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Anatomy & Physiology (Open + Free)
Sy lla bu s
Unit 4:: Skeletal System
Introduction
Module 11 /
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Mor e
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Skeletal Structures and
Functions
Skeletal Lev els of
Organization
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Articulations: Diarthrosis
Describe the functional
classification of articulations,
based on degree of m ov em ent
allowed—sy narthrotic,
am phiarthrotic, and diarthrotic
—and prov ide exam ples of each
ty pe.
The articulations that people are most familiar with are
diarthrosis articulations, which have wide
ranges of motion. Diarthrotic articulations are said to be freely moveable and have a joint cavity. A joint
cavity is a structure that consists of a joint capsule which surrounds the joint, and a synovial membrane which
is inside the joint and produces a fluid known as synovial fluid. These joints are known as synovial joints and
are further classified according to the type of movement allowed at the joint.
Nonaxial Joints
Nonaxial joints do not have a pivot or axis of movement. An example are gliding joints, also known as plane
joints. These joints do not allow much movement other than sliding and twisting. These are often found in
certain articulations in the wrist and ankle.
Gliding joint of the wrist
Uniaxial or Monoaxial Joints
These joints have one axis of movement and are more moveable than gliding joints. Examples of uniaxial
joints are hinge and pivot joints.
These joints have protrusions that fit into a corresponding depression; hinge joints, such as the elbow, allow
the movement of flexion and extension. The pivot joint of the atlanto-axial joint (the atlas or C-1 on the axis
or C-2) rotation of the head and neck. For example, when you shake your head "no" you are using this joint to
rotate your head.
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Elbow joint
Cross section of v ertabra
Biaxial Joints
Biaxial joints have two axes of movement and therefore allow more movements than uniaxial joints. One
example of a biaxial joint are saddle joints, such as the thumb. These joints were appropriately named
because they look like saddles; there are two curved surfaces that meet and allow limited motion in many
directions.
thum b joint
Another example of a biaxial joint is an ellipsoid or condlyar joint. Ellipsoid articulations, also called condyloid
articulations, have oddly shaped or elliptical interactions that articulate to allow movement in two planes with
no rotation. These are present in the fingers and toes.
Finger joints
Triaxial Joints
As you can guess, triaxial joints are the most moveable with three axes of movement. The ball and socket
joints such as the shoulder and hip, have the widest range of motion. They are aptly named as the head of the
bone resembles a "ball" and the articulating bone of the joint (either the scapula or coxal bone) has a deep pit
for the "socket".
Hip joint