The human shoulder is a complex structure that must be stable enough to support the actions of the arm and hands like pulling, lifting, and pushing object. At the same time, it must be mobile enough for these actions to occur. What tendons, joints, muscles, and bones make up the human shoulder?
“Put your shoulder to the wheel.” — Aesop
The shoulder isn’t just one bone, it’s actually made up of three different bones and various tendons, ligaments, and muscles. The three bones located in the shoulder are the humerus, the scapula, and the clavicle. Beyond this, there is also a shoulder joint arrayed in a ball and socket formation, a rotator cuff, and various muscles like the deltoid muscle and the teres major muscle. Let’s examine the various bones, muscles, and joints that make up the shoulder more closely.
Before we proceed any further, let’s define some of the terms that will be used in the discussion of the shoulder.
- Bones – Though many people don’t usually think of bones as organs, bones are in fact organs. They are just rigid organs that function to maintain and support the shape of the body by comprising the skeleton, store minerals, and – in conjunction with the muscles – enable the mobility of the body.
- Tendons – Tendons are also sometimes referred to as sinew, and they are portions of connective tissue. Tendons are made of fibrous tissue, and they usually join muscle to bone. Tendons are made out of parallel portions of collagen fibers packed closely together, and these collagen fibers transmit various forces through groups of muscle and bone. The elastic property of tendons helps modulate forces during motion.
- Ligaments – While tendons are connective tissues that join bones to muscles, ligaments are connective tissues that join bones to other bones. Much like tendons, ligaments are made out of fibrous connective tissue composed of collagen fibers. Some ligaments function to prevent certain movements or otherwise limit mobility.
- Muscles – Muscles are soft tissues made out of muscle cells capable of sliding past each other. Muscle cells can both contract and expand, and they take advantage of this ability to produce motion. Muscle cells are responsible for changing the position of the body, maintaining body position, movements, and the operation of internal organs like heart contractions.
Format of the Shoulder
The shoulder is made out of a ball and socket joint created by the scapula, humerus, and the muscles, ligaments, and tendons that support those bones. These supporting tissues are all attached to the scapula, humerus, and clavicle. The shoulder joint is located between the glenoid fossa of the scapula and the humerus. While the shoulder joint is the main joint in the cellar, the sternoclavicular joint and the acromioclavicular joint are also important in the movement of the shoulder. On the end of the bones within the shoulder, there is cartilage that allows the bones to easily move past one another. Finally, around the joint space are muscles such as the rotator cuff. These muscles give stability to the shoulder and arm and assist in movement.
The Shoulder Joint
Though there are other joints in the shoulder, the shoulder joint functions as the primary joint in the shoulder. The shoulder joint is a ball and socket joint like a hinge, meaning that it lets the arm rotate in a circular manner, in addition to letting the arm move like a hinge outwards or upwards. One end of the humerus, the medial anterior surface, serves as the ball of the ball and socket joint. Meanwhile, the socket of the joint is comprised of the glenoid cavity, a region of the lateral scapula.
Fibrous cartilage, articular cartilage, and synovial membranes join the humerus to the scapula. These connections are fairly weak and loose, which allows the arm to have much more mobility than other joints in the body. This also means that the shoulder joint is easier to dislocate than many other joints.
“If I have seen further than others, it is by standing upon the shoulders of giants.” — Isaac Newton
The glenohumeral joint is a collection of soft tissue that attaches to the humerus, scapula, and part of the bicep. The synovial membrane lines this tissue, and a ligament referred to as the coracohumeral ligament joins the humerus and scapula together. Three other ligaments also attach the humerus and scapula, with all the ligaments together dubbed the glenohumeral ligaments.
The flexion of the shoulder joint is done through the deltoid’s anterior fibers, as well as the pectoralis major and coracobrachialis. The extension of the shoulder joint is carried out through the movement of the deltoid’s posterior fibers and the latissimus dorsi. The abduction of the shoulder’s frontal plane are handled by the supraspinatus, the deltoid, the trapezius and the serratus anterior. Meanwhile, adduction of the shoulder is handled by the teres major, the subscapularis, the latissimus dorsi, and the pectoralis major.
The capsule of the shoulder joint can become inflamed, which restricts movement and causes pain. This condition is frequently referred to as adhesive capsulitis or frozen shoulder. Superior labrum anterior to posterior (SLAP) tears are when the glenoid labrum is ruptured and they usually cause pain when the arm is in a certain position or lifted at a certain angle. SLAP tears frequently necessitate surgery.
The Rotator Cuff
Though commonly thought of as a single muscle, the rotator cuff is actually a group of four muscles along with their supporting tendons which stabilize the shoulder during movement. The four muscles that comprise the rotator cuff are the subscapularis, supraspinatus, teres minor, and the infraspinatus. They function together to hold the head of the humerus within the glenoid cavity, by attaching to the head of the humerus and adhering to the glenohumeral capsule.
This is necessary because otherwise, the humeral head would move up words when pulled by the deltoid muscle as the arm starts to rise. However, the head/glenoid end of the humerus is kept within the glenoid cavity thanks to the rotator cuff. The external rotation of the arm is handled primarily by the teres minor muscle, as well as the infraspinatus muscle and portions of the deltoid muscle.
The four muscles have tendons which link together to form the rotator cuff tendon. The rotator cuff tendon, the coracohumeral ligament, the glenohumeral ligament, and the articular capsule are joined together in a sheet of muscle.
Damage to the rotator cuff leads to difficulty moving the arm and pain. Rotator cuff injuries frequently manifest due to repetitive stress injuries, repeated overhead motions or repeated pulling motions. Athletes that frequently move their arms above their heads are more likely than the average person to experience a rotator cuff tear. Rotator cuff tears can be treated by physical therapy, rest, ice, and potentially surgery if these previous methods of treatment have proved unsuccessful.
Minor Muscles Of The Shoulder
There are other muscles within the shoulder region in addition to the muscles that compose the rotator cuff, such as the teres major muscle and deltoid muscle, which support the actions of the rotator cuff. The teres major muscle is found attached to the outer surface of the rear of the scapula, fitted just underneath the teres minor muscle. The deltoid muscle envelops the shoulder joint across three different sides, and the muscle is located near the scapula, the acromion, and the upper third of the clavicle. The deltoid muscle group assists in various movements of the shoulder such as flexing and extending, while the teres major assists with the rotation of the humerus.
“I like a woman with a head on her shoulders. I hate necks.” — Steve Martin
Muscles found at the front of the chest and associated with the movement of the shoulder include the subclavias, the levator scapulae, the pectoralis minor, the serratus anterior, and the sternocleidomastoid. Muscles found in the back of the chest associated with the movement of the shoulder include the Latissimus dorsi, the Levator scapulae, the trapezius, and the rhomboid major and rhomboid minor.
Recapping: Ligaments, Bones, Tendons In The Shoulder
Ligaments found in the shoulder include: the superior, middle and inferior glenohumeral ligaments. The coracohumeral ligament, the transverse humeral ligament, the coraco-clavicular ligament.
Bones of the shoulder: The scapule, the clavicle, and the humerus.
Tendons of the shoulder: The rotator cuff is made up of four muscles – infraspinatus, supraspinatus, subscapularis, and teres minor. Each of these muscles has its own tendons that support the humerus. The upper portion of the bicep also has a tendon that attaches it to the bones within the shoulder.
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