Logan Steele
The ulna is one of two long bones in the forearm, stretching from the elbow to the wrist. It is involved in motions assisted by the elbow and wrist joints, helping the forearm, wrist, and hand to move, flex, and rotate. The ulna is also a site of attachment for many muscles, including the triceps brachii, flexor digitorum profundus, and pronator quadratus. The olecranon is a large projection of bone at the proximal end of the ulna, forming part of the trochlear notch and serving as the point of insertion for the triceps brachii muscle. The coronoid process is another prominent feature of the ulna, projecting forward from the upper and front part of the bone. The brachialis muscle attaches to the tuberosity of the ulna, which is a roughening immediately distal to the coronoid process.
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What You'll Learn
Triceps Brachii
The triceps brachii is a three-headed muscle in the arm, consisting of the long, medial, and lateral head. It is the only constituent of the arm's posterior muscle group, spanning almost the entire length of the humerus. The triceps brachii is the only muscle in the arm's posterior compartment.
The triceps brachii is responsible for extension of the forearm at the elbow joint. The long head also contributes to the extension and adduction of the arm at the shoulder joint. The triceps brachii contracts when the elbow is straightened and expands when the elbow is bent. The muscle can be worked out in isolation or with compound elbow extension movements. Isolation exercises include cable push-downs, lying triceps extensions, and arm extensions behind the back. Examples of compound exercises include pressing movements like push-ups, bench presses, and dips.
The triceps brachii is innervated by the radial nerve, which gives off a separate branch for each head. The C6 root value of the radial nerve innervates the lateral head, the C7 root value innervates the long head, and the C8 root value supplies the medial head. However, some studies have found that the long head of the triceps brachii is innervated by the axillary nerve in around 14% of individuals, and in 3% of people, the radial nerve and axillary nerve provide dual innervation. The muscle is supplied with oxygen and nutrients from the branches of the deep brachial artery.
The triceps brachii is an important surgical landmark as it plays a role in creating anatomical spaces that are traversed by neurovascular structures. The medial head of the triceps brachii is used for precise, low-force movements, while the lateral head is used for high-intensity force movements.
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Brachialis
The ulna is one of the two long bones in the forearm, the other being the radius. It is the medial bone of the forearm, running parallel to the radius and stretching from the elbow to the wrist. The ulna is slightly longer and thinner than the radius. The ulna serves as the origin and insertion site for more than a dozen muscles.
The brachialis is a muscle in the upper arm that flexes the elbow. It is the prime mover of elbow flexion, generating about 50% more power than the biceps. The brachialis is the only pure flexor of the elbow joint, producing the majority of force during elbow flexion. It is not affected by pronation or supination of the forearm and does not participate in pronation and supination due to its lack of attachment to the radius. The muscle is located in the anterior compartment of the arm, deep to the biceps brachii, and makes up part of the floor of the region known as the cubital fossa (elbow pit).
The brachialis is innervated by the musculocutaneous nerve, which runs on its superficial surface, between it and the biceps brachii. In 70-80% of people, the muscle has double innervation with the radial nerve. The brachialis is supplied by muscular branches of the brachial artery and by the recurrent radial artery. The muscle is occasionally doubled, with additional muscle slips to the supinator, pronator teres, biceps brachii, lacertus fibrosus, or radius.
The brachialis originates from the anterior surface of the distal half of the humerus, near the insertion of the deltoid muscle, which it embraces by two angular processes. Its origin extends below to within 2.5 cm of the margin of the articular surface of the humerus at the elbow joint. Its fibres converge to a thick tendon, which is inserted into the tuberosity of the ulna and the rough depression on the anterior surface of the coronoid process of the ulna.
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Flexor Carpi Ulnaris
The flexor carpi ulnaris (FCU) is a muscle in the forearm that flexes and adducts the hand at the wrist joint. It is the most powerful wrist flexor and is the only anterior forearm muscle completely innervated by the ulnar nerve. The FCU tendon is a landmark for locating the ulnar nerve and artery during surgery.
The FCU is a fusiform muscle located in the anterior compartment of the forearm. It is one of the superficial flexors of the forearm, along with the pronator teres, palmaris longus, flexor digitorum superficialis, and flexor carpi radialis. The FCU is the most medial of the superficial flexors. It originates from two separate heads, the humeral and ulnar head, which are connected by a tendinous arch. The humeral head originates from the medial epicondyle of the humerus via the common flexor tendon. The ulnar head originates from the olecranon and the proximal part of the dorsal border of the ulna by an aponeurosis.
The FCU inserts onto the pisiform, hook of the hamate, and the anterior surface of the base of the fifth metacarpal. The muscle is attached to the hook of the hamate via the pisohamate ligament and the fifth metacarpal bone through the pisometacarpal ligament. The FCU is innervated by the ulnar nerve's muscular branch, which arises from the C7 and C8 nerve roots. The ulnar nerve enters the forearm between the two heads of the FCU.
The FCU can be strengthened by exercises that resist its flexion, such as wrist rollers and wrist curls with dumbbells. These exercises help to prevent injury to the ulnar collateral ligament of the elbow joint.
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Extensor Carpi Ulnaris
The extensor carpi ulnaris (ECU) is a skeletal muscle located on the ulnar side of the forearm. It is a key contributor to the extension and adduction of the wrist, playing a crucial role in various activities involving these movements. The ECU is the most medial muscle of the posterior forearm, originating from the lateral epicondyle of the distal humerus and the posterior aspect of the ulna. It inserts onto the dorsal base of the fifth metacarpal, extending the wrist and, when acting alone, inclining the hand toward the ulnar side.
The ECU is a fusiform muscle, spanning between the elbow and base of the little finger. It is a part of the superficial forearm extensor group, which includes muscles such as the anconeus, brachioradialis, extensor carpi radialis longus, and extensor digitorum. The ECU works together with the extensor carpi radialis brevis and extensor carpi radialis longus to achieve a balanced extension of the wrist without deviating the hand in the transverse plane. This is particularly important for activities that require a strong grip, such as clenching a fist or making a power grip.
The ECU is innervated by the posterior interosseous nerve (C7 and C8), a branch of the deep division of the radial nerve. The radial nerve itself stems from the posterior cord of the brachial plexus. The blood supply to the ECU is provided by branches of the radial recurrent and posterior interosseous arteries, which originate from the radial and ulnar arteries, respectively.
The ECU is clinically significant due to its role in wrist and forearm function and its susceptibility to injuries. Athletes who engage in activities requiring forceful wrist movements are particularly prone to ECU injuries. These injuries may result from repetitive stress on the tendon during activities such as gripping, throwing, or racket sports. Tennis elbow is a common injury associated with the ECU, occurring in individuals who participate in activities with repetitive arm, elbow, and wrist movements, especially when tightly gripping an object. Treatment options for tennis elbow include occupational therapy, physical therapy, anti-inflammatory medication, and rest from the aggravating activity.
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Flexor Digitorum Profundus
The ulna is one of the two long bones in the forearm, the other being the radius. The ulna is the medial bone of the forearm, running from the elbow to the wrist, parallel to the radius. The ulna is involved in movements assisted by the elbow and wrist joints.
The flexor digitorum profundus is a muscle in the forearm that is responsible for flexing the fingers. It is an extrinsic hand muscle, with its muscle belly located in the forearm. The flexor digitorum profundus is a fusiform muscle, located deep within the anterior (flexor) compartment of the forearm. It is considered a deep muscle of the anterior compartment (deep volar compartment) of the forearm. The muscle extends from the proximal part of the ulna to the distal phalanges of the second to fifth digits. The muscle fibres are arranged so that the medial part of the muscle inserts into the fourth and fifth digits, while the lateral part inserts into the second and third digits.
The flexor digitorum profundus is the most powerful and bulky muscle of the forearm. It is the main gripping muscle of the hand, as the tendons of the flexor digitorum profundus arise at or below the wrist joint. The muscle is also involved in flexion of the midcarpal (wrist), metacarpophalangeal, and proximal interphalangeal joints of the index, middle, ring, and little fingers. The flexor digitorum profundus also aids the lumbrical muscles in their role as extensors of the interphalangeal joints. The lumbricals are intrinsic muscles of the hand that attach to the tendon of the flexor digitorum profundus.
The flexor digitorum profundus originates from four sites: the superior three-quarters of the anterior surface of the ulna, the adjacent part of the interosseous membrane, the coronoid process of the ulna, and the aponeurosis of the flexor carpi ulnaris muscle. The muscle takes an inferior course towards the hand, giving off a broad tendon at the level of the distal third of the forearm. This tendon crosses the superficial surface of the pronator quadratus and enters the hand by passing beneath the flexor retinaculum. Upon entering the hand, the tendon splits into four slips that attach to the palmar surfaces of the bases of the distal phalanges of the second to fifth digits.
The flexor digitorum profundus is supplied by the anterior interosseous artery, a branch of the common interosseous artery. The muscle is also accompanied by the palmar interosseous branch of the median nerve. The flexor digitorum profundus lymphatic drainage is part of the upper limb lymph system, consisting of superficial and deep lymphatic vessels.
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Frequently asked questions
The ulna is a long bone in the forearm stretching from the elbow to the wrist. It is on the same side of the forearm as the little finger, running parallel to the radius, the forearm's other long bone.
The triceps brachii muscle attaches to the olecranon, a bony process at the proximal end of the ulna. The brachialis muscle attaches to the tuberosity of the ulna, a roughening immediately distal to the coronoid process. The flexor digitorum profundus and the pronator quadratus have origin sites on the ulna. The flexor carpi ulnaris, extensor carpi ulnaris, and flexor digitorum profundus have attachment sites on the ulna.
The ulna assists in pronation and supination of the forearm and hand. It also helps you move your arm, wrist, and hand.
A fractured ulna will usually require immobilization with a splint or cast. In some cases, surgery may be necessary to realign the bone. Physical therapy may also be needed to regain strength and mobility.
