Spinal Anatomy: Regions and Vertebrae

The spine, commonly referred to
as the spinal column or backbone, consists of 33 specialized bones known as
vertebrae. Although there are technically 24 movable vertebrae, the sacrum
and coccyx comprise additional fused sections. The spine is characterized by
four “normal curves,” which are crucial for its functionality and
can be shaped by genetics and posture. The four curves include the cervical
lordotic curve, thoracic kyphotic curve, lumbar lordotic curve, and kyphotic
curve of the sacrum and coccyx.

The spine is categorized into five distinct regions: cervical, thoracic,
lumbar, sacrum, and coccyx. When viewed from the side, healthy spinal curves
are evident. The cervical spine, labeled C1–C7, demonstrates flexibility and
curves inward. Conversely, the thoracic spine (T1–T12) curves outward and,
if excessively bent (over 50 degrees), is termed kyphosis. The lumbar spine
(L1‚ÄìL5) mirrors the cervical spine’s curvature but is primarily adapted for
forward and backward bending. The sacrum comprises five fused vertebrae,
forming the spine’s base, while the coccyx consists of three to five fused
vertebrae, whose specific shape can vary significantly among
individuals.

The development of these spinal curves is a blend of genetic and
environmental influences. The primary curves, found in the thoracic and
sacral regions, develop in utero, while secondary curves, seen in the
cervical and lumbar regions, arise postnatally. The cervical curve begins to
form as infants learn to lift their heads, completing its development around
nine months. The lumbar curve solidifies by the age of ten. Secondary curves
are less stable due to their dependence on muscular balance, leading to more
common issues in these regions compared to the thoracic and sacral
areas.

Each vertebra features a robust structure, with a central body, a vertebral
arch, and a vertebral foramen, where the spinal cord passes. Interconnected
by two thick ligaments and separated by intervertebral discs, each segment
supports motion while protecting spinal nerves. Discs, which act as shock
absorbers, allow limited movement, while facet joints regulate the overall
movement of the spinal column. Each vertebral region exhibits different structural
variations affecting mobility and stability.

Interestingly, astronauts experience a temporary increase in height in
space due to the expansion of intervertebral discs in the absence of
Earth’s gravity. This phenomenon underscores the dynamic interplay between
gravity and spinal structure, which can fluctuate throughout the day based on
mechanical stressors.

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