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The elbow is a synovial joint that connects the arm to the forearm. It is marked by the medial and lateral epicondyles, and the olecranon process. The elbow muscles are commonly referred to as flexors or extensors, depending on how they affect elbow movement. Extensors are on the inside of the arm and help extend the arm outward. The elbow extensor muscles are the triceps brachii and the anconeus. These muscles work together to increase the angle between the humerus and the ulna and radius, straightening the arm. The radial nerve supplies all muscles that extend the elbow and wrist.
| Characteristics | Values |
|---|---|
| Elbow extensor muscles | Triceps brachii, Anconeus |
| Elbow flexor muscles | Biceps brachii, Brachialis, Brachioradialis |
| Elbow joint | Hinge-type synovial joint |
| Elbow innervation | Musculocutaneous nerve, Radial nerve, Median nerve, Ulnar nerve |
| Elbow ligaments | Radial collateral ligament, Ulnar collateral ligament |
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What You'll Learn
Triceps brachii
The triceps brachii is a three-headed muscle (Latin for "three-headed muscle of the arm") found on the back of the upper arm in vertebrates. It is the only muscle in the arm's posterior compartment. It consists of the long, medial, and lateral heads, which all cross the elbow joint. The triceps brachii is responsible for extending the forearm at the elbow joint and stabilising the elbow during fine movements, such as writing.
The long head of the triceps brachii arises from the infraglenoid tubercle of the scapula, which is a rough area at the inferior margin of the glenoid fossa. It contributes to the extension and adduction of the arm at the shoulder joint, receiving an additional contraction when the arm is behind the torso. The medial head arises proximally in the humerus, just below the groove of the radial nerve, and its distal part arises from the dorsal surface of the humerus. The lateral head originates from a narrow, linear ridge on the posterior surface of the humerus, superior to the radial groove.
The triceps brachii is innervated by the radial nerve, which provides a separate branch for each head. The C6 root value innervates the lateral head, C7 innervates the long head, and C8 supplies the medial head. However, studies have found that in some individuals, the long head is innervated by the axillary nerve or receives dual innervation from both the radial and axillary nerves. The triceps brachii is supplied with oxygen and nutrients by the branches of the deep brachial artery.
The triceps brachii can be exercised through isolation or compound elbow extension movements, such as cable push-downs, lying triceps extensions, and arm extensions behind the back. It can also be trained to contract statically to keep the arm straight against resistance.
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Anconeus
The anconeus is a small, triangular muscle located at the elbow, attaching the humerus and ulna. It is part of the superficial extensor compartment. The anconeus muscle is active during elbow extension, but its importance in this movement is considered minor compared to the triceps brachii muscle, which is the major muscle responsible for elbow extension.
The anconeus originates at the dorsal side of the lateral epicondyle of the humerus and inserts at the olecranon of the ulna, along the proximal third of the posterior face of the ulna. The anconeus muscle is supplied by a motor branch of the radial nerve (C6-C8), arising from the radial sulcus of the humerus. It can be easily palpated at the lateral side of the forearm near the elbow, especially during pronation and supination movements.
Functionally, the anconeus is believed to be a continuation of the triceps brachii muscle, as they share similar functions and are often partially or completely blended together. The contraction of the anconeus leads to the extension of the forearm at the elbow, and it also provides support for the dorsal joint capsule and the ulna. This helps prevent damage during hyperextension.
The anconeus muscle can be affected by cubital tunnel syndrome, which may be caused by its hypertrophy. This can result in numbness of the ulnar side of the hand, pain in the elbow, and sensory changes in the ulnar nerve distribution. Additionally, trauma to the nerve supply of the anconeus muscle can occur due to shoulder dislocation or fractures of the upper part of the humerus or olecranon.
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Radial nerve
The radial nerve is a major peripheral nerve of the upper limb that supplies the posterior portion of the upper limb. It is one of five nerve branches that extend from the brachial plexus, which is a network of nerves that originate from the spinal cord. The radial nerve carries fibres from the posterior roots of spinal nerves C5, C6, C7, C8, and T1.
The radial nerve takes a winding path from the lower armpit to the fingers, supplying movement and sensory function to parts of the arm, forearm, wrist, and hand. It wraps around the humerus, the long upper arm bone that runs from the shoulder to the elbow, and travels downwards together with the profunda brachii artery. It then enters the forearm by travelling anterior to the lateral epicondyle of the humerus, through the cubital fossa.
The radial nerve provides motor innervation to the triceps brachii and the anconeus muscles, which are involved in extending the elbow. It also provides cutaneous sensory innervation to most of the back of the hand, including the web of skin between the thumb and index finger, except for the back of the little finger and adjacent half of the ring finger, which are supplied by the ulnar nerve.
The radial nerve divides into two branches: the deep branch (motor) and the superficial branch (sensory). The deep branch innervates the muscles in the posterior compartment of the forearm, while the superficial branch contributes to the cutaneous innervation of the dorsal hand and fingers. The deep branch also pierces the supinator muscle and is renamed the posterior interosseous nerve.
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Biceps brachii
The biceps brachii, commonly known as the biceps, is a large, thick muscle on the front of the upper arm between the shoulder and the elbow. It is composed of a short head and a long head. The long head is located on the lateral side of the biceps brachii, while the short head is located on the medial side. The short head is sometimes referred to as "caput breve", while the long head is also called "caput longum".
The biceps brachii works across three joints and is able to generate movements in the glenohumeral, elbow, and radio-ulnar joints. It functions as a powerful supinator of the forearm, i.e. it turns the palm upwards. This action is aided by the supinator muscle and requires the elbow to be at least partially flexed. The biceps are involved in tasks such as lifting, sports involving throwing and racket use, and gesturing.
The biceps brachii is also an important landmark for locating the brachial artery during physical examination and ultrasound-guided arterial cannulation. Conditions affecting the biceps brachii are often caused by muscle overuse or trauma. For example, the "popeye deformity," common to baseball pitchers, arises from a ruptured long head tendon due to chronic wear and tear. Consequently, the muscle forms a ball at the anterior mid-arm.
The biceps brachii is innervated by the musculocutaneous nerve C5, C6, and C7. The primary arterial blood supply for the biceps brachii muscle comes from the muscular branches of the brachial artery. This artery is the axillary artery's continuation as it exits the axilla at the teres major's inferior margin.
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Brachialis
The brachialis is a muscle in the upper arm that flexes the elbow. It is the primary flexor of the elbow and is located deep to the biceps brachii. The brachialis is the prime mover of elbow flexion, generating about 50% more power than the biceps. It is innervated by the musculocutaneous nerve and occasionally receives additional innervation from the radial nerve. In 70-80% of people, the muscle has double innervation with the radial nerve. 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 brachialis is located in the anterior compartment of the arm, also known as the flexor compartment. It is fusiform in shape and is a broad muscle, with its broadest part located in the middle rather than at either of its extremities. The brachialis is occasionally doubled, with additional muscle slips to the supinator, pronator teres, biceps brachii, lacertus fibrosus, or radius. It is supplied by muscular branches of the brachial artery and by the recurrent radial artery. The brachialis acts as the floor of the cubital fossa, also known as the elbow pit, and is part of the radial tunnel.
The brachialis originates from the anterior surface of the distal half of the humerus, just distal to the insertion of the deltoid muscle. Its origin extends below to within 2.5 cm of the margin of the articular surface of the humerus at the elbow joint. The fibres of the brachialis 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. The tendon of the brachialis forms part of the floor of the cubital fossa.
The brachialis can be commonly injured by repetitive forceful contractions or muscular contractions with the arm in hyperextension. This is commonly seen in climbers due to the pronation of the hand and the extended starting position. Physical activity that involves a lot of pull-ups, curls, and rope climbing can also cause brachialis muscle pain. A strain to the brachialis tendon can cause a lack of elbow extension due to painful end-range stretching of the tendon.
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Frequently asked questions
The muscles that extend the elbow are the triceps brachii and the anconeus.
The triceps brachii is a long muscle that runs from the scapula to the ulna. It works to extend the arm and stabilize the elbow during fine movements.
The anconeus is a small muscle that begins at the distal end of the humerus and ends at the olecranon. It helps extend the forearm at the elbow.
Yes, the radial nerve supplies all muscles that extend the elbow and wrist, including the supinator and brachioradialis muscles.
Extensors are on the inside of the arm and help extend the arm outward. Flexors are at the back of the elbow and pull the arm closer to the body by bending the elbow.
