Logan Steele
Extensor muscles are those that produce extension at the wrist and fingers, or at joints in the body. Extension is a movement that increases the angle between two bones or body surfaces at a joint, resulting in straightening. For example, straightening the arm requires extension at the elbow joint. The forearm contains twenty muscles that act on the elbow and wrist joints, and these muscles are divided into two compartments: the anterior flexor compartment and the posterior extensor compartment. The extensor carpi ulnaris muscle, for example, is the most medial muscle in the superficial posterior compartment of the forearm. It originates from the lateral epicondyle of the humerus and allows for adduction and extension at the wrist. The extensor digiti minimi muscle, on the other hand, is responsible for extending the little finger and contributing to wrist extension. While most extensor muscles are posterior, there are some extensor muscles that are not visible as they are situated proximally in the forearm, such as the anconeus.
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What You'll Learn
- Extensor muscles are commonly found in the posterior compartment of the forearm
- Extensor muscles are innervated by the radial nerve
- Extensor muscles are involved in extension at the wrist and fingers
- Extensor muscles are involved in abduction and adduction of the hand
- Extensor muscles can be superficial or deep
Extensor muscles are commonly found in the posterior compartment of the forearm
The muscles in the posterior compartment of the forearm are commonly referred to as the extensor muscles. The function of these muscles is to produce extension at the wrist and fingers. The extensor muscles in the forearm are innervated by the radial nerve. The muscles in this compartment are organised into two layers: deep and superficial. These two layers are separated by a layer of fascia.
The superficial layer of the posterior forearm contains seven muscles. Four of these muscles (extensor carpi radialis brevis, extensor digitorum, extensor carpi ulnaris, and extensor digiti minimi) share a common tendinous origin at the lateral epicondyle. The extensor carpi ulnaris is the most medial muscle in the superficial posterior compartment of the forearm. It originates from the lateral epicondyle of the humerus via the common extensor tendon. The extensor digiti minimi muscle is innervated by the posterior interosseous nerve. The extensor carpi radialis brevis is a fusiform muscle located deep to its long counterpart, the extensor carpi radialis longus muscle.
The extensor carpi radialis muscles are situated on the lateral aspect of the posterior forearm. Due to their position, they are able to produce abduction as well as extension at the wrist. The anconeus is situated medially and proximally in the extensor compartment of the forearm. It is blended with the fibres of the triceps brachii, and the two muscles are often indistinguishable. Some extensor muscles, such as the anconeus, are not visible as they are situated proximally in the forearm.
The deep compartment of the posterior forearm contains five muscles: the supinator, abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, and extensor indicis. With the exception of the supinator, these muscles act on the thumb and the index finger.
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Extensor muscles are innervated by the radial nerve
The extensor muscles are indeed innervated by the radial nerve. The radial nerve is a major peripheral nerve of the upper limb and is a continuation of the posterior cord of the brachial plexus. It lies on the posterior side of the upper arm and winds around the humerus from medial to lateral under the triceps muscle.
The radial nerve has both motor and sensory functions. The motor branches stimulate the extensor muscles in the posterior forearm, allowing for extension at the wrist and finger joints, and supination of the forearm. The sensory branches supply the skin on the anterolateral arm, distal posterior arm, posterior forearm, and posterolateral wrist and hand areas.
The radial nerve has four branches that provide cutaneous innervation to the skin of the upper limb. Three of these branches arise in the upper arm: the lower lateral cutaneous nerve of the arm, the posterior cutaneous nerve of the arm, and the posterior cutaneous nerve of the forearm. The fourth branch, the superficial branch, is a terminal division of the radial nerve and innervates the dorsal surface of the lateral three and a half digits and the dorsum of the hand.
The deep branch of the radial nerve, also known as the posterior interosseous nerve, innervates the remaining muscles of the posterior forearm. This includes muscles such as the extensor carpi radialis brevis, the extensor digitorum, the extensor carpi ulnaris, and the extensor digiti minimi. These muscles are responsible for movements such as wrist extension, finger extension, and abduction of the hand.
In summary, the extensor muscles are innervated by the radial nerve, which has both motor and sensory functions and plays a crucial role in the movement and sensation of the upper limb, particularly the posterior forearm and hand.
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Extensor muscles are involved in extension at the wrist and fingers
The muscles in the posterior compartment of the forearm are commonly referred to as the extensor muscles. Their primary function is to produce extension at the wrist and fingers. These muscles generally originate on or near the lateral epicondyle and insert on the distal forearm or in the hand. The extensor muscles are all innervated by the radial nerve.
The extensor carpi radialis brevis (ECRB), extensor carpi radialis longus (ECRL), and the extensor carpi ulnaris (ECU) muscles work together to achieve neutral wrist extension movements. The ECRB and ECRL muscles also contribute to the extension and abduction of the hand at the wrist joint. The ECU is the most medial muscle in the superficial posterior compartment of the forearm. It originates from the lateral epicondyle of the humerus and inserts at the base of the fifth metacarpal, contributing to the extension and adduction of the wrist.
The extensor digitorum (ED) is another important muscle for extension at the wrist and fingers. It divides into four tendons, which pass through the dorsal carpal ligament and follow the fingers. The ED is responsible for the extension of the second, third, fourth, and fifth digits. The extensor digiti minimi (EDM) is specifically responsible for extending the fifth digit at its metacarpophalangeal (MCP) joint and contributes to the extension of the hand at the wrist joint.
The thumb has separate extensors, allowing for more independent movement compared to the other fingers. Thumb extension is achieved by the abductor pollicis longus (APL), extensor pollicis brevis (EPB), and extensor pollicis longus (EPL). The EPB and EPL tendons create the medial and lateral borders of the anatomical snuffbox on the dorsal aspect of the wrist. The index finger, or second digit, can also be extended independently by the extensor indicis proprius (EIP) muscle.
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Extensor muscles are involved in abduction and adduction of the hand
Extensor muscles are commonly known as the muscles in the posterior compartment of the forearm. Their general function is to produce extension at the wrist and fingers. Extensor muscles are involved in abduction and adduction of the hand.
The extensor carpi radialis brevis and the extensor carpi radialis longus, for example, work together to extend and abduct the hand at the wrist joint. The extensor carpi ulnaris, on the other hand, is located on the medial side of the posterior forearm, allowing it to produce adduction and extension at the wrist. The extensor digitorum brevis manus (EDBM) is a rare anatomical variant of the extensor compartment of the wrist and hand, and it has been found to cause finger abduction.
The extensor digitorum extends the digits except the thumb and is also involved in wrist extension. The extensor digiti minimi, which is thought to originate from the extensor digitorum, extends the little finger and contributes to wrist extension. The extensor indicis proprius extends the index finger.
The extensor muscles in the posterior forearm are organised into two layers: deep and superficial. These two layers are separated by a layer of fascia. The superficial layer contains seven muscles, four of which extensor carpi radialis brevis, extensor digitorum, extensor carpi ulnaris, and extensor digiti minimi share a common tendinous origin at the lateral epicondyle.
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Extensor muscles can be superficial or deep
The muscles in the posterior compartment of the forearm are commonly referred to as the extensor muscles. These muscles are responsible for producing extension at the wrist and fingers. They are innervated by the radial nerve. The extensor muscles can be organised into two layers: deep and superficial.
The superficial layer of the posterior forearm contains seven muscles. Four of these muscles, namely the extensor carpi radialis brevis, extensor digitorum, extensor carpi ulnaris, and extensor digiti minimi, share a common tendinous origin at the lateral epicondyle. The extensor digiti minimi muscle is thought to originate from the extensor digitorum muscle, and these two muscles are sometimes fused together. The extensor carpi ulnaris is the most medial muscle in the superficial posterior compartment of the forearm. It originates from the lateral epicondyle of the humerus and its prime function is adduction (ulnar deviation) of the hand at the wrist joint. The extensor carpi radialis brevis is a fusiform muscle located deep to its long counterpart, the extensor carpi radialis longus muscle. It arises from the lateral epicondyle of the humerus and shares a common extensor tendon with the extensor digitorum, extensor carpi ulnaris, and extensor digiti minimi muscles.
The deep layer of the posterior forearm contains five muscles: the supinator, abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, and extensor indicis. With the exception of the supinator, these muscles act on the thumb and the index finger. The supinator has two heads of origin: one from the lateral epicondyle of the humerus and the other from the posterior surface of the ulna. It is involved in supinating the forearm. The abductor pollicis longus is situated immediately distal to the supinator muscle.
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Frequently asked questions
Extensor muscles are muscles that produce extension at the wrist and fingers. They are commonly found in the posterior compartment of the forearm.
No, they are not always posterior. While the extensor muscles in the forearm are located in the posterior compartment, there are also extensor muscles in other parts of the body, such as the back, that are not exclusively posterior.
Some examples of extensor muscles include the extensor carpi radialis brevis, extensor digitorum, extensor carpi ulnaris, and extensor digiti minimi in the forearm. In the back, the transversospinalis muscle group assists in posterior bending of the back.
