The muscles of the arm are primarily divided into compartments within the upper arm and the forearm, each responsible for specific movements of the shoulder, elbow, and wrist.
Overview of Arm Muscle Groups and Functions
1. Upper Arm (Brachium)
The upper arm is divided by intermuscular septa into two main compartments:
- Anterior Compartment (Flexors): This group is primarily responsible for bending the elbow and shoulder and turning the palm upward.
- Biceps Brachii: A two-headed muscle that flexes the elbow, assists in shoulder flexion, and is the primary supinator of the forearm (turning the palm up).
- Brachialis: Located deep to the biceps, it is considered the strongest flexor of the elbow.
- Coracobrachialis: A deep muscle that assists in flexing and adducting the arm at the shoulder joint.
- Posterior Compartment (Extensors): This group is responsible for straightening the arm.
- Triceps Brachii: A three-headed muscle (long, lateral, and medial heads) that serves as the principal extensor of the elbow. The long head also assists in stabilizing the shoulder joint and extending the arm at the shoulder.
- Anconeus: A small triangular muscle at the elbow that assists the triceps in extension and stabilizes the ulna during movement.
2. Forearm (Antebrachium)
The forearm contains numerous muscles that manage complex movements of the wrist and fingers.
- Anterior Forearm (Flexors/Pronators): These muscles, located on the underside of the forearm, flex the wrist and fingers and pronate the forearm (turn the palm down). Key muscles include the flexor carpi radialis, flexor carpi ulnaris, and pronator teres.
- Posterior Forearm (Extensors/Supinators): Located on the top of the forearm, these muscles extend the wrist and fingers and supinate the forearm.
- Brachioradialis: Although located in the forearm, it primarily acts to flex the elbow, especially when the forearm is in a neutral position.
- Supinator: A deep muscle responsible for turning the palm upward.