators. These muscles are divided into two compartments: the anterior (flexor) and posterior (extensor) compartments, each with superficial and deep layers. The forearm muscles are essential for fine motor actions, allowing complex movements of the arm, wrist, and fingers.
| Characteristics | Values |
|---|---|
| Number of muscles | 20 |
| Number of bones | 2 |
| Names of the bones | Radius and Ulna |
| Function of muscles | Flexion, pronation, supination, extension |
| Flexors | Anterior muscles |
| Extensors | Posterior muscles |
| Blood supply | Anterior ulnar recurrent artery, posterior ulnar recurrent artery, ulnar artery, brachial artery, radial artery |
| Nerve supply | Median nerve, ulnar nerve, Radial nerve, anterior interosseous nerve, posterior interosseous nerve |
| Superficial muscles | Pronator Teres, Flexor Carpi Radialis, Palmaris Longus, Flexor Carpi Ulnaris |
| Deep muscles | Flexor digitorum profundus, flexor pollicis longus, pronator quadratus |
| Intermediate muscles | Flexor digitorum superficialis |
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What You'll Learn
The forearm has two muscular compartments
The forearm is the region of the upper limb between the elbow and the wrist. It contains two long bones, the radius and the ulna, which form the two radioulnar joints. The forearm contains many muscles, including flexors and extensors of the wrist and digits, a flexor of the elbow, and pronators and supinators that turn the hand.
The anterior compartment contains the flexor muscles, which are supplied mainly by the median nerve. The flexor muscles include the flexor carpi radialis, flexor carpi ulnaris, palmaris longus, and flexor digitorum superficialis. The flexor carpi radialis and flexor carpi ulnaris stretch from the humerus (upper-arm bone) to the metacarpal bones of the hand and flex the wrist. The palmaris longus helps flex the wrist, and the flexor digitorum superficialis is the only muscle in the intermediate layer, helping to bend the fingers and move the wrist.
The posterior compartment contains the extensor muscles, which are supplied by the radial nerve. The extensor muscles include the extensor carpi radialis longus, radialis brevis, ulnaris, and digitorum. The extensor carpi radialis longus, radialis brevis, and ulnaris attach to the proximal portion of the second, third, and fifth metacarpals, respectively. The extensor digitorum divides into three slips, attaching to the middle and distal phalanx of each of the digits.
The flexor muscles are generally larger than the extensor muscles because they work against gravity and act as anti-gravity muscles.
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The anterior and posterior compartments contain 20 muscles
The forearm is the region of the upper limb between the elbow and the wrist. The forearm contains two long bones, the radius and the ulna, forming two radioulnar joints. The forearm contains many muscles, including flexors and extensors of the wrist and digits, a flexor of the elbow (brachioradialis), and pronators and supinators.
The forearm can be divided into two fascial compartments: the anterior (flexor) and posterior (extensor) compartments. Together, these compartments contain 20 muscles that act on the elbow and wrist joints, as well as the carpometacarpal, metacarpophalangeal, and interphalangeal joints of the hand. The forearm muscles facilitate complex movements of the arm, wrist, and fingers.
The anterior compartment contains the flexors and is primarily supplied by the median nerve. The flexor muscles are larger than the extensors as they work against gravity. The superficial muscles in the anterior compartment include the flexor carpi ulnaris, palmaris longus, flexor carpi radialis, and pronator teres. The flexor digitorum superficialis is the only muscle of the intermediate compartment. It can be classified as a superficial muscle, but it typically lies between the deep and superficial muscle layers. The deep anterior forearm contains three muscles: flexor digitorum profundus, flexor pollicis longus, and pronator quadratus.
The posterior compartment contains the extensors of the hands, which are supplied by the radial nerve. The extensor carpi radialis longus, radialis brevis, and ulnaris attach to the proximal portion of the second, third, and fifth metacarpals, respectively. The extensor digitorum runs under the extensor retinaculum and divides to attach to the middle and distal phalanx of each of the second to fifth digits. The anconeus is considered part of the posterior compartment by some.
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The flexor carpi radialis and flexor carpi ulnaris
The forearm is the region of the upper limb between the elbow and the wrist, containing two long bones, the radius and ulna, which form the two radioulnar joints. The forearm contains many muscles, including flexors and extensors of the wrist, flexors and extensors of the digits, and pronators and supinators.
The flexor carpi ulnaris has two heads, one arising from the medial epicondyle of the humerus, and the other from the olecranon and proximal three-fourths of the ulna's subcutaneous margin. These two heads are connected by a tendinous arch. The muscle inserts on the bases of the second, third, and fifth metacarpals. The flexor carpi ulnaris is supplied by the ulnar collateral arteries, along with the anterior and posterior ulnar recurrent arteries.
The flexor carpi radialis is also involved in flexing the hand at the wrist, contracting with the flexor carpi ulnaris and palmaris longus. It is innervated by the median nerve.
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The flexor digitorum superficialis and profundus
The forearm is the region of the upper limb between the elbow and the wrist. It contains many muscles, including flexors and extensors of the wrist and digits. The forearm muscles are divided into two compartments: the anterior (flexor) and the posterior (extensor).
The flexor digitorum superficialis is the only muscle of the intermediate compartment. It is sometimes classified as a superficial muscle, but in most cases, it lies between the deep and superficial muscle layers. It is a good anatomical landmark in the forearm, as the median nerve and ulnar artery pass between its two heads. The muscle has two heads: one that originates from the medial epicondyle of the humerus and the other from the radius. The muscle splits into four tendons at the wrist, which travel through the carpal tunnel and attach to the base of the middle phalanx of the four digits. The flexor digitorum superficialis flexes the metacarpophalangeal joints and proximal interphalangeal joints at the four fingers, and flexes at the wrist.
The flexor digitorum superficialis is the largest muscle of the anterior compartment of the forearm. It is part of the superficial flexors of the forearm, along with the pronator teres, flexor carpi radialis, flexor carpi ulnaris, and palmaris longus. However, some sources classify this muscle as an independent middle/intermediate layer of the anterior forearm, found between the superficial and deep groups.
The flexor digitorum profundus is one of three muscles in the deep anterior forearm, along with the flexor pollicis longus and pronator quadratus. It originates from the ulna and associated interosseous membrane. At the wrist, it splits into four tendons, which pass through the carpal tunnel and attach to the distal phalanges of the four fingers. The flexor digitorum profundus is the only muscle that can flex the distal interphalangeal joints of the fingers. It also flexes the metacarpophalangeal joints and the wrist.
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The pronator teres and brachialis
The forearm is the region of the upper limb between the elbow and the wrist. It contains two long bones, the radius and ulna, and many muscles, including flexors, extensors, and pronators. The pronator teres and brachialis are two muscles that play important roles in the function and movement of the forearm.
The pronator teres is a long, round muscle located primarily in the forearm. It has two heads, the humeral head and the ulnar head, which originate from different parts of the humerus and ulna, respectively. The humeral head is larger and more superficial, while the ulnar head is deeper and joins the humeral head at an acute angle. The pronator teres muscle fibres insert near the middle of the radius. This muscle is responsible for pronating the forearm, or turning it so that the palm faces downwards. It works together with the pronator quadratus to pull the radius medially, causing the radial head to rotate around the proximal ulna. This action is essential for various sporting activities and fine motor movements of the upper limb.
The blood supply to the pronator teres comes from branches of the brachial, radial, and ulnar arteries, including the common interosseus artery and the anterior ulnar recurrent artery. The median nerve innervates the pronator teres, entering the forearm between its two heads. Pronator teres syndrome can occur when this nerve is compressed, leading to pain, numbness, and possible motor dysfunction.
The brachialis muscle, on the other hand, is a powerful elbow flexor that acts synergistically with the biceps brachii to flex the elbow. It originates from the distal anterior humerus and inserts onto the coronoid process of the ulna. The brachialis muscle is innervated by the musculocutaneous nerve, which arises from the lateral cord of the brachial plexus. This nerve provides motor control for the contraction of the brachialis, enabling the elbow flexion movement.
The brachialis muscle is an important stabiliser of the elbow joint and assists in holding heavy weights. It is thicker and stronger than the biceps brachii, reflecting its crucial role in supporting the elbow. The blood supply to the brachialis comes from the brachial artery, which is a direct continuation of the axillary artery as it enters the cubital fossa.
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Frequently asked questions
The forearm is the region of the upper limb between the elbow and the wrist. It contains two long bones, the radius and the ulna, forming the two radioulnar joints. The forearm contains many muscles, including flexors and extensors of the wrist and digits, and pronators and supinators that turn the hand.
The forearm contains around twenty muscles, divided between the anterior (flexor) and posterior (extensor) compartments. The superficial part of the flexor surface contains five muscles, while the deep anterior forearm contains three muscles: flexor digitorum profundus, flexor pollicis longus, and pronator quadratus.
The forearm muscles are essential for fine motor actions, allowing for complex movements of the arm, wrist, and fingers. For example, the pronator teres muscle rotates the forearm, the flexor carpi radialis helps move the arm away from the body, and the palmaris longus flexes the wrist.
