Dominic Stone
The triceps brachii is a large, thick muscle on the dorsal part of the upper arm in humans. It is a three-headed muscle, with three muscle segments: the long head, the lateral head, and the medial head. The triceps brachii is the only muscle in the posterior compartment of the arm, and it is responsible for the extension of the forearm at the elbow joint. The three heads of the triceps brachii originate at different locations and converge onto a common tendon, which inserts into the ulna bone in the forearm. The triceps brachii is a voluntary muscle that can be contracted to straighten the elbow and is important for everyday movements such as reaching and pushing off from armrests.
| Characteristics | Values |
|---|---|
| Common name | Tricep |
| Scientific name | Triceps brachii |
| Number of heads | Three |
| Head names | Long, lateral, and medial |
| Location | Back of the upper arm |
| Shape | Horseshoe |
| Function | Extension of the elbow joint |
| Innervation | Radial nerve |
| Blood supply | Deep brachial artery and superior ulnar collateral artery |
| Tendon attachment site | Olecranon process of the ulna |
| Common injuries | Tendonitis, strains, sprains, tears |
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What You'll Learn
Triceps brachii: a three-headed muscle
The triceps brachii is a three-headed muscle, with the Latin name literally translating to "three-headed muscle of the arm". It is a large, thick muscle on the dorsal part of the upper arm, often appearing as a horseshoe shape on the posterior aspect of the arm. The three muscle segments of the triceps include the long head, the lateral head, and the medial head. Each of these three heads originates at a different location.
The long head originates at the infraglenoid tubercle, a ridge along the outermost portion of the scapula (shoulder blade) that connects with the humerus to form the shoulder joint. The medial head arises proximally in the humerus, just inferior to the groove of the radial nerve, and its attachment extends over an elongated triangular area on the humerus. The apex of the triangle is located on the medial border of the humerus above the insertion of the teres major, while the base connects the medial and lateral epicondyles of the humerus. The lateral head originates from a narrow, linear ridge on the posterior surface of the humerus, just superior to the radial groove.
All three muscle bellies converge onto a common tendon, which inserts onto the olecranon process of the ulna, one of the bones in the forearm. The main function of the triceps is the extension of the elbow joint, which causes the elbow to straighten. The triceps brachii is innervated by the radial nerve, which gives off a separate branch for each head. The triceps is a voluntary muscle, meaning it is a muscle that humans choose to move.
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Triceps anatomy
The triceps, or triceps brachii, is a large, thick muscle on the dorsal part of the upper arm in humans. It often appears as the shape of a horseshoe on the posterior aspect of the arm. The triceps is an extensor muscle of the elbow joint and an antagonist of the biceps and brachialis muscles. It can also fixate the elbow joint when the forearm and hand are used for fine movements, such as writing. The triceps is a voluntary muscle, meaning it is a muscle that a person can choose to move.
The triceps is a three-headed muscle, with three muscle bellies or points of origin, which is where it gets its name—'tri' meaning three, and 'ceps' coming from 'caput', the Latin for head. These three heads are the medial head, the lateral head, and the long head. The long head is involved in retroversion and adduction of the arm. It helps stabilise the shoulder joint at the top of the humerus. The medial head does not attach to the scapula and therefore has no action on the glenohumeral joint. The lateral head is active during extension of the forearm at the elbow joint when the forearm is supinated or pronated.
The triceps tendon attaches to the olecranon process, the pointy projection at the end of the ulna bone of the forearm that forms the elbow. All three muscle heads of the triceps run down the back of the arm and join close to the elbow to form one common tendon. The triceps is located at the back of the upper arm and covers the majority of the backside of the humerus (upper arm bone). Each of the three heads of the triceps originates at a different location. The long head originates at the infraglenoid tubercle, a ridge along the outermost portion of the shoulder blade that connects with the humerus to form the shoulder joint. The medial head and lateral head start at the medial (inner) and lateral (outer) sides of the upper portion of the humerus.
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, root value C7 innervates the long head, and root value C8 supplies the medial head. The triceps brachii muscle is mainly supplied by the deep brachial artery and the superior ulnar collateral artery, which arises from the brachial artery.
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Triceps tendon
The triceps brachii is a three-headed muscle in the arm, with long, medial, and lateral heads. The triceps tendon is the point at which these three heads come together and attach to the ulna in the forearm. The triceps tendon is also referred to as the distal triceps tendon, as it is located some distance from the point of origin of the muscle.
The triceps tendon is responsible for elbow extension. The long head of the triceps also assists with the extension and adduction of the arm at the shoulder joint. The triceps tendon is innervated by the radial nerve, which gives off separate branches for each head. The tendon is also vascularly supplied by the brachial artery.
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Triceps heads: long, lateral, and medial
The triceps brachii is a three-headed muscle of the arm, with the heads known as the long, lateral, and medial. These heads originate from their respective attachments on the humerus and scapula, and converge onto a common tendon that inserts on the ulna. The triceps brachii is the only constituent of the posterior muscle group of the arm, spanning almost the entire length of the humerus.
The long head of the triceps arises from the infraglenoid tubercle of the scapula, which is a rough area at the inferior margin of the glenoid fossa. It extends slightly above to the adjacent glenoid labrum and blends with the glenohumeral capsule of the shoulder joint, contributing to its stability. The long head can be palpated as an elevation parallel and medial to the posterior border of the deltoid muscle when the elbow is extended. It also assists with the extension and adduction of the arm at the shoulder joint.
The lateral head originates from a narrow, linear ridge on the posterior surface of the humerus, just superior to the radial groove. Its attachment ascends obliquely, beginning from the lateral border of the humerus behind the deltoid tuberosity. The lateral head is also active during extension of the forearm at the elbow joint when the forearm is supinated or pronated.
The medial head has a broad origin along the entire posterior surface of the humerus inferior to the radial groove. It is overlapped by the long and lateral heads of the triceps. The medial head has an additional attachment to the posterior aspect of the medial and lateral intermuscular septum. The medial head enables more precise, low-force movements.
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Triceps functions
The triceps brachii is a large, thick muscle on the dorsal part of the upper arm. It often appears as a horseshoe shape on the posterior aspect of the arm. The triceps is an extensor muscle of the elbow joint and an antagonist of the biceps and brachialis muscles. It can also fixate the elbow joint when the forearm and hand are used for fine movements, such as writing.
The triceps muscle is a main muscle of the upper arm, running from the top of the shoulder to the elbow at the back of the arm. When the triceps contracts, it causes the elbow to straighten. The triceps is a voluntary muscle, made up of skeletal muscle fibres that contract under conscious control. It is a fusiform, or spindle-shaped, muscle that is wider in the middle and narrower at each end.
The triceps is composed of three heads: the long, lateral, and medial head. These heads converge into a single tendon that attaches to the ulna, one of the bones in the forearm. The triceps muscle is responsible for the extension of the elbow joint and straightening of the arm. It also plays a significant role in the stability and strength of the shoulder. The triceps' position and function are critical for sustaining upper body strength and facilitating coordinated arm movements.
The long head of the triceps arises from the infraglenoid tubercle of the scapula. It extends distally anterior to the teres minor and posterior to the teres major. The medial head arises proximally in the humerus, just inferior to the groove of the radial nerve. The lateral head originates from a narrow, linear ridge on the posterior surface of the humerus, just superior to the radial groove.
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Frequently asked questions
The tricep, or triceps brachii, is a large muscle on the back of the upper arm in humans. It is made up of three muscle segments, or heads: the long head, the lateral head, and the medial head.
The tricep is located on the dorsal part of the upper arm, running from the shoulder to the elbow at the back of the arm.
The tricep is an extensor muscle of the elbow joint, meaning it is responsible for the extension, or straightening, of the forearm at the elbow joint. It also plays a role in stabilising the shoulder joint and creating anatomical spaces for neurovascular structures.
The tricep originates at the scapula (shoulder blade) and the humerus (upper arm bone). It inserts onto the olecranon process of the ulna, one of the bones in the forearm.
To palpate the tricep, the patient should be in a high sitting position. For the medial head, place your three fingers just above the medial epicondyle and instruct the patient to extend the elbow pushing downward. For the long head, place your three fingers just beneath the axilla posteriorly and instruct the patient to extend the elbow. For the lateral head, place your three fingers to the postero-lateral side in the middle of the shaft of the humerus.
