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The supinator muscle is a broad muscle in the posterior compartment of the forearm, responsible for supinating the forearm. It curves around the upper third of the radius and consists of two layers of fibres, between which passes the deep branch of the radial nerve. Supination is a unique movement only possible in the forearms and hands, allowing the human body to flip the palm either face up or face down. The supinator muscle works with the biceps brachii to supinate the forearm by pulling on the radius.
| Characteristics | Values |
|---|---|
| Name | Supinator muscle |
| Location | Posterior compartment of the forearm |
| Shape | Broad/long, flat, fusiform |
| Consistency | Two layers of fibres/planes of fibres |
| Nerve | Radial nerve, deep branch |
| Function | Supinate the forearm |
| Synergistic Muscles | Biceps Brachii |
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What You'll Learn
- The supinator muscle is located in the posterior compartment of the forearm
- It works with the biceps brachii for powerful supination
- The supinator is innervated by the deep branch of the radial nerve
- Supination strength decreases by 64% if the supinator is injured
- The supinator muscle consists of two layers of fibres
The supinator muscle is located in the posterior compartment of the forearm
The two layers of fibres, or planes, are the superficial and the deep plane. The superficial plane originates as tendons and surrounds the upper part of the radius, inserting into the lateral edge of the radial tuberosity and the oblique line of the radius. The deeper plane originates by muscular fibres and forms a sling-like fasciculus, encircling the neck of the radius above the tuberosity and attaching to the back part of its medial surface.
The supinator muscle is innervated by the deep branch of the radial nerve, which becomes the posterior interosseous nerve upon exiting the supinator muscle. The radial nerve divides into deep and sensory superficial branches just proximal to the supinator muscle, which can lead to entrapment and compression of the deep branch, potentially resulting in selective paralysis of the muscles served by this nerve.
The supinator muscle is the prime supinator of the forearm, working with the biceps brachii to supinate the forearm by pulling on the radius. The supinator is the most active muscle in forearm supination during unresisted supination, while the biceps become increasingly active with heavy loading.
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It works with the biceps brachii for powerful supination
The supinator muscle is the prime muscle responsible for supinating the forearm. It is a broad muscle located in the posterior compartment of the forearm, curved around the upper third of the radius. The supinator muscle consists of two layers of fibres, with the deep branch of the radial nerve passing between them.
The biceps brachii also plays a role in supinating the forearm. It acts primarily as an elbow flexor and secondarily as a supinator. The biceps brachii is able to supinate the forearm when the elbow is flexed. However, when the elbow is fully extended, the supinator muscle takes over this action.
The supinator muscle and the biceps brachii work together to produce powerful supination. The supinator muscle is always active during forearm supination, but the biceps brachii becomes increasingly active when there is heavy loading. Supination strength decreases significantly if the supinator is disabled, such as by injury.
During supination, these muscles pull on the radius, rotating it in the opposite direction of the pronator muscles. This movement turns the hand, wrist, and forearm, allowing the palm to face anteriorly or superiorly.
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The supinator is innervated by the deep branch of the radial nerve
The supinator muscle is a broad muscle located in the posterior compartment of the forearm. It is responsible for supinating the forearm, allowing the hand to be brought into the supinated position. This muscle works in conjunction with the biceps, except when the elbow joint is extended. The supinator muscle has a unique structure, consisting of two layers or planes of fibres that originate from the ulna and humerus.
The supinator muscle is innervated by the deep branch of the radial nerve. This nerve is a peripheral nerve that supplies specific parts of the arm, forearm, wrist, and hand. It has both motor and sensory functions, activating the muscles responsible for movements and providing sensation to the surrounding areas. The radial nerve divides into deep and sensory superficial branches just proximal to the supinator muscle, with the deep branch passing through the muscle in most cases.
The deep branch of the radial nerve plays a crucial role in the function of the supinator muscle. It passes between the two heads or layers of the supinator, providing the necessary stimulation for muscle contraction. This nerve then becomes the posterior interosseous nerve upon exiting the supinator muscle. The posterior interosseous nerve continues to innervate the posterior compartment muscles of the forearm, ensuring their proper function.
The innervation of the supinator muscle by the deep branch of the radial nerve is of clinical significance. The arrangement of the nerve passing just proximal to the muscle can lead to a condition known as supinator entrapment syndrome. This syndrome occurs when there is entrapment and compression of the deep branch of the nerve, potentially resulting in selective paralysis of the muscles it supplies, including the extensor muscles and the abductor pollicis longus.
Understanding the relationship between the supinator muscle and the deep branch of the radial nerve is essential for both anatomical and clinical reasons. The innervation provided by this nerve allows the supinator muscle to perform its function of supinating the forearm. However, the proximity of the nerve to the muscle also creates a vulnerability to nerve entrapment and potential neurological complications. Therefore, the deep branch of the radial nerve is crucial for the normal function of the supinator muscle and overall movement of the forearm.
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Supination strength decreases by 64% if the supinator is injured
The supinator muscle is a broad muscle in the posterior compartment of the forearm. It is the prime mover of the forearm and is responsible for supination. The supinator works in conjunction with the biceps muscle to perform this function. However, the supinator is the most active muscle during forearm supination when there is no resistance. The biceps become more active during heavy loading.
Supination is the action of turning the hand so that the palm faces upward or forward. It is the opposite of pronation, which is the action of turning the hand so that the palm faces downward or backward. The ability to supinate and pronate gives the upper limb enhanced functionality and a mechanical advantage.
The supinator muscle is innervated by the deep branch of the radial nerve, which becomes the posterior interosseous nerve upon exiting the supinator muscle. The radial nerve divides into deep and superficial branches just proximal to the supinator muscle. This arrangement can lead to entrapment and compression of the deep branch, potentially resulting in selective paralysis of the muscles served by this nerve.
If the supinator is injured or disabled, supination strength decreases by 64%. This significant decrease in strength highlights the crucial role of the supinator muscle in forearm supination. The injury to the supinator can be caused by various factors, including compression by soft tissue masses surrounding the nerve and stress from repetitive supination and pronation movements.
It is important to note that the supinator muscle is not the only muscle involved in supination. Other muscles, such as the biceps brachii and brachioradialis, also play a role in this movement. However, the supinator is the primary muscle responsible for supination, and its injury can lead to a substantial decrease in supination strength.
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The supinator muscle consists of two layers of fibres
The supinator muscle is a broad muscle located in the posterior compartment of the forearm. It is responsible for supinating the forearm, which involves rotating the forearm so that the palm faces anteriorly or superiorly. This movement is essential for various functional tasks, such as turning a screwdriver or holding a bowl of soup.
The deeper layer of fibres, or the deeper plane, originates from the same structures as the superficial layer but consists of muscular fibres. It forms a sling-like structure, encircling the neck of the radius above the radial tuberosity. This deeper layer attaches to the back part of the medial surface of the radius.
The radial nerve, which innervates the supinator muscle, passes between these two layers. Specifically, the deep branch of the radial nerve travels through the belly of the supinator in most cases. This arrangement of the radial nerve within the supinator muscle can make it susceptible to entrapment and compression, potentially leading to selective paralysis of the muscles it serves.
The supinator muscle works in conjunction with the biceps brachii to achieve forearm supination. While the biceps brachii play a more significant role in supination when the elbow is flexed, the supinator muscle becomes the primary supinator when the elbow is fully extended. Together, these muscles pull on the radius to produce the supination movement.
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Frequently asked questions
The supinator muscle is a broad muscle in the posterior compartment of the forearm. It curves around the upper third of the radius and consists of two layers of fibres.
The supinator muscle supinates the forearm. This means it rotates the forearm so that the palm faces upwards.
The supinator muscle always works together with the biceps brachii. The biceps brachii is unable to supinate when the elbow is extended, so in this case, the supinator acts alone.
