Shoulder Part 1

The shoulder girdle is a complex structure that connects the upper limb to the vertebral column, enabling a wide range of movements.

The Trapezius is a large, diamond-shaped muscle that spans the upper back and neck. Its fibers have different functions: upper fibers elevate the scapula, middle fibers retract it, and lower fibers depress it. It also plays a key role in rotating the scapula during arm elevation.

The Latissimus Dorsi is a large, flat muscle that covers the lower back. It works to adduct (pull towards the body), extend, and medially rotate the arm. It also assists in trunk elevation during activities like climbing and swimming.

The Levator Scapulae muscle, located at the back of the neck, helps elevate the scapula alongside the upper fibers of the trapezius.

The Rhomboids (Minor and Major) are deep muscles that help retract the scapula, pulling it towards the spine, and also contribute to downward rotation of the scapula, stabilizing the shoulder joint.

Elevating the shoulder means raising it towards the ear. Depressing the shoulder involves lowering it away from the ear. This movement is achieved primarily by the trapezius and serratus anterior muscles.

Upward rotation of the glenoid cavity involves moving the scapula to a higher position, rotating it upward. Downward rotation brings the scapula back to a lower position. The trapezius and serratus anterior are key in this movement.

Protraction involves pulling the scapula forward, like reaching out with your shoulder. Retraction brings the scapula backward, towards the spine. The pectoralis minor and rhomboids are involved.

The pectoralis major is a large muscle that covers the chest. Its primary function is to adduct (pull towards the body), flex, and medially rotate the arm. It's a big contributor to activities like climbing and rowing.

The Pectoralis Minor is a smaller muscle located beneath the pectoralis major. It protracts the scapula, pulling it forward, and depresses it, pulling it downwards. Additionally, it assists with forced inspiration.

The Serratus Anterior is a muscle on the side of the rib cage. It plays a key role in protracting and rotating the scapula, anchoring it securely to the ribcage. This muscle also assists with respiration.

The deltoid muscle is a rounded muscle that covers the shoulder joint. It performs multiple actions: flexion, extension, medial and lateral rotation, and abduction (lifting the arm to the side).

The Supraspinatus is a small, powerful muscle located above the spine of the scapula. It initiates arm abduction (lifting the arm away from the body) and stabilizes the shoulder joint.

The Infraspinatus is a muscle located below the spine of the scapula. It helps with lateral rotation of the arm (rotating the arm outward) and also ensures stability of the shoulder joint.

The Teres Minor, a small muscle located below the infraspinatus, works with it to laterally rotate the arm and provide stability to the shoulder joint.

The Teres Major is a muscle located below the teres minor. It assists in medial rotation (rotating inward) and adduction (pulling toward the body) of the arm.

The Subscapularis is a muscle located on the front of the scapula. It helps with medial rotation of the arm and works to stabilize the shoulder joint.

The Sternoclavicular joint is a synovial joint that connects the sternum, clavicle, and first costal cartilage. It's crucial for movement and stability of the shoulder girdle.

The Acromioclavicular joint is a synovial joint that connects the acromion of the scapula with the clavicle. It allows for movement and stability of the shoulder.

This ligament connects the clavicle to the first rib, preventing excessive upward movement of the clavicle and providing stability to the Sternoclavicular joint.

Coronoid and trapezoid components of the coracoclavicular ligament, along with the coracoacromial ligament, are essential for stabilizing the Acromioclavicular joint.