Human Anatomy Vol 1

THOBAX

bodies, and two joints-right and left-between the
articular processes.
The joints between the articular processes are plane
synovial joints.
The joint between the vertebral bodies is a symphysis
(secondary cartilaginous joint). The surfaces of the
vertebral bodies are lined by thin layers of hyaline
cartilage. Between these layers of hyaline cartilage,
there is a thick plate of fibrocartilage which is called
the intervertebral disc.

Interveilebrol Dlscs

These are fibrocartilaginous discs which intervene
between the bodies of adjacent vertebrae, and bind them
together. Their shape corresponds to that of the
vertebral bodies between which they are placed. The
thickness of the disc varies in different regions of the
vertebral column, and in different parts of the same
disc. In the cervical and lumbar regions, the discs are
thicker in front thanbehind, while in the thoracic region
they are of uniform thickness. The discs are thinnest in
the upper thoracic region, and thickest in the lumbar
region.
The discs contribute about one-fifth of the length of
the vertebral column. The contribution is greater in the
cervical and lumbar regions than in the thoracic region.
Each disc is made up of the following two parts.
1 The nucleus pulposus is the central part of the disc. It
is soft and gelatinous atbirth. It is kept under tension
and acts as a hydraulic shock absorber. With
advancing age the elasticity of the disc is much
reduced (Frgs73.27a and c).
2 The annulus fibrosus forms the peripheral part of the
disc. It is made up of a narrower outer zone of colla-
genous fibres and a wider inner zone of fibrocartilage.
The fibres form laminae that are arranged in the form
of incomplete rings. The rings are connected by strong
fibrous bands. The outer collagenous fibres blend
with the anterior and posterior longitudinal liga-
ments (Figs 13.27a to c).

Funclions

1 The intervertebral discs give shape to the vertebral
column.
2 They act as a remarkable series of shock absorbers
or buffers.
3 Because of their elasticity they allow slight
movement of vertebral bodies on each other, more
so inthe cervical and lumbar regions. When the slight
movements at individual discs are addeid together,
they become considerable.

ligomenls Connecling Adjocent ]lebroe

Apart from the intervertebral discs and the capsules
around the joints between the articular processes,

Annulus fibrosus

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Laminae of annulus fibrosus

(b)

Upper cartilaginous plate

Upper vertebra

Nucleus pulposus

Lower vertebra

(c)

Flga 13.27 a lo c: Structu re of an intervertebral disc. (a) Superior

view, (b) arrangement of laminae, and (c) vertical section

adjacent vertebrae are connected by several ligaments

which are as follows.

1 The anterior longitudinal ligament passes from the

anterior surface of the body of one vertebra to

another. Its upper end reaches the basilar part of the

occipital bone (Fig. 1.3.27a).

2 The posterior longitudinal ligament is present on the

posterior surface of the vertebral bodies within the

vertebral canal. Its upper end reaches the body of

the axis vertebra beyond which it is continuous with

tl:;e membrana tectoria.

3 The intertransaerse ligamenfs connect adjacent

transverse processes.

4 The interspinous ligaments connect adjacent spines.

5 The supraspinous ligaments connect the tips of the

spines of vertebrae from the seventh cervical to the

sacrum. In the cervical region, they are replaced by

the ligamentum nuchae.

Short arm of lever

Lower cartilaginous plate

FIg. 13.28: Diagram comparing a rib to a lever