Hi, everyone. This is Matt from Kenhub! And in this tutorial, we will discuss the origin, insertion, innervation, and function of the brachialis muscle.
The brachialis is a long, strong muscle of the upper arm. For the most part, the brachialis is buried under the biceps brachii and is therefore not easy to palpate from the surface. The muscle does have superficial parts found at its lateral border and distally.
Even though it is located deep in the upper arm, the brachialis muscle still contributes indirectly to the surface anatomy as its large belly makes the biceps brachii look much larger on the surface than it actually is. You know how the old saying goes, “Behind every great biceps brachii is a great brachialis,” or something like that.
The brachialis originates at the distal half of the anterior side of the humerus. In addition, the origin tendon attaches to the medial and lateral intermuscular septa of the arm, two dividing membranes separating the flexor from the extensor muscles.
Distally, the muscle inserts at the tuberosity of the ulna, where its fibers are also connected to the joint capsule.
The nerve supply for the brachialis comes from the musculocutaneous nerve. However, in 70% to 80% of people, the muscle has double innervation with the radial nerve.
The brachialis is the strongest flexor of the elbow joint, stronger even than the biceps brachii because it is closer to the joint access, and furthermore, only stretches over one joint. A small contraction of the muscle consequently leads to a larger flexion in the elbow.
Another function of the brachialis is helping with maintenance of tension found on the joint capsule, and as a result, working to prevent damages to the capsule during hyper extension.