the spine (bending too far backward). Te posterior ligament,
which resists hyperﬂexion of the spine (bending too sharply
forward), is narrow and relatively weak. It attaches only to the
discs. However, the
, which connects ad-
jacent vertebrae, contains elastic connective tissue and is espe-
cially strong. It stretches as we bend forward and then recoils
when we resume an erect posture. Short ligaments connect each
vertebra to those immediately above and below.
is a cushionlike pad composed of
two parts. Te inner gelatinous
“pulp”) acts like a rubber ball, giving the disc its elasticity and
compressibility. Surrounding the nucleus pulposus is a strong
collar composed of collagen ﬁbers superﬁcially and ﬁbrocarti-
lage internally, the
sus; “ring of
ﬁbers”) (Figure 7.18a, c). Te anulus ﬁbrosus limits the expan-
sion of the nucleus pulposus when the spine is compressed. It
also acts like a woven strap to bind successive vertebrae together,
withstands twisting forces, and resists tension in the spine.
Sandwiched between the bodies of neighboring vertebrae,
the intervertebral discs act as shock absorbers during walking,
jumping, and running. Tey allow the spine to ﬂex and extend,
and to a lesser extent to bend laterally. At points of compression,
the discs ﬂatten and bulge out a bit between the vertebrae. Te
discs are thickest in the lumbar and cervical regions, which en-
hances the ﬂexibility of these regions.
Collectively the discs account for about 25% of the height of
the vertebral column. Tey ﬂatten somewhat during the course
of the day, so we are always a few millimeters shorter at night
than when we awake in the morning.
Severe or sudden physical trauma to the spine—for example,
from bending forward while li±ing a heavy object—may result
in herniation of one or more discs. A
, or swayback, is an accentuated
too, can result from spinal tuberculosis or osteomalacia. ²empo-
rary lordosis is common in those carrying a large load up front,
such as men with “potbellies” and pregnant women. In an attempt
to preserve their center of gravity, these individuals automatically
throw back their shoulders, accentuating their lumbar curvature.
Like a tall, tremulous ²V transmitting tower, the vertebral col-
umn cannot possibly stand upright by itself. It must be held in
place by an elaborate system of cable-like supports. In the case
of the vertebral column, straplike ligaments and the trunk mus-
cles assume this role.
Te major supporting ligaments are the
terior longitudinal ligaments
. Tese run as
continuous bands down the front and back surfaces of the verte-
brae from the neck to the sacrum. Te broad anterior ligament
is strongly attached to both the bony vertebrae and the discs.
Along with its supporting role, it prevents hyperextension of
Abnormal spinal curvatures.
Inferior articular process
(a) Median section of three vertebrae, illustrating the composition
of the discs and the ligaments
Body of a vertebra
(b) Anterior view of part of the spinal column,
showing the anterior longitudinal ligament
Ligaments and ﬁbrocartilage discs uniting the vertebrae.