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Extensor muscles are muscles that increase the angle between members of a limb, resulting in straightening. They are the opposite of flexor muscles, which help in bending our elbows, knees and fingers. Extensor muscles arise from extensor muscle bellies, which coordinate extension of the wrist and fingers. Extensor muscles of the thumb and fingers include the extensor policis brevis, abductor pollicis longus, extensor pollicis longus, extensor digitorum communis, and extensor indicis proprius. Extensors in the foot include the extensor digitorum longus and extensor digitorum brevis, which act on the toes.
| Characteristics | Values |
|---|---|
| Definition | Any of the muscles that increase the angle between members of a limb |
| Movement | Usually directed backward, with the exception of the knee joint |
| Function | Help in straightening or extending |
| Body parts | Elbow, knee, wrist, spine, fingers, thumb, neck |
| Example | Extensor carpi radialis brevis, extensor carpi radialis longus, extensor carpi ulnaris, extensor digitorum, extensor indicis, extensor pollicis brevis, extensor pollicis longus, extensor digitorum longus, extensor digitorum brevis, extensor medii proprius, extensor digiti minimi |
| Innervation | Branches of the radial nerve (C6–C8) |
| Layers | Superficial and deep |
| Origin | Ulna and radius in their mid portion |
| Example of superficial muscles | Extensors of the wrist |
| Example of deep muscles | Extensor muscles of the thumb and fingers |
| Juncturae | Type 1, filamentous band; type 2, fibrous band; and type 3, tendinous band |
| Function of juncturae | Stabilization of the metacarpophalangeal joints, force distribution during finger extension, and coordination of tendon movements |
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What You'll Learn
Extensors increase the angle between bones
Extensor muscles are those that increase the angle between bones or body surfaces at a joint, usually resulting in the straightening of the bones or body surfaces involved. For example, the extension of a flexed (bent) elbow or the straightening of the wrist or spine backward.
In the hand, extensor muscles include the extensor carpi radialis brevis, extensor carpi radialis longus, and extensor carpi ulnaris, which run from the humerus (upper arm bone) along the back of the forearm to the metacarpal bones at the back of the hand, extending the wrist. The extensor digitorum runs from the humerus to a common tendon attached to all fingers and extends them. The extensor indicis acts upon the index finger, while the extensor pollicis brevis and extensor pollicis longus run from the radius and ulna (bones of the forearm) and act upon the thumb. The extensor digitorum communis (EDC) muscles are responsible for the extension of the index, long, ring, and small fingers.
Extensor muscles of the thumb and fingers arise from two main anatomic origins: a superficial and a deep layer. The deep layer of muscles includes the extensor muscles of the thumb and fingers: extensor policis brevis (EPB), abductor pollicis longus (APL), extensor pollicis longus (EPL), extensor digitorum communis (EDC), and extensor indicis proprius (EIP). The more superficial muscles consist of the extensors of the wrist: extensor carpi radialis longus (ECRL), extensor carpi radialis brevis (ECRB), extensor digiti minimi (EDM), and extensor carpi ulnaris (ECU).
The extensor tendons enter the dorsum of the hand through six extensor tendon compartments covered by the extensor retinaculum, which prevents tendon bowstringing, allowing efficient extension. The intertendinous connections between the extensor tendons of the fingers provide stabilization of the metacarpophalangeal joints, force distribution during finger extension, and coordination of tendon movements.
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They help straighten the elbow, knee, wrist or spine
Extensor muscles help to straighten the elbow, knee, wrist, or spine. They increase the angle between the bones of a limb, which results in straightening. For example, extension occurs when a bent elbow is straightened.
In the hand, extensor muscles include the extensor carpi radialis brevis, extensor carpi radialis longus, and extensor carpi ulnaris, which extend the wrist. The extensor digitorum extends the fingers, and the extensor indicis acts upon the index finger. The thumb is acted upon by the extensor pollicis brevis and extensor pollicis longus. Extensor muscles of the thumb and fingers include the extensor policis brevis (EPB), abductor pollicis longus (APL), extensor pollicis longus (EPL), extensor digitorum communis (EDC), and extensor indicis proprius (EIP). The EPB and APL are also involved in wrist extension.
The extensor digitorum communis (EDC) muscles are responsible for the extension of the index, long, ring, and small fingers. The extensor digitorum is connected by juncturae tendinae, or connective tissues, at the base of the MCP joints. The EDC tendon pulls on the sagittal bands, extending the metacarpophalangeal joint.
Extensors in the foot include the extensor digitorum longus and extensor digitorum brevis, which act upon the toes. The extensor digitorum longus and brevis originate in the upper and lower parts of the lower leg, respectively.
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Extensors are innervated by branches of the radial nerve
Extensor muscles are those that increase the angle between members of a limb, such as by straightening the elbow or knee or bending the wrist or spine backward. Extensors in the foot include the extensor digitorum longus and extensor digitorum brevis, which act on the toes. Extensors in the hand include the extensor carpi radialis brevis, extensor carpi radialis longus, and extensor carpi ulnaris, which extend the wrist.
The radial nerve is a peripheral nerve that supplies specific parts of the arm, forearm, wrist, and hand. It has both motor and sensory functions. The motor branches stimulate the posterior arm muscles, posterior forearm muscles, and extrinsic wrist and hand extensors. The sensory branches supply the skin on the anterolateral arm, distal posterior arm, posterior forearm, and posterolateral wrist and hand areas.
The radial nerve divides into a superficial branch (primarily sensory) and a deep branch (primarily motor). The deep branch of the radial nerve, also known as the posterior interosseous nerve, pierces the supinator muscle, winds around the radius, and reaches the posterior of the forearm. It then pierces the supinator again and passes deep through the extensor pollicis brevis to the extensor pollicis longus. It continues along with the posterior interosseous artery and ends as a pseudoganglion below the extensor retinaculum, supplying the wrist and intercarpal joints.
The radial nerve provides motor innervation to the muscles in the posterior compartment of the arm and forearm, which are mostly extensors. The deep branch of the radial nerve is entirely motor and innervates the extrinsic extensors of the wrists and hands. The extensors are innervated by branches of the radial nerve, specifically the deep branch of the radial nerve.
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Extensor muscles have superficial and deep layers
Extensor muscles are responsible for increasing the angle between members of a limb, resulting in straightening or extension. For example, extension occurs when a flexed elbow is straightened. Extensors in the hand include muscles such as the extensor carpi radialis brevis, extensor carpi radialis longus, and extensor carpi ulnaris, which extend the wrist. The extensor digitorum extends the fingers, the extensor indicis acts upon the index finger, and the extensor pollicis brevis and extensor pollicis longus act upon the thumb.
The superficial layer, on the other hand, consists of the extensors of the wrist. These are the extensor carpi radialis longus, extensor carpi radialis brevis, extensor digiti minimi, and extensor carpi ulnaris. The muscles of the superficial layer originate on the lateral epicondyle of the humerus. This group also includes the brachioradialis muscle, which is involved in elbow extension.
The extensor tendons play a crucial role in facilitating the extension of the wrist and fingers. They arise from the corresponding extensor muscle bellies and coordinate the extension movements. The extensor tendons enter the dorsum of the hand through six tendon compartments covered by the extensor retinaculum, which prevents tendon bowstringing and enables efficient extension.
The intertendinous connections between the extensor tendons also contribute to the overall function of the extensor mechanism. These connections provide stabilization to the metacarpophalangeal joints, distribute forces during finger extension, and coordinate tendon movements. The juncturae tendinum interconnect the extensor digitorum tendons, providing stability at the base of the MCP joints.
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Extensor tendons connect to the metacarpophalangeal joints
Extensor muscles are muscles that increase the angle between members of a limb, such as straightening the elbow or knee, or bending the wrist or spine backward. The extensor digitorum muscle, for example, extends the medial four digits of the hand. Extensor muscles arise from extensor muscle bellies, which coordinate extension of the wrist and fingers.
Extensor tendons arise from the corresponding extensor muscle bellies. The extensor tendons of the fingers cross both the metacarpophalangeal (MCP) and interphalangeal joints. The extensor tendons in all fingers have a metachromatic sesamoid fibrocartilage on their deep surface. This fibrocartilage phenotype is marked by chondroitin 6 sulphate and type II collagen. The labelling profile of the tendon fibrocartilage in the different fingers at the MCP joints is similar to that at the PIP joints. The extensor tendons enter the dorsum of the hand via six extensor tendon compartments covered by the extensor retinaculum.
The intertendinous connections of the extensor tendons have three key functions: stabilization of the metacarpophalangeal joints, force distribution during finger extension, and coordination of tendon movements. Juncturae are intertendinous connections that limit extension in certain fingers when others are flexed at the metacarpophalangeal joints.
The extensor tendons of the index and long fingers are connected by junctura A, junctura B connects the long and ring fingers, and junctura C connects the ring and small fingers. The patterns of these intertendinous connections can be classified into three types: filamentous, fibrous, and tendinous bands.
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Frequently asked questions
Extensor muscles are muscles that increase the angle between members of a limb, resulting in straightening.
Examples of extensor muscles include the extensor carpi radialis brevis, extensor carpi radialis longus, and extensor carpi ulnaris, which extend the wrist. The extensor digitorum extends the fingers.
Extensor muscles help in straightening or extending body parts. For example, the extensor carpi radialis brevis, extensor carpi radialis longus, and extensor carpi ulnaris muscles work together to achieve neutral wrist extension movements.
Extensor tendons arise from the corresponding extensor muscle bellies that coordinate extension of the wrist and fingers. The extensor tendons enter the dorsum of the hand through six extensor tendon compartments covered by the extensor retinaculum.
