Triceps brachii: origin, insertion, action and innervation
The triceps brachii has three heads, from the scapula and the back of the humerus, and inserts on the olecranon of the ulna. It extends the elbow and is supplied by the radial nerve.
Quick answer
- Latin name
- Musculus triceps brachii
- Origin
- Long head: infraglenoid tubercle of the scapula. Lateral head: back of the humerus, above the radial groove. Medial head: back of the humerus, below the radial groove
- Insertion
- Olecranon of the ulna
- Action
- Extends the elbow; the long head also extends and adducts the shoulder
- Innervation
- Radial nerve (C6–C8)
- Blood supply
- Deep artery of the arm (profunda brachii)
The triceps brachii fills the whole back of the upper arm. It is the antagonist of the biceps and brachialis: when they bend the elbow, the triceps straightens it.
Where it is
The triceps is the only muscle of the posterior compartment of the arm. Its three heads cover the back of the humerus from the shoulder to the elbow, and come together in a broad tendon that ends on the point of the elbow.
Origin and insertion
- The long head arises from the infraglenoid tubercle, just below the socket of the shoulder joint. It's the only head that crosses the shoulder.
- The lateral head arises from the back of the humerus, above the spiral (radial) groove.
- The medial head arises from the back of the humerus below that groove. It lies deepest and is mostly covered by the other two.
- All three insert on the olecranon, the bony point of the elbow on the ulna.
The radial nerve runs in the groove between the lateral and medial head origins, which is why that groove is called the radial groove.
What it does
- Elbow extension: the triceps straightens the elbow, as in a push-up or pushing a door open. The medial head is active in almost every extension; the long and lateral heads join in when more force is needed.
- Shoulder extension and adduction: the long head helps pull the arm back and towards the body, and steadies the head of the humerus.
Innervation and blood supply
All three heads are supplied by the radial nerve (roots C6 to C8). The main artery is the deep artery of the arm (profunda brachii), which travels with the radial nerve in the radial groove.
How to remember it
- "Triceps, three heads, one job: straighten the elbow."
- The radial nerve "splits" the lateral and medial heads: lateral above the groove, medial below.
- Long head = long way, from the scapula, so it also moves the shoulder.
Frequently asked questions
What are the three heads of the triceps?
The long head (from the scapula), the lateral head and the medial head (both from the back of the humerus).
Where does the triceps insert?
On the olecranon of the ulna, the bony point of the elbow.
Which nerve supplies the triceps?
The radial nerve, from spinal roots C6 to C8.
Which head of the triceps crosses the shoulder?
Only the long head, because it is the only one that starts on the scapula.