Human Shoulder Anatomy and Physiology


There are 3 bones in the human shoulder, or glenohumeral joint; the humerus, the clavicle, and the scapula. These bones are stabilized by 15+ muscles, depending on how you count them. These muscles function to stabilize the joint. This is what allows you to type, swing, and grasp with utter precision. Homo sapiens shoulder is precisely mobile, but lacks the stability and strength of our great ape cousins.

Gray's Shoulder Joint Depiction
Gray’s Anatomy

The muscles and bones of the shoulder joint work very closely together. They are very often depicted together in anatomy books because of how they functional in unison. The human shoulder joint is nothing short of incredible as a feat of natural evolution. It is a major evolutionary advantage over our primate cousins. Human beings the ability to climb, sprint, and perhaps most incredibly to throw objects accurately over large distances in conjunction with the excellent eye-sight of homo-sapiens sapiens because of our shoulders. And we can still climb, but must use our legs dominantly.

The Clavicle and Scapula are both considered to be part of the shoulder girdle, the structure that supports the appendages of the upper body. The shoulder provides stability for the neck, or upper third of the spine.

Bones of the Shoulder

Scapula – wing bone, or blade bone connects the humerus and clavicle and lies on the back of the rib cage. The name derives from early Roman times when it was thought that the bone resembled a trowel or small shovel.


Humerus – the humerus is a long bone of the shoulder joint, connecting the shoulder girdle to the forearm.

Clavicle – also known as the ‘collarbone’, it is the first bone to ossify in an embryo, and connects the sternum to the scapula. It rotates upon its axis like a key when the shoulder is abducted. It is also the most commonly fractured bone.

Tendons and Ligaments of the Shoulder and Armpit

Gray's Shoulder Tendons

The Glenoid cavity is a shallow depression in the scapula, that connects to the head of the humerus and allows for the arm-bone’s articulation, forms the basis for the ball and socket joint and is held in place by the head of the biceps tendon. The rotator cuff also reinforces this joint with the supraspinatus tendon.

The Rotator Cuff consists of four primary tendons: the supraspinatus muscle, the infraspinatus muscle, the teres minor, and the subscapularis muscle. The tendons of these fours muscles merge to form the rotator cuff tendon.

Gray's Rotator Cuff Ligaments

The Coracoacromial ligament connects the coracoid process (the hook like structure on the shoulder blade) and the acromion (the highest profusion of the shoulder blade). This ligaments helps to shield the head of the humerus.

The AC Joint, or Acromioclavicular joint is the joint at the top of the shoulder that connects the acromion to the the collar-bones. There are several acromioclavicular ligaments as you can see in the image on the right and they are organized to provide added stability to the joint and to house the bursa and synovial fluid that allows the joint to articulate easily.

The conoid ligament connects the clavicle and the coracoid process further stabilizing the collar bone to the shoulder blade.

The caracohumeral ligament connects the coracoid process to the humerus.

Together, these ligaments stabilize and support the shoulder joint, allowing for the extreme mobility that we humans enjoy. However, the large amount of smaller ligaments and tendons sacrifice a certain amount of stability for this increased mobility and range of motion.

Shoulder Muscles

  1. Deltoid – responsible for lifting the arm and giving the shoulder its range of motion. Often this muscle is separated into 3 sub-muscles, anterior, lateral, and posterior as they are able to innervate separately.
  2. Teres Major – A small muscle that runs along the lateral border of the scapula and connect to the humerus.
  3. Teres Minor – extends laterally and obliquely from the head of the humerus to the scapula, underneath the Teres Major. This rotator cuff muscles rotates the head of the humerus and stabilized it as it moves in space.
  4. Supraspinatus – connects the scapula to the humerus and abducts the shoulder and arm.
  5. Infraspinatus – connects from the medial side of the scapula to the humerus to aid in stabilizing the shoulder. A thick layer of muscle on the outside of the shoulder blade and is the main external rotator of the shoulder.
  6. Subscapularis – Directly opposes the infraspinatus muscle on the interior of the shoulder blade. It rotates the humerus medially and adducts it, preventing the displacement of the humerus during motion.
  7. Serratus Anterior – originates on ribs one through eight and connects to the medial interior edge of the scapula. The serratus anterior muscles work in conjunction with the latissimus dorsi to lift the shoulder blades and pull them forward and are one of the primary core support structures for the shoulder. Shoulder injuries often occur in yoga because this muscle is not fully contracted, especially in Chaturanga.
  8. Subclavicus – A small muscles that lies between the clavicle and the first rib that draws the shoulders down and forward.
  9. Pectoralis Minor – a thin and flat muscle in the upper torso that lies underneath the pectorals major and originates in the second, third, and fourth ribs. (sometimes the 5th rib instead of the 4th). This is the primary chest muscle that assists in lifting the shoulders.
  10. Sternocleidomastoid – the primary visible neck muscle that rotates and turns the head and neck. It inserts at the sternum and clavicle and travels up to the mastoid at the temporal lobe of the skull.
  11. Levator Scapulae – the main function of this muscle is to lift the scapula, originates in the neck C1-C4 and travels down to the medial border of the scapula. Works in a state of near unison with the serratus anterior muscles.
  12. Rhomboid Major – connects the shoulder blade to T2-T5 of the mid spine. It is slightly deeper than the trapezius and slightly inferior to the rhomboid minor. Together with the serratus anterior and pectorals minor, it connects the shoulder blades to the rib cage.
  13. Rhomboid Minor – Also connects scapula to the spinal vertebrae, but superior (higher) than the rhomboid major and slightly smaller. Connects C7 and T1 to the shoulder blades. Oftentimes this muscle is completely fused with the Rhomboid major.
  14. Trapezius – a large paired surface muscle in the shape of a diamond, connecting the occipital lobe to the shoulder blades and travels down to the lower thoracic vertebrae. It helps to move the scapula and the arm. Because it connects both the spine and the shoulder blades, this muscle can be one of the primary causes of neck tension in the body.
  15. Latissimus Dorsi – a large flat muscle one the back that originates in the mid and lower back and travels all the way up to the head of the humerus. Is it the largest muscle in the upper body and is implicated for cardiac support and is also an accessory breathing muscle. Tightness in this muscle has been shown to be a primary contributor to back pain.

Nerves of the Shoulder Joint

Gray's Brachial Plexus

The Brachial Plexus is a network of nerve tissue that supplies the arm and shoulder with innervation. Branches of the plexus, in particular from C5-C6, supply the majority of the muscles of the shoulder. The plexus continues down the arm to form the radial, ulnar, and median nerves of the arm.

Blood Vessels of the Shoulder

The blood Vessels of the shoulder function very similarly to the nerves (often in the body, nerves and blood vessels run in parallel to make the innervation of the muscle tissue more accessible to the nervous system. The Auxiliary artery becomes the brachial artery at the upper arm and continues down the arm to become the radial and ulnar arteries. Most of the blood vessels of the shoulder branch off the auxiliary artery.

Rotation in the Shoulder

BursaShoulder bursitis is a common cause of shoulder pain and occurs when the rotator cuff tendons are impinged, or unable to articulate properly. The shoulder bursa is extremely important as it creates smooth range of motion for the arm and shoulder to travel.

Rotator Cuff – the rotator cuff tears are another common cause of shoulder pain, usually cause by a tear in the supraspinatus muscle.

Range of Motion – As I discussed earlier, the shoulder’s range of motion is largely allowed for by the tremendous amount of ligaments, tendons, and muscles that work together to mobilize the arm. This comes at the sacrifice of stability. The stability of the shoulder comes from the muscle tissue, which can limit the range of motion in the shoulder, which may be healthy for the skeleton, especially under large amount of duress. It is easy to see this limited range of motion in body builders, whose muscles have gotten large enough to impede the motion of the shoulder. An appropriate balance between stability and flexibility is what we are looking for in yoga (or at least I am looking for this balance) so that the joint can have maximum longevity.

All References from

Shoulder Anatomy and Physiology

Radial Nerve

Human Shoulder Anatomy

Understanding shoulder anatomy can help to avoid injury, promote rehabilitation, and can assist you in using the joint optimally. Please let me know if you have questions about this article in the comments section at the bottom of the page.shoulder anatomy overall

The human shoulder is a powerful and large anatomical structure. The hinging ball and socket joint allows for vast gains in momentum over short periods of time and is relatively versatile. The shoulder anatomy allows for many types of throwing, fine motor movement down to typing, powerful grasping, hefting objects, climbing, combat, quadruped movement, etc. The shoulder also has a large range of motion; however, this makes the shoulder prone to injury.


Bones of the Shoulder

The shoulder joint is relatively loose. There are three main bones of the shoulder: the collarbone, shoulder-shoulder anatomy bonesblade, and the upper arm bone. These are known as the clavicles, scapula, and humerus, respectively. The shoulder blade also has a bone called the caracoid process which connects to the biceps at the front of the arm and an upwardly angled bone called the acromion that connects to the Clavicle (collarbone) via the CA ligament.

Ligaments of the Shoulder

There are large amounts of ligaments and tendons in the shoulder joint, because of its versatility, stability, and strength. As you can see, the three bones of the joint are combined together with vast arrays and webbings of ligaments that allow for the large range of motion while keep the joint stable. Honestly, the joint is so complex that using words to describe it become somewhat useless. So here’s a huge blown up picture for you to look at in awe of how fucking amazing your shoulders are:


Muscles of the Shoulder

All of the deep ligaments that you see above are supported by muscles tissue. The muscles that make up the rotator cuff are the infraspinatus, shoulder anatomy musclessupraspinatus, subscapularis, and teres. There are also three deltoid muscles on the head of the humerus, the rhomboids that connect the shoulder to the spine and the traps which connect the shoulder and neck, and provide support for the shoulder blades.

The infraspinatus muscle runs along the scapula (shoulder blade), covering the back of it over the teres minor muscle. The teres minor connects the outer arm with the outer lower edge of the shoulder blade. The supraspinatus connects the head of the humerus (arm bone) to the inside edge of the scapula articulating underneath the clavicle (collarbone). The teres major connects the outer clavicle with the back of the humerus; it is more superficial and larger than the teres minor. The subscapularis muscles run on the inside of the shoulder blade, but is not connected to the rib cage which is part of what allows the shoulder blade to have such a broad range of motion. Over all of these muscles are the deltoids, which are the most superficial shoulder muscles. They are separated into anterior, lateral, and posterior sections.

Nerves of the Shoulder

The nerves of the shoulder are also complex; consider that the fine motor function of typing must travel from your spine to your fingertips through the intricacies of the shoulder joint. You also have a very responsive feedback loop between your eyes and hands, which travels within the shoulder and into the forearms and fingers.

There are three primary nerves in the arm that run through the interior of the joint and connect to the digits (fingers).

The radial nerve provides innervation to the dorsal muscles of the arm: triceps, extrinsic extensors of the hands, as well as sensory innervation to the back of the hand, except for the pinky and half of the ring shoulder anatomy nervesfinger. It originates from the brachial plexus, carrying fibers from the ventral roots of spinal nerves C5, C6, C7, C8 & T1.

The ulnar nerve provides innervation to the back of the other three fingers, including the thumb. It also provides the majority of the innervation of the forearm and head of the bicep. The ulnar nerve originates from the C8T1 nerve roots (and occasionally carries C7 fibers) which form part of the medial cord of the brachial plexus, and descends on the posteromedial aspect of the humerus.

The medial nerve provides innervation for the inside of the thumb, pointer, middle, and half of the ring finger. It also innervates the lateral and inferior portions of the forearm. The median nerve originates from the lateral and medial cords of the brachial plexus, and has contributions from ventral roots of C5-C7(lateral cord) and C8 & T1 (medial cord).

Here is a final picture of the brachial plexus to assist in visualizing how the nerves flow down the arms.




This concludes my article on shoulder anatomy; please write any questions below!