The coracobrachialis is a small, cylindrical muscle located in the upper arm. It is one of the muscles that make up the anterior compartment of the arm, playing a role in stabilizing the shoulder joint. This muscle extends from the scapula to the humerus, assisting in various shoulder and arm movements.
Location
The coracobrachialis is located in the upper part of the arm. It originates from the coracoid process of the scapula, a small hook-like structure near the shoulder joint. From there, it extends downwards, inserting into the medial side of the humerus shaft, between the brachialis and biceps brachii muscles.
Anatomy
The coracobrachialis muscle is an essential component of the upper arm with specific anatomical characteristics that allow it to function effectively in arm movement and stabilization.
Origin
The coracobrachialis originates from the coracoid process of the scapula, which is a small, hook-like structure projecting from the upper part of the scapula near the shoulder joint. It shares this origin point with the short head of the biceps brachii muscle.
Insertion
The muscle extends diagonally downward and laterally from its origin to insert into the medial surface of the mid-shaft of the humerus. This insertion is typically located on the rough area of the bone known as the medial supracondylar ridge, which is situated between the triceps brachii insertion and the insertion of the biceps brachii.
Structure
The coracobrachialis is a relatively small, elongated muscle. It starts with a tendonous beginning at the coracoid process and then continues as a cylindrical, fleshy muscle belly before narrowing into a tendon again at its insertion. It lies deep within the upper arm, situated between the biceps brachii in the front and the triceps brachii at the back.
Blood Supply
The muscular branch of the brachial artery primarily supplies the coracobrachialis. This artery travels along the muscle, providing it with essential nutrients and oxygen.
Innervation
The muscle receives innervation from the musculocutaneous nerve, which originates from the lateral cord of the brachial plexus, with nerve roots from C5 to C7. The nerve enters the muscle on its medial side and provides the necessary signals for muscle contraction and sensation.
Relations
- Anteriorly: The coracobrachialis lies beneath the skin and fascia of the upper arm and is positioned superficially to the brachial artery and the median nerve.
- Posteriorly: It is situated anterior to the short head of the biceps brachii and the triceps brachii muscle.
- Medially: The muscle is related to the axillary artery and vein, and the nerves of the brachial plexus.
Functional Compartment
The coracobrachialis is part of the anterior compartment of the arm along with the biceps brachii and brachialis muscles, contributing to flexion and adduction at the shoulder joint.
Function
The coracobrachialis muscle performs several important functions related to the movement and stabilization of the shoulder:
- Shoulder Flexion: The primary function of the coracobrachialis is to flex the shoulder, which means it helps to bring the arm forward and up towards the body.
- Shoulder Adduction: The muscle also assists in adducting the shoulder, meaning it helps to bring the arm closer to the body from a raised position.
- Shoulder Stabilization: By maintaining tension across the shoulder joint, the coracobrachialis helps stabilize the shoulder, particularly during arm movements, thus protecting the joint from dislocation and injury.
Clinical Significance
Muscle Strains and Injuries: The coracobrachialis can be susceptible to overuse injuries and strains, especially in athletes or individuals engaging in repetitive arm lifting activities. Injuries to this muscle can result in pain and restricted movement in the shoulder.
Neurovascular Entrapment: Due to its proximity to the brachial plexus and major blood vessels, hypertrophy or spasm of the coracobrachialis can contribute to neurovascular compression syndromes, affecting nerve function and blood flow in the arm.
Shoulder Stabilization: Clinically, the coracobrachialis is important for stabilizing the shoulder joint. Weakness or dysfunction in this muscle can lead to improper shoulder mechanics and increase the risk of injuries in other shoulder muscles, including the rotator cuff.
Surgical and Injection Procedures: The coracobrachialis muscle is a landmark for surgical procedures and injections in the shoulder region. Understanding its anatomy is crucial for avoiding complications during these interventions.
Rehabilitation and Physical Therapy: In rehabilitation settings, strengthening and stretching the coracobrachialis are common practices, especially after shoulder injuries or surgeries, to restore function and prevent future injuries.
