218
UNIT 2
Covering, Support, and Movement of the Body
7
are nonfunctional, those of the opposite side exert an unop-
posed pull on the spine and force it out of alignment. Scoliosis
is treated (with body braces or surgically) before growth ends to
prevent permanent deformity and breathing difficulties due to
a compressed lung.
Kyphosis
(ki-fo
9
sis), or hunchback, is a
dorsally
exaggerated
thoracic
curvature. It is particularly common in elderly people
because of osteoporosis, but may also reflect tuberculosis of the
spine, rickets, or osteomalacia.
The Vertebral Column
General Characteristics
Describe the structure of the vertebral column, list its
components, and describe its curvatures.
Indicate a common function of the spinal curvatures and
the intervertebral discs.
Some people think of the
vertebral column
as a rigid supporting
rod, but this is inaccurate. Also called the
spine
or
spinal column
,
the vertebral column consists of 26 irregular bones connected in
such a way that a flexible, curved structure results
(Figure 7.16)
.
Serving as the axial support of the trunk, the spine extends
from the skull to the pelvis, where it transmits the weight of
the trunk to the lower limbs. It also surrounds and protects the
delicate spinal cord and provides attachment points for the ribs
and for the muscles of the back and neck.
In the fetus and infant, the vertebral column consists of 33
separate bones, or
vertebrae
(ver
9
tĕ-bre). Inferiorly, nine of
these eventually fuse to form two composite bones, the sacrum
and the tiny coccyx. Te remaining 24 bones persist as indi-
vidual vertebrae separated by intervertebral discs.
Regions and Curvatures
Te vertebral column is about 70 cm (28 inches) long in an aver-
age adult and has five major regions (Figure 7.16). Te seven ver-
tebrae of the neck are the
cervical vertebrae
(ser
9
vĭ-kal), the next
12 are the
thoracic vertebrae
(tho-ras
9
ik), and the five supporting
the lower back are the
lumbar vertebrae
(lum
9
bar). Remember-
ing common meal times—7 ±M, 12 noon, and 5 PM—will help
you recall the number of bones in these three regions of the spine.
Te vertebrae become progressively larger from the cervical to the
lumbar region, as they must support greater and greater weight.
Inferior to the lumbar vertebrae is the
sacrum
(sa
9
krum),
which articulates with the hip bones of the pelvis. Te terminus
of the vertebral column is the tiny
coccyx
(kok
9
siks).
All of us have the same number of cervical vertebrae. Vari-
ations in numbers of vertebrae in other regions occur in about
5% of people.
When you view the vertebral column from the side, you can
see the four curvatures that give it its S, or sinusoid, shape. Te
cervical
and
lumbar curvatures
are concave posteriorly; the
thoracic
and
sacral curvatures
are convex posteriorly. Tese
curvatures increase the resilience and flexibility of the spine, al-
lowing it to function like a spring rather than a rigid rod.
Homeostatic Imbalance
7.2
Tere are several types of abnormal spinal curvatures
(Figure 7.17)
. Some are congenital (present at birth); others
result from disease, poor posture, or unequal muscle pull on the
spine.
Scoliosis
(sko
0
le-o
9
sis), literally, “twisted disease,” is an ab-
normal
lateral
curvature that occurs most o²en in the thoracic
region. It is quite common during late childhood, particularly
in girls, for some unknown reason. Other, more severe cases re-
sult from abnormal vertebral structure, lower limbs of unequal
length, or muscle paralysis. If muscles on one side of the body
Cervical curvature
(concave)
7 vertebrae, C
1
– C
7
Thoracic curvature
(convex)
12 vertebrae,
T
1
– T
12
Lumbar curvature
(concave)
5 vertebrae, L
1
– L
5
Sacral curvature
(convex)
5 fused vertebrae
sacrum
Coccyx
4 fused vertebrae
Anterior view
Right lateral view
C
1
T
1
2
3
4
5
6
7
8
9
10
11
12
L
1
2
3
4
5
2
3
4
5
6
7
Spinous
process
Transverse
processes
Intervertebral
discs
Intervertebral
foramen
Figure 7.16
The vertebral column.
Notice the curvatures in the
lateral view. (The terms convex and concave refer to the curvature of
the posterior aspect of the vertebral column.) (For a related image,
see
A Brief Atlas of the Human Body,
Figure 17.)
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