📖 Read-only demo. All content is browsable; accounts, saved progress, and quizzes need the full app — run it locally from GitHub.

Skip to content
beginnerSource-checked14 min read

The Shoulder: An Overview

The bones, joints, and big picture of how the shoulder trades stability for mobility.

Before this: Fundamental Movement Terms

You will be able to

  • Name the three bones of the shoulder.
  • Describe the main shoulder joints and their types.
  • Explain the trade-off between mobility and stability.
Simplified front view of the right shoulder showing the clavicle, scapula, and humerus, with the deltoid muscle shaded as a cap over the shoulder joint.
Shoulder region — bones and the deltoid (simplified). A beginner-level schematic of the shoulder's three bones and the location of the deltoid over the glenohumeral joint.
Illustration: Anatomy Learning Platform (original) · CC0-1.0 (public domain dedication)

⚠ Safety note

The shoulder's large range of motion comes with less inherent stability. Persistent shoulder pain, weakness, numbness, or a feeling of instability should be checked by a qualified healthcare professional — a trainer does not diagnose or treat these.

Three bones

The shoulder is built from three bones:

  • Clavicle (collarbone) — connects the arm skeleton to the breastbone at the front.
  • Scapula (shoulder blade) — a flat triangular bone on the upper back with a shallow socket.
  • Humerus (upper arm bone) — its rounded head sits in the scapula's socket.

Several joints, working together

The shoulder is not one joint but a complex of several:

  • Glenohumeral joint — the main ball-and-socket joint between the humerus and the scapula's shallow socket. This is what most people mean by "the shoulder joint."
  • Acromioclavicular (AC) joint — between the scapula and clavicle.
  • Sternoclavicular (SC) joint — the only bony link between the arm skeleton and the trunk.
  • Scapulothoracic articulation — the shoulder blade gliding over the rib cage (a functional joint, not a true one).

Mobility vs. stability

The glenohumeral socket is shallow, like a golf ball on a tee. This lets the arm move in almost every direction — but it also means the joint relies heavily on muscles (especially the rotator cuff) for stability, rather than on deep bony fit. This trade-off is the key idea for understanding shoulder training and shoulder injuries.

Sources for this lesson

“Joints are where two bones meet and allow movement; muscles and connective tissue support them.”

Anatomy (MedlinePlus) — U.S. National Library of Medicine (NIH) · Bones, Joints and Muscles overview

Government / official guideline · License: Public domain (U.S. government work); some linked images may be third-party. · Last checked 2026-07-19

“The pectoral girdle (clavicle and scapula) attaches the upper limb to the axial skeleton; the glenohumeral joint is a ball-and-socket joint with a shallow glenoid cavity, giving high mobility and lower stability.”

Anatomy and Physiology 2e — OpenStax, Rice University · Ch. 8.2 The Pectoral Girdle; Ch. 9.4 Synovial Joints

Peer-reviewed textbook · License: CC BY-NC-SA 4.0 · Last checked 2026-07-19

Take the quiz (2 questions)Explore the Shoulder

Sign in to mark this complete, bookmark it, and save private notes.