Muscles that Move the Shoulder and Upper Limb

Overview of Upper Limb Muscles

The muscles of the upper limb are responsible for the movement of the shoulder, elbow, and wrist. These muscles originate from the somatic mesoderm of the limb buds during embryonic development and are organized into functional groups based on their location and innervation.

• Shoulder movement: Muscles must attach to the humerus to move the shoulder.

• Elbow movement: Muscles must attach to the ulna or radius to move the elbow.

• Ventral muscles: These are flexors, innervated by the musculocutaneous, median, or ulnar nerves.

• Dorsal muscles: These are extensors, innervated by the radial nerve.

• The axillary nerve innervates specific muscles of the shoulder.

Additional info: The brachial plexus is the network of nerves that supplies the upper limb, dividing into five major nerves: musculocutaneous, axillary, radial, median, and ulnar.

Brachial Plexus Organization

The brachial plexus is a complex network of nerves that provides motor and sensory innervation to the upper limb. It is organized as follows:

• 5 Nerves

• 3 Cords

• 6 Divisions

• 3 Trunks

Dorsal (posterior) divisions: Elevators/extensors (axillary and radial nerves) Ventral (anterior) divisions: Depressors/flexors (musculocutaneous, median, and ulnar nerves)

Muscles that Move the Humerus

Coracobrachialis

The coracobrachialis is a muscle of the upper arm that acts on the shoulder joint.

• Origin: Coracoid process of the scapula

• Insertion: Humerus, distal to the tuberosity

• Innervation: Musculocutaneous nerve

• Functions: Flexes and adducts the shoulder

• Does not cross the elbow joint

Example: The coracobrachialis is used when bringing the arm forward and toward the body, such as when reaching across the chest.

Muscles that Move the Elbow

Brachialis

The brachialis is a primary flexor of the elbow, located deep to the biceps brachii.

• Origin: Humerus, distal flexor surface

• Insertion: Coronoid process of the ulna

• Innervation: Musculocutaneous nerve

• Function: Flexes the elbow

Example: The brachialis is active during lifting movements, such as performing a bicep curl.

Biceps Brachii

The biceps brachii is a two-headed muscle that acts on both the shoulder and elbow joints.

• Insertion: Radial tuberosity

• Innervation: Musculocutaneous nerve

• Function: Flexes the shoulder and elbow, supinates the forearm

• Short head origin: Coracoid process of the scapula

• Long head origin: Supraglenoid tubercle of the scapula

Example: The biceps brachii is used when turning a doorknob (supination) or lifting objects (elbow flexion).

Additional info: The coracoid process is also the origin for the coracobrachialis and the short head of the biceps brachii.