8
256
UNIT 2
Covering, Support, and Movement of the Body
Check Your Understanding
5.
What are the two layers of the articular capsule?
6.
How do bursae and tendon sheaths improve joint function?
7.
Generally speaking, what factor is most important in
stabilizing synovial joints?
8.
What is the importance of weeping lubrication?
For answers, see Appendix H.
Movements Allowed by Synovial Joints
Name and describe (or perform) the common body
movements.
Name and provide examples of the six types of synovial
joints based on the movement(s) allowed.
Every skeletal muscle of the body is attached to bone or other con-
nective tissue structures at no fewer than two points. Te muscle’s
origin
is attached to the immovable (or less movable) bone. Its
other end, the
insertion
, is attached to the movable bone. Body
movement occurs when muscles contract across joints and their
insertion moves toward their origin. Te movements can be de-
scribed in directional terms relative to the lines, or axes, around
which the body part moves and the planes of space along which
the movement occurs, that is, along the transverse, frontal, or sag-
ittal plane. (See Chapter 1 to review these planes.)
Range of motion allowed by synovial joints varies from
non-
axial movement
(slipping movements only, since there is no
axis around which movement can occur) to
uniaxial move-
ment
(movement in one plane) to
biaxial movement
(move-
ment in two planes) to
multiaxial movement
(movement in or
around all three planes of space and axes). Range of motion var-
ies greatly in different people. In some, such as trained gymnasts
or acrobats, range of joint movement may be extraordinary. Te
ranges of motion at the major joints are given in the far right
column of ±able 8.2.
Tere are three general types of movements:
gliding
,
angular
movements
, and
rotation
. Te most common body movements
allowed by synovial joints are described next and illustrated in
Figure 8.5
.
Gliding Movements
Gliding
occurs when one flat, or nearly flat, bone surface glides or
slips over another (back-and-forth and side-to-side; Figure 8.5a)
without appreciable angulation or rotation. Gliding occurs at the
intercarpal and intertarsal joints, and between the flat articular
processes of the vertebrae (±able 8.2).
Angular Movements
Angular movements
(Figure 8.5b–e) increase or decrease the
angle between two bones. Tese movements may occur in any
plane of the body and include flexion, extension, hyperexten-
sion, abduction, adduction, and circumduction.
Gliding
(a) Gliding movements at the wrist
(b) Angular movements: flexion, extension, and hyperextension of
the neck
Hyperextension
Extension
Flexion
Hyperextension
Flexion
Extension
(c) Angular movements: flexion, extension, and hyperextension of
the vertebral column
Figure 8.5
Movements allowed by synovial joints.
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