Articulations Form Where Bones Join Together
LEARNING OBJECTIVES
1.
Describe
the characteristics of fibrous and carti-
laginous joints.
2.
Identify
the structures of synovial joints.
n
articulation
or joint is a point of contact be-
tween bones, between cartilage and bone, or
between teeth and bones. There are two clas-
sification schemes for joints; one is based on
how the bones come together and the other on how the
bones work together to make the body move.
Articulations are Classified
by Structure or Function
An articulation can be classified
functionally based on the range
of movement possible by the joint.
The shape of the bones, the place-
ment of the ligaments, and the
flexibility of tendons are impor-
tant for determining movement
in a joint. There are several func-
tional classifications:
A synarthrosis (
sin'-ar-THRO-sis
) is a very strong,
tightly fitted joint that permits virutally no movement.
The sutures of the skull are an example of this limited-
movement type of articulation.
An amphiarthrosis
(
am'-fe-ar-THRO-sis
)
is
looser
than a synarthrosis and permits some movement.
The joint formed between two vertebrae represents
an amphiarthrosis. The intervertebral disc interferes
with free movement of this joint.
A diarthrosis
(
di'-ar-THRO-sis
)
is even looser and
more freely movable than an amphiarthrosis. Most
articulations of the body are of this type.
The structure of a joint determines its strength and flex-
ibility. Joints can also be classified structurally in one of
three categories: •
Fibrous (
Fl-brus
) joints contain varying densities of
irregular dense collagenous connective tissue (Figure
5.13):
• Sutures, like those that join skull bones, have thin
layers of connective tissue.
3.
List
the types of synovial joints and give exam-
ples of each.
4.
Explain
the various types of joint movements.
• A syndesmosis has more space between the bones
and more connective tissue than a suture. One
example is the joint that forms between the tibia and
fibula distally (distal tibiofibular joint) at the ankle.
Another example is a
gomphosis,
the attachment of a tooth
into its socket.
• Interosseous membranes are large sheets of dense
connective tissue that span greater distances and
connect long bones, such as the ulna and radius.
As their name implies, cartilaginous joints (
kar-ti-
LAJ-i-nus
) are connected by cartilage (see Figure 5.13):
• A synchondrosis (
sin'-kon-DRO-sis
) has hyaline
cartilage and is immovable, like the epiphyseal
plates within long bones.
• In a symphysis (
SIM-fi-sis
), the bones are joined by
a broad, flat disc of fibrocartilage—such as on the
anterior pelvis where the pubic bones articulate—
so they are only slightly movable.
The synovial joints (
si-NO-ve-al
) have numerous
components
and
are
the
most
common
type
of
articulation. These joints are described in more detail
in the next section (Figure 5.13).
Synovial Joints Have
Complex Structures
Synovial joints are structurally more complex than the
other types of joints. They have a fluid-filled cavity be-
tween the bones, and the bones
are covered by articular carti-
lage. A fibrous capsule lined
with
a
synovial
membrane
surrounds the cavity, which is
filled with synovial fluid. The
fluid and cartilage lubricate this freely movable joint.
Synovial joints have ligaments outside and sometimes
within to hold the joints together. Also, some synovial
joints, such as the shoulder and knee, have additional
lubricating sacs called bursae (
BER-se
) between the
skin and bone.
ligaments
(LIG-a-
ments) Dense regular
connective tissue that
attaches bone to bone.
tendons
(TEN-dons)
White fibrous cords of
dense regular connec-
tive tissue that attach
muscles to bones.
articular cartilage
(ar-TIK-D-lar) Hyaline
cartilage attached
to articular bone
surfaces.
136
CHAPTER 5
The Skeletal System
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