Posterior Forearm Flashcards
What are the muscles in the superficial compartment?
- brachioradialis
- extensor carpi radialis longus and brevis
- extensor digitorum
- extensor carpi ulnaris
- extensor digiti minimi
- anconeus
What are the muscles in the deep component?
- abductor pollicis longus
- extensor pollicis brevis
- extensor pollicis longus
- extensor indicis
- supinator
Give the origins, insertions and actions of Brachioradialis
The muscle is most visible when the forearm is half pronated, and flexing at the elbow against resistance.
In the distal forearm, the radial artery and nerve are sandwiched between the brachioradialis and the deep flexor muscles.
Attachments: Originates from the proximal aspect of the lateral supraepicondylar ridge of humerus, and attaches to the distal end of the radius, just before the radial styloid process.
Actions: Flexes at the elbow.
Innervation: Radial nerve.
Give the origins, insertions and actions of Carpi Radialis Longus and Brevis
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.
Attachments: The ECRL originates from the supracondylar ridge, while the ECRB originates from the lateral epicondyle. Their tendons attach to metacarpal bones II and III.
Actions: Extends and abducts the wrist.
Innervation: Radial nerve.
Give the origins, insertions and actions of Extensor Digitorum
The extensor digitorum is the main extensor of the fingers. To test the function of the muscle, the forearm is pronated, and the fingers extended against resistance.
Attachments: Originates from the lateral epicondyle. The tendon continues into in the distal part of the forearm, where it splits into four, and inserts into the extensor hood of each finger.
Actions: Extends medial four fingers at the MCP and IP joints.
Innervation: Radial nerve.
Give the origins, insertions and actions of Extensor Digiti Minimi
The extensor digiti minimi is thought to originate from the extensor digitorum muscle. In some people, these two muscles are fused together. Anatomically, the extensor digiti minimi lies medially to the extensor digitorum.
Attachments: Originates from the lateral epicondyle of the humerus. It attaches, with the extensor digitorum tendon, into the extensor hood of the little finger.
Actions: Extends the little finger, and contributes to extension at the wrist.
Innervation: Radial nerve.
Give the origins, insertions and actions of Extensor Carpi Ulnaris
The extensor carpi ulnaris is located on the medial aspect of the posterior forearm. Due to its position, it is able to produce adduction as well as extension at the wrist.
Attachments: Originates from the lateral epicondyle of the humerus, and attaches to the base of metacarpal V.
Actions: Extension and adduction of wrist.
Innervation: Radial nerve.
Give the origins, insertions and actions of Anconeus
The aconeus is situated medially and superiorly in the extensor compartment of the forearm. It is blended with the fibres of the triceps brachii, and the two muscles can be indistinguishable.
Attachments: Originates from the lateral epicondyle, and attaches to the posterior and lateral part of the olecrannon.
Actions: Moves the ulna during pronation and extends at the elbow joint.
Innervation: Radial nerve.
Give the origins, insertions and actions of Supinator
he supinator lies in the floor of the cubital fossa. It has two heads, which the deep branch of the radial nerve passes between.
Attachments: It has two heads of origin. One originates from the lateral epicondyle of the humerus, the other from the posterior surface of the ulna. They insert together into the posterior surface of the radius.
Actions: Supinates the forearm.
Innervation: Radial nerve.
Give the origins, insertions and actions of Abductor Pollicis Longus
The abductor pollicis longus is situated immediately distal to the supinator muscle. In the hand, its tendon contributes to the lateral border of the anatomical snuffbox.
Attachments: Originates from the interosseous membrane and the adjacent posterior surfaces of the radius and ulna. It attaches to the lateral side of the base of metacarpal I.
Actions: Abducts the thumb.
Innervation: Radial nerve.
Give the origins, insertions and actions of Extensor Pollicis Brevis
The extensor pollicis brevis can be found medially and deep to the abductor pollicis longus. In the hand, its tendon contributes to the lateral border of the anatomical snuffbox.
Attachments: Originates from the posterior surface of the radius and interosseous membrane. It attaches to the base of the proximal phalanx of the thumb.
Actions: Extends at the metacarpophalangeal and carpometacarpal joints of the thumb.
Innervation: Radial nerve.
Give the origins, insertions and actions of Extensor Pollicis Longus
The extensor pollicis longus muscle has a large muscle belly than the EPB. Its tendon travels medially to the dorsal tubercle at the wrist, using the tubercle as a ‘pulley’ to increase the force exerted.
The tendon of the extensor pollicis longus forms the medial border of the anatomical snuffbox in the hand.
Attachments: Originates from the posterior surface of the ulna and interosseous membrane. It attaches to the distal phalanx of the thumb.
Actions: Extends all joints of the thumb: carpometacarpal, metacarpophalangeal and interphalangeal.
Innervation: Radial nerve.
Give the origins, insertions and actions of Extensor Indicus Proprius
This muscle allows the index finger to be independent of the other fingers during extension.
Attachments: Originates from the posterior surface of the ulna and interosseous membrane, distal to the extensor pollicis longus. Attaches to the extensor hood of the index finger.
Actions: Extends the index finger.
Innervation: Radial nerve.
