Upper Body Muscles

Muscles of Upper Extremity: Shoulder & Arms

The muscles that form the shoulder girdle are the pectoralis major, pectoralis minor, the deltoids, trapezius, and the serratus anterior.
The scapula forms the posterior of the shoulder girdle.The intrinsic muscles of the scapula are the supraspinatus, infraspinatus, teres minor, and subscapularis. Together they are called the Rotator Calf Muscles.

The shoulder muscles provide the highest range of motion compared to any joint in the body. But with larger range of motion, the shoulder is more prone to instability and injury.

Trapezius :

is a wide muscle that extends along the back of the neck and shoulders and is trapezoid in shape. It is responsible for elevating the shoulder blade and rotating it during arm abduction.

Deltoid:

is a large triangular muscle that covers the glenohumeral joint, where the upper arm inserts into the shoulder socket. It is responsible for flexion and medial rotation of the arm. It's also responsible for arm abduction, extension, and lateral rotation.

Teres Major & Teres Minor:

The main function of teres major muscle is to produce movements of the humerus on the shoulder joint. By contracting, it causes extension and movement of the humerus posteriorly. It also causes rotation of the arm medially towards the trunk (internal rotation). Both teres major and teres minor help to the stabilization of the shoulder joint.

The main function of teres minor muscle is to stabilizes the ball-and-socket glenohumeral joint by holding the humeral head into the shallow glenoid cavity of the scapula (socket). The teres minor also laterally or externally rotates the arm at the shoulder joint.

Rhomboid:

is a flat trapezoid muscle in the back that reaches from the second, third, fourth, and fifth vertebrae to the shoulder blade. It is a deeper muscle of the shoulder

Muscles of the Arm:

The main muscles of the arm are

Biceps brachii
Brachialis
Brachioradialis
Triceps brachii

Biceps Brachii :

This muscle contains two heads ( long and short) that originate at the front and back of the shoulder and join together at the elbow. Flexion at the elbow brings the forearm toward the upper arm. The two heads near the shoulder help with flexion and adduction of the upper arm.

Origin: Long head originates from the supraglenoid tubercle of the scapula.
Origin: Short head originates from the coracoid process of the scapula.
Insertion: Both the heads insert distally into the radial tuberosity and the fascia of the forearm.

Detailed Muscle Structure of the Arm

Brachioradialis :

Origin: lateral supracondylar ridge of humerus
Insertion: distally at the base of the styloid process of radius

Brachialis :

This muscle lies underneath the biceps. It acts as a bridge between your humerus and ulna. It helps in the flexion movement of the forearm.The brachialis is an elbow flexor that originates from the distal anterior humerus and inserts onto the ulnar tuberosity.

Triceps Brachii :

The triceps muscle, runs along the back of the humerus and allows for the flexion and extension of your forearm. It also helps to stabilize your shoulder joint.

Origin:
Long head originates from the infraglenoid tubercle of the scapula. Lateral and medial heads originate from the humerus.
Insertion:
Distally, the heads connect into one tendon which inserts onto the olecranon of the ulna.

Coracobrachialis :

This muscle is located near the shoulder. It allows adduction of your upper arm and flexion of your shoulder. It also helps to stabilize your humerus within your shoulder joint.

Conclusion

Muscles, tendons, and ligaments work together to keep the arm bone in the shoulder socket. They also protect the main shoulder, the glenohumeral joint. About eight shoulder muscles attach to the shoulder blade (scapula), upper arm (humerus), and collar bone (clavicle). Many other muscles play a part in stabilizing and guiding the shoulder and its movements.

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