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The human body is capable of a wide range of movements, including pronation and supination. These movements define the orientation of the palm, forearm, or foot in space. While pronation is the movement of the hand to turn the palm posteriorly or face down, supination is the movement that turns the palm anteriorly or face up. The supinator muscle of the forearm and the biceps brachii of the upper arm are the primary muscles responsible for supination. The supinator muscle is located in the posterior compartment of the forearm, and its function is to supinate the forearm. This muscle works in conjunction with the biceps brachii to achieve powerful supination.
| Characteristics | Values |
|---|---|
| Definition | Supination is the movement of the hand, wrist, and forearm to a position where the palm faces upwards. |
| Muscles Involved | Supinator muscle, Biceps Brachii, Brachialis, Brachioradialis |
| Bones Involved | Radius, Ulna |
| Joints Involved | Radioulnar joints |
| Nerves Involved | Radial nerve, Posterior interosseus nerve |
| Related Actions | Turning a screwdriver, turning a key, looking at palms, holding a bowl of soup |
| Related Conditions | Supinator entrapment syndrome, "Popeye" deformity |
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What You'll Learn
- The supinator muscle is a broad muscle in the forearm
- The biceps brachii is a supinator of the forearm
- The supinator and biceps work together for powerful supination
- The supinator is a location where the radial nerve can be entrapped
- Supination is important for daily activities, like turning a screwdriver
The supinator muscle is a broad muscle in the forearm
The supinator consists of two layers or planes of fibres, with the deep branch of the radial nerve passing between them. The superficial layer of fibres has a tendinous origin, surrounding the upper part of the radius. In contrast, the deeper layer of fibres forms a sling-like structure that encircles the neck of the radius above the radial tuberosity.
The radial nerve, which supplies the supinator muscle, divides into deep and sensory superficial branches just proximal to the muscle. This arrangement can make the radial nerve susceptible to entrapment and compression, potentially resulting in selective paralysis of the muscles it serves. This condition is known as supinator entrapment syndrome and can be caused by repetitive supination and pronation movements.
Supination of the forearm involves twisting the forearm into the palm-up position. The supinator muscle works alongside the biceps brachii to achieve this movement, with the biceps providing approximately half of the power required for supination. However, the biceps brachii is unable to supinate when the elbow is fully extended, whereas the supinator muscle can facilitate supination in all positions of the elbow.
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The biceps brachii is a supinator of the forearm
The biceps brachii is a large muscle that lies on the front of the upper arm between the shoulder and the elbow. It is one of the three muscles in the anterior compartment of the upper arm, along with the brachialis and coracobrachialis muscles. The biceps brachii is also one of the three muscles that flex the elbow, along with the brachialis and brachioradialis.
The biceps brachii is a powerful supinator of the forearm, i.e. it turns the palm upwards. This action requires the elbow to be at least partially flexed. If the elbow is fully extended, supination is carried out by the supinator muscle. The biceps brachii is a particularly powerful supinator due to its distal attachment to the radial tuberosity, on the opposite side of the bone from the supinator muscle. When flexed, the biceps brachii pulls the radius back into its neutral supinated position, working in conjunction with the supinator muscle.
The supinator muscle is located in the posterior compartment of the forearm. It is a broadly shaped muscle that curves around the upper third of the radius and consists of two layers of fibres. The supinator muscle has a broad origin from the ulna and humerus, and the two layers of fibres originate from the supinator crest of the ulna, the lateral epicondyle of the humerus, the radial collateral ligament, and the annular radial ligament.
Supination and pronation are movements that define the orientation of the palm, forearm, or foot in space. They are important movements that help us perform various daily activities. In the upper limb, pronation is the rotatory movement during which the palm and forearm face downward, while supination refers to the movement of the palm facing upwards.
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The supinator and biceps work together for powerful supination
The supinator muscle and the biceps brachii are the primary muscles responsible for supination, a movement unique to the forearms and hands. This movement involves rotating the forearm so that the palm faces upwards, a position often assumed when holding a bowl or looking at the palm.
The supinator muscle is a broad, flat muscle located in the posterior compartment of the forearm. It curves around the upper third of the radius, one of the two bones in the forearm, and consists of two layers of fibres. The deep branch of the radial nerve passes through the supinator muscle, dividing into deep and superficial branches. This arrangement can lead to nerve entrapment and potential paralysis of the muscles served by this nerve.
The biceps, as the name suggests, has two heads: a short head and a long head. The biceps is the main supinator of the forearm and provides about half of the power for supination. It works with the supinator muscle to achieve powerful supination, although it is unable to supinate when the elbow is extended. The biceps also help in bending the elbow, with the supination movement allowing for a stronger bending action.
Supination is an important movement that enables us to perform various daily activities such as turning a screwdriver or a key. However, injury to the upper limb can damage the nerves and muscles involved in supination, potentially leading to a loss of supination strength.
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The supinator is a location where the radial nerve can be entrapped
The supinator muscle is a broad, curved muscle located in the superior and posterior compartment of the forearm. It is responsible for supination of the forearm, which is the movement that turns the palm to face upwards. This muscle works in conjunction with the biceps brachii to achieve powerful supination, although the bicep is unable to supinate when the elbow is extended.
The radial nerve passes down the spiral groove of the humerus and enters the supinator muscle, dividing into deep and superficial sensory branches. This division of the radial nerve can lead to entrapment and compression of the deep branch, causing selective paralysis of the muscles served by this nerve. This nerve syndrome is known as supinator entrapment syndrome or radial tunnel syndrome.
Supinator entrapment syndrome can be caused by compression from various soft-tissue masses surrounding the nerve or stress caused by repetitive supination and pronation movements. The radial nerve can be surgically explored and released through dorsal or anterior approaches, with surgical treatment generally being successful.
The supinator muscle is innervated by the deep branch of the radial nerve, which becomes the posterior interosseous nerve upon exiting the muscle. This nerve supplies the triceps muscle, extensors of the wrist, and the extensors of the fingers and thumb.
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Supination is important for daily activities, like turning a screwdriver
The ability to supinate is essential for performing various daily tasks, such as turning a screwdriver. Supination is a movement unique to the forearms and hands, allowing the palm to face upwards. This movement is facilitated by the supinator muscle of the forearm and the biceps brachii of the upper arm, which work together to rotate the radius bone.
The supinator muscle is located in the posterior compartment of the forearm and consists of two layers of fibres. The deep branch of the radial nerve passes through the supinator muscle, supplying motor function to the extensor muscles and the abductor pollicis longus. The supinator muscle is responsible for approximately half of the power generated during supination, with the other half contributed by the biceps brachii.
During activities like turning a screwdriver, supination is crucial for generating the necessary force and stability. The triceps muscle, located at the back of the arm, straightens the elbow, allowing for a pushing motion. Without supination, the bending action of the biceps would cause the elbow to bend with each twist, hindering the ability to effectively turn a screwdriver.
In addition to the supinator and biceps brachii muscles, other muscles involved in supination include the brachialis and brachioradialis. These muscles work synergistically with the supinator and biceps brachii to produce a smooth and controlled supination movement.
While supination is essential for daily activities, it is important to be mindful of potential injuries. The radial nerve, which supplies the supinator muscle, is susceptible to entrapment and compression. Repetitive supination and pronation movements can lead to stress on the nerve, potentially resulting in selective paralysis of the muscles it innervates. Therefore, it is crucial to maintain a healthy balance of movements and avoid excessive strain on any single motion.
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Frequently asked questions
Supination is the movement of the forearm that turns the palm to face upwards.
The supinator muscle of the forearm and the biceps brachii of the upper arm are involved in supination. The supinator muscle is located just below the elbow and provides about half the power of the bicep muscle for supination.
The supinator muscle supinates the forearm by pulling on the radius. It consists of two layers of fibres that originate from the supinator crest of the ulna, the lateral epicondyle of the humerus, the radial collateral ligament, and the annular radial ligament.
