258
UNIT 2
Covering, Support, and Movement of the Body
8
Flexion
Flexion
(flek
9
shun) is a bending movement, usually
along the sagittal plane, that
decreases the angle
of the joint and
brings the articulating bones closer together. Examples include
bending the head forward on the chest (Figure 8.5b) and bend-
ing the body trunk or the knee from a straight to an angled
position (Figure 8.5c and d). As a less obvious example, the arm
is flexed at the shoulder when the arm is li±ed in an anterior
direction (Figure 8.5d).
Extension
Extension
is the reverse of flexion and occurs
at the same joints. It involves movement along the sagittal
plane that
increases the angle
between the articulating bones
and typically straightens a flexed limb or body part. Examples
include straightening a flexed neck, body trunk, elbow, or
knee (Figure 8.5b–d). Continuing such movements beyond
the anatomical position is called
hyperextension
(literally,
“superextension”) (Figure 8.5b–d).
Abduction
Abduction
(“moving away”) is movement of a
limb
away
from the midline or median plane of the body, along
the frontal plane. Raising the arm or thigh laterally is an exam-
ple of abduction (Figure 8.5e). For the fingers or toes, abduction
means spreading them apart. In this case “midline” is the long-
est digit: the third finger or second toe. Notice, however, that
lateral bending of the trunk away from the body midline in the
frontal plane is called lateral flexion, not abduction.
Adduction
Adduction
(“moving toward”) is the opposite of
abduction, so it is the movement of a limb
toward
the body
midline or, in the case of the digits, toward the midline of the
hand or foot (Figure 8.5e).
Circumduction
Circumduction
(Figure 8.5e) is moving a limb
so that it describes a cone in space (
circum
5
around;
duco
5
to
draw). Te distal end of the limb moves in a circle, while the
point of the cone (the shoulder or hip joint) is more or less sta-
tionary. A pitcher winding up to throw a ball is actually cir-
cumducting his or her pitching arm. Because circumduction
consists of flexion, abduction, extension, and adduction per-
formed in succession, it is the quickest way to exercise the many
muscles that move the hip and shoulder ball-and-socket joints.
Rotation
Rotation
is the turning of a bone around its own long axis. It
is the only movement allowed between the first two cervical
vertebrae and is common at the hip (Figure 8.5f) and shoulder
joints. Rotation may be directed toward the midline or away
from it. For example, in
medial rotation
of the thigh, the femur’s
anterior surface moves toward the median plane of the body;
lateral rotation
is the opposite movement.
Special Movements
Certain movements do not fit into any of the above categories
and occur at only a few joints. Some of these special movements
are illustrated in
Figure 8.6
.
Supination and Pronation
Te terms
supination
(soo
0
pĭ-
na
9
shun; “turning backward”) and
pronation
(pro-na
9
shun;
“turning forward”) refer to the movements of the radius around
the ulna (Figure 8.6a). Rotating the forearm laterally so that the
palm faces anteriorly or superiorly is supination. In the anatomical
position, the hand is supinated and the radius and ulna are parallel.
In pronation, the forearm rotates medially and the palm
faces posteriorly or inferiorly. Pronation moves the distal end of
the radius across the ulna so that the two bones form an X. Tis
is the forearm’s position when we are standing in a relaxed man-
ner. Pronation is a much weaker movement than supination.
A trick to help you keep these terms straight: A
pro
basketball
player pronates his or her forearm to dribble the ball.
Dorsiflexion and Plantar Flexion of the Foot
Te up-and-
down movements of the foot at the ankle are given more specific
names (Figure 8.6b). Li±ing the foot so that its superior surface
approaches the shin is
dorsiflexion
(corresponds to wrist exten-
sion), whereas depressing the foot (pointing the toes) is
plantar
flexion
(corresponds to wrist flexion).
Inversion and Eversion
Inversion
and
eversion
are special
movements of the foot (Figure 8.6c). In inversion, the sole of the
foot turns medially. In eversion, the sole faces laterally.
Protraction and Retraction
Nonangular anterior and posterior
movements in a transverse plane are called
protraction
and
re-
traction
, respectively (Figure 8.6d). Te mandible is protracted
when you jut out your jaw and retracted when you bring it back.
Elevation and Depression
Elevation
means li±ing a body
part superiorly (Figure 8.6e). For example, the scapulae are el-
evated when you shrug your shoulders. Moving the elevated
part inferiorly is
depression
. During chewing, the mandible is
alternately elevated and depressed.
Opposition
Te saddle joint between metacarpal I and the
trapezium allows a movement called
opposition
of the thumb
(Figure 8.6f). Tis movement is the action taken when you
touch your thumb to the tips of the other fingers on the same
hand. It is opposition that makes the human hand such a fine
tool for grasping and manipulating objects.
Types of Synovial Joints
Although all synovial joints have structural features in com-
mon, they do not have a common structural plan. Based on
the shape of their articular surfaces, which in turn determine
the movements allowed, synovial joints can be classified further
into six major categories—plane, hinge, pivot, condylar (or el-
lipsoid), saddle, and ball-and-socket joints. Te properties of
these joints are summarized in
Focus on Types of Synovial Joints
(Figure 8.7)
on pp. 260–261.
Check Your Understanding
9.
John bent over to pick up a dime. What movement was
occurring at his hip joint, at his knees, and between his index
finger and thumb?
10.
On the basis of movement allowed, which of the following
joints are uniaxial? Hinge, condylar, saddle, pivot.
For answers, see Appendix H.
(Text continues on p. 262.)
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