What are Joints and Articulations?
A joint, or articulation, is any point where two or more bones meet. Joints are classified by the tissue that connects the bones (structural) and by how much movement they allow (functional).
Joints are connections between bones classified structurally as fibrous, cartilaginous, or synovial, and functionally as immovable (synarthrosis), slightly movable (amphiarthrosis), or freely movable (diarthrosis).
- •Have a fluid-filled joint capsule
- •Articular cartilage cushions bone ends
- •Freely movable (diarthroses) — e.g. knee, shoulder
- •Bones joined by fibrous tissue or cartilage, no joint cavity
- •Little to no movement
- •Immovable or slightly movable — e.g. skull sutures, pubic symphysis
Step-by-step worked examples
Classify the knee joint structurally and functionally.
Structurally, the knee has a fluid-filled joint capsule and articular cartilage, so it is a synovial joint Functionally, it allows a large range of motion (flexion/extension) Therefore the knee is a synovial, diarthrotic (freely movable) hinge joint
Classify a skull suture, such as the coronal suture.
Structurally, adjacent skull bones are joined by dense fibrous connective tissue, so it is a fibrous joint Functionally, sutures allow essentially no movement in the adult skull Therefore a suture is a fibrous, synarthrotic (immovable) joint
The pubic symphysis widens slightly during childbirth. How is it classified?
Structurally, the two pubic bones are joined by fibrocartilage, so it is a cartilaginous joint Functionally, it permits only slight movement, more so during late pregnancy under hormonal influence Therefore the pubic symphysis is a cartilaginous, amphiarthrotic (slightly movable) joint
Flashcards
Quick quiz
Q1.Which structural joint type has a fluid-filled cavity?
Q2.What functional category describes an immovable joint?
Q3.Which of these is a cartilaginous joint?
Q4.The knee joint is best classified as which functional type?
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Common mistakes
Assuming 'joint' always means a freely moving structure. — Correct: Immovable connections, like skull sutures, are joints too — just synarthroses.
Confusing structural and functional classification as the same thing. — Correct: Structural classification is about the connecting tissue; functional classification is about the amount of movement allowed.
Thinking all cartilaginous joints move freely. — Correct: Cartilaginous joints like the pubic symphysis only allow slight movement (amphiarthrosis).
Believing synovial fluid is found in all joints. — Correct: Synovial fluid is only present in synovial joints, not in fibrous or cartilaginous ones.
FAQ
What are joints and articulations?
They are the points where bones meet, classified by connecting tissue (fibrous, cartilaginous, synovial) and by movement allowed.
What is the difference between synarthrosis and diarthrosis?
Synarthrosis is an immovable joint (like a suture); diarthrosis is a freely movable joint (like the knee).
What are examples of synovial joints?
The knee, shoulder, hip, and elbow are all synovial joints, each with a fluid-filled capsule.
How are joints classified in anatomy?
By structure (fibrous, cartilaginous, synovial) and by function (synarthrosis, amphiarthrosis, diarthrosis).