The important parts of the cervical spine include
- bones and joints
- nerves
- connective tissues
- muscles
- spinal segments
This section highlights important structures in
each category.
Bones and Joints
The human spine
is made up of 24 spinal bones, called
vertebrae. Vertebrae are stacked on top of one
another to form the spinal column. The spinal
column is the body's main upright support.
The first seven vertebrae make up the cervical
spine. Doctors often refer to these vertebrae as
C1 to C7. The cervical spine starts where the top
vertebra (C1) connects to the bottom of the skull. The
cervical spine curves slightly inward and ends where
C7 joins the top of the thoracic spine (the
chest area).
The base of the skull sits on top of C1, also
called the atlas.
Two thickened bony arches form a large hole through
the center of the atlas. The opening is large because
the spinal cord is wider where it first exits the
brain and skull. Compared to other vertebrae, the
atlas also has much wider bony projections pointing
out to each side.
The atlas sits on top of the C2 vertebra. The C2 is
called the axis.
The axis has a large bony knob on top, called the dens.
The dens points up and fits through a hole in the
atlas. The joints of the axis give the neck most of
its ability to turn to the left and right.
Each vertebra is made of the same parts. The main
section of each cervical
vertebra, from C2 to C7, is formed by a round
block of bone, called the vertebral body. A
bony ring attaches to the back of the vertebral body.
This ring has two parts. Two pedicle bones
connect directly to the back of the vertebral body.
Two lamina bones join the pedicles to complete
the ring. The lamina bones form the outer rim of the
bony ring. When the vertebrae are stacked on top of
each other, the bony rings form a hollow tube that
surrounds the spinal cord. The laminae provide a
protective roof over the spinal cord.
A bony knob projects out at the point where the two
lamina bones join together at the back of the spine.
These projections, called spinous processes,
can be felt as you rub your fingers up and down the
back of your spine. The largest bump near the top of
your spine is the spinous process of C2. At the base
of the neck where the cervical and thoracic spines
join together, you'll feel another large spinous
process. That's C7.
Each vertebra in the spine has two bony knobs that
point out to the side, one on the left and one on the
right. These bony projections are called transverse
processes. The atlas has the widest transverse
processes of all the cervical vertebrae. Unlike the
rest of the spine, the neck vertebrae have a hole that
passes down through each transverse process. This
hole, called the transverse foramen, provides a
passageway for arteries that run up each side of the
neck to supply the back of the brain with blood.
Between each pair of vertebrae are two joints
called facet
joints. These joints connect the vertebrae
together in a chain but slide against one another to
allow the neck to move in many directions. Except for
the very top and bottom of the spinal column, each
vertebra has two facet joints on each side. The ones
on top connect to the vertebra above; the ones below
join with the vertebra below.
The surfaces of the facet joints are covered by
articular cartilage. Articular cartilage is a
smooth, rubbery material that covers the ends of most
joints. It allows the ends of bones to move against
each other smoothly, without friction.
On the left and right side of each vertebra is a
small tunnel called a neural
foramen. ("Foramina" is the plural
term.) The two nerves that leave the spine at each
vertebra go through the foramina, one on the left and
one on the right. The intervertebral disc (described
later) sits directly in front of the opening. A bulged
or herniated disc can narrow the opening and put
pressure on the nerve. A facet joint sits in back of
the foramen. Bone spurs that form on the facet joint
can project into the tunnel, narrowing the hole and
pinching the nerve.
Nerves
The hollow tube formed by the bony ring on the back
of the spinal column surrounds the spinal
cord as it passes through the spine. The
spinal cord is a similar to a long wire made up of
millions of nerve fibers. Just as the skull protects
the brain, the bones of the spinal column protect the
spinal cord.
The spinal cord travels down from the brain through
the spinal column. Two large nerves branch off the
spinal cord from each vertebra, one on the left and
one on the right. The nerves pass through the neural
foramina. These spinal nerves group together to form
the main nerves that go to the limbs and organs. The
nerves that come out of the cervical spine go to the
arms and hands.
Connective Tissues
Ligaments
are strong connective tissues that attach bones to
other bones. (Connective tissues are networks
of fiber that hold the cells of the body together.)
Several long ligaments connect on the front and back
sections of the vertebrae. The anterior
longitudinal ligament runs lengthwise down the
front of the vertebral bodies. Two other ligaments run
full length within the spinal canal. The posterior
longitudinal ligament attaches on the back of the
vertebral bodies. The ligamentum flavum is a
long elastic band that connects to the front surface
of the lamina bones.
A special type of structure in the spine called an
intervertebral disc is also made of connective
tissue. The fibers of the disc are formed by special
cells, called collagen cells. The fibers may be
lined up like strands of nylon rope or crisscrossed
like a net.
An intervertebral disc is made of two
parts. The center, called the nucleus, is
spongy. It provides most of the shock absorption in
the spine. The nucleus is held in place by the
annulus, a series of strong ligament rings
surrounding it.
Muscles
The anterior cervical area is covered with muscles
that run from the rib cage and collar bone to the
cervical vertebrae, jaw, and skull. The posterior
cervical muscles cover the bones along the back of the
spine and make up the bulk of the tissues on the back
of the neck.
Spinal Segment
A good way to understand the anatomy of the
cervical spine is by looking at a spinal
segment. Each spinal segment includes two
vertebrae separated by an intervertebral disc, the
nerves that leave the spinal cord at each vertebra,
and the small facet joints that link each level of the
spinal column.
The intervertebral disc separates the two vertebral
bodies of the spinal segment. The disc normally works
like a shock absorber. It protects the spine against
the daily pull of gravity. It also protects the spine
during heavy activities that put strong force on the
spine, such as jumping, running, and lifting.
The spinal segment is connected by a facet joint,
described earlier. When the facet joints of the
cervical spine move together, they bend and turn the
neck.