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Brachialis: location under the biceps, origin, insertion and nerve

Where is the brachialis?

When you make a muscle, the bulge is the biceps. What lies right underneath it? Lift the biceps away and you find a broad muscle lying flat on the humerus: the brachialis.

teamLabBody with the brachialis selected (front view), running from the lower half of the humerus across the front of the elbow
Screen from teamLabBody Pro, an anatomy app ›

It occupies the lower half of the front of the upper arm. It is wider and flatter than the biceps, and from the surface you see only the parts that show at its lateral and medial edges.

Origin, insertion and nerve

・Origin: lower half of the anterior humerus (below the deltoid attachment) and the medial and lateral intermuscular septa

・Insertion: coronoid process and tuberosity of the ulna

・Nerve: musculocutaneous nerve (C5–C6); the lateral part often also receives a branch from the radial nerve

・Action: flexion of the elbow

While the biceps runs from the scapula to the radius, the brachialis runs from the humerus to the ulna. It does not cross the shoulder; it crosses only the elbow. Textbooks differ in whether they mention the radial nerve contribution.

How it differs from the biceps

teamLabBody with the brachialis (yellow) selected and the biceps brachii shown in front of it
Screen from teamLabBody Pro, an anatomy app ›

Here the biceps brachii is shown in front of the brachialis (yellow), covering it. Both flex the elbow, but the biceps inserts on the radius and also supinates the forearm; with the palm turned down it flexes less effectively. The brachialis inserts on the ulna, which does not move when the forearm rotates, so it flexes the elbow equally well whichever way the palm faces. With the brachioradialis, these are the three main elbow flexors.

The musculocutaneous nerve

The musculocutaneous nerve leaves the brachial plexus, pierces the coracobrachialis, and runs down between the biceps and brachialis, supplying all three before continuing as the lateral cutaneous nerve of the forearm. So all the anterior arm muscles are supplied by the musculocutaneous nerve, while the triceps brachii at the back is supplied by the radial nerve.

Name and terms

Brachialis comes from the Latin bracchium, arm, and means of the arm. It shares its root with biceps brachii and brachioradialis, so the spellings are easy to mix up. The Latin is musculus brachialis.

See it in the app

Hidden under the biceps, the brachialis shows only partly in anterior views. In the 3D anatomy app teamLabBody you can hide the biceps, keep just the brachialis, and rotate it to see where it arises on the humerus and how it crosses the elbow to the ulna. Show the biceps again to see how the two overlap. Cross sections are available with the PREMIUM plan.

FAQ

Where is the brachialis?
At the front of the upper arm, deep to the biceps. It arises from the lower half of the front of the humerus and inserts on the ulna.
How is the brachialis different from the biceps?
The biceps runs from the scapula to the radius and also supinates. The brachialis runs from the humerus to the ulna, crosses only the elbow, and flexes it whichever way the palm faces.
Which nerve supplies the brachialis?
The musculocutaneous nerve (C5–C6), often with a small radial nerve branch to its lateral part.

Related articles

・Biceps brachii: lies in front of the brachialis

・Brachioradialis: the elbow flexor along the lateral forearm

・Coracobrachialis: pierced by the musculocutaneous nerve

・Triceps brachii: extends the elbow at the back of the arm

・Ulna: the forearm bone the brachialis inserts on

・All muscles of the body

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