Hey everyone! This is Matt from Kenhub, and in this tutorial, we will discuss the origin, insertion, innervations, and function of the coracobrachialis, which is a long, slender muscle of the shoulder joint.
The coracobrachialis gets its name from its origin, the coracoids process of the scapula, where its tendon is partly blended with the short head of the biceps.
The insertion of this muscle occurs at the medial surface of the humeral shaft which is between the brachial muscle and the medial head of the triceps. Both the coracobrachialis and the humerus form the lateral border of the axilla where it is the easiest to palpate the muscle.
The nervous supply comes from the musculocutaneous nerve, a branch from the lateral cord of the brachial plexus. This nerve penetrates the coracobrachialis on a middle level.
The contraction of the coracobrachialis leads to two movements at the shoulder joint. On one hand, it bends the arm, known as flexion, and on the other hand, it pulls the arm towards the trunk, which is known as adduction.
To a smaller extent, it also turns the humerus inwards, which is known as inward rotation. When you rotate your arm inward, you find that, with your arm extended, you can turn it farther than you can when your arm is flexed and your arm blocked from over-rotation.
Another important function of the coracobrachialis is the stabilization of the humeral head within the shoulder joint, especially when the arm is hanging freely straight down.