Brachialis And Coracobrachialis Muscles
We can turn our arms and place our hands in a multitude of positions. All of the muscles that move our arms collectively make that possible. Among all the arm muscles, you’re probably already somewhat familiar with the biceps and triceps. But, have you heard of brachialis and coracobrachialis? In this article, we’ll take a closer look at two additional arm flexors, the brachialis and coracobrachialis. Read on to find out what important movements we need these muscles to do.
Location: The other anterior arm muscles
Brachialis and coracobrachialis are found in the anterior compartment of the arm along with biceps brachii, which I wrote about previously. The anterior compartment includes the group of muscles on the front of the arm. Coracobrachialis is on the medial side of this group. The attachment of its proximal tendon is superficial to (on top of) the tendon of the short head of the biceps brachii. It then runs medial to brachialis and biceps brachii. Brachialis is deeper inside this group of muscles in the anterior compartment of the arm. It’s deep to the biceps brachii.
Muscle attachments
When we talk about muscle attachments, it’s important to remember that anatomy texts and articles that you read report what’s most common. As with many muscles, there is some variation from person to person in the specific muscle attachments for these two muscles. It’s hard to know the extent of that variation, as most of that knowledge comes from cadaver dissection. Specific muscle attachments are often a difficult, and in some cases impossible, thing to see in live humans.
Brachialis
Most commonly, brachialis attaches proximally to the distal anterior humerus. Distally, it generally attaches to the coronoid process and the ulnar tuberosity. Researchers have seen variation in the particular structure of this muscle across the population in cadaver dissection. While it’s generally described as having a single muscle belly, in less common variations, it has two muscle bellies.
Coracobrachialis
Generally, the coracobrachialis attaches proximally to the coracoid process of the scapula. Additionally, some researchers report that some fibers merge with the tendon of biceps brachii short head. Distally, this muscle attaches to the shaft of the humerus. More recent studies of coracobrachialis have found that one common variation of this muscle includes two muscle bellies, rather than one, with the more superficial and deep parts of this muscle penetrated by the musculocutaneous nerve (the nerve that innervates this muscle). Other less common variations have three or even four muscle bellies.
Muscle actions
Brachialis
The primary action of the brachialis muscle is flexion of the forearm at the elbow. This is often surprising to people. Many people think it’s the biceps brachii that primarily does this action. While the biceps brachii assists in flexion of the forearm, the brachialis is the primary mover in that action.
Coracobrachialis
The primary action of the coracobrachialis is adduction of the arm at the shoulder joint. Remember that adduction is bringing something closer to the midline. So, adduction of the arm is bringing the arm into the side of the body. Coracobrachialis assists with flexion of the arm at the shoulder. It can also assist in stabilizing the head of the humerus in the shoulder socket.
Conclusion
As with most joints in our body, multiple muscles work together to create movement at the shoulder and elbow joints. Flexion of the forearm at the elbow is primarily initiated by brachialis. Arm adduction is the primary action of coracobrachialis. However, both of these muscles assist with additional actions. Coracobrachialis can assist the biceps brachii with flexion of the arm at the shoulder. Biceps brachii assists brachialis with flexion of the forearm at the elbow.