spine is made up of 24 small bones (vertebrae) that are stacked on top
of each other to create the spinal column. Between each vertebra is
a soft, gel-like cushion called a disc that helps absorb pressure and
keeps the bones from rubbing against each other. Each vertebra is held
to the others by groups of ligaments. Ligaments connect bones to bones;
tendons connect muscles to bones. There are also tendons that fasten
muscles to the vertebrae. The spinal column also has real joints (just
like the knee or elbow or any other joints) called facet joints. The
facet joints link the vertebrae together and give them the flexibility
to move against each other.
vertebra has a hole in the center, so when they stack on top of each
other they form a hollow tube that holds and protects the entire spinal
cord and its nerve roots. The spinal cord itself is a large collection
of nerve tissue that carries messages from your brain to the rest of
your body. In order for your body to function, you need your nerves.
The spine branches off into thirty-one pairs of nerve roots. These roots
exit the spine on both sides through spaces (neural foramina) between
spine itself has three main segments: the cervical spine, the thoracic
spine, and the lumber spine. The cervical is the upper part of the spine,
made up of seven vertebrae (bones). The thoracic is the center portion
of the spine, consisting of 12 vertebrae. The lower portion of the spine
is called the lumbar spine. It is usually made up of five vertebrae,
however, some people may have six lumbar vertebrae. Having six vertebrae
does not seem to cause a problem. Below the lumbar spine is the sacrum.
The sacrum is actually a group of specialized vertebrae that connects
the spine to the pelvis. During development (those nine months before
birth), these vertebrae grow together or fuse creating one large "specialized"
vertebral bone that forms the base of your spine and center of your
pelvis. The nerves that leave the spine in the sacral region control
the bowel and bladder functions and give sensation (feeling) to the
The normal spine
has an "S"-like curve when looking at it from the side. This
allows for an even distribution of weight. The "S" curve helps
a healthy spine withstand all kinds of stress. The cervical spine curves
slightly inward, the thoracic curves outward, and the lumbar curves
inward. Even though the lower portion of your spine holds most of the
body's weight, each segment relies upon the strength of the others to
of the Spine:
The individual bones of the spine are the vertebrae. These are the building
blocks of the spinal column. The vertebrae protect and support the spinal
cord. They also bear the majority of the weight put upon your spine.
The body of each vertebra is the large, round portion of bone. The body
of each vertebra is attached to a bony ring. When the vertebrae are
stacked one on top of the other, this ring creates a hollow tube where
the spinal cord passes through.
The bony ring attached to the vertebral body consists of several parts.
First, the laminae extend from the body to cover the spinal canal, which
is the hole in the center of the vertebrae. Second, the spinous process
is the bony portion opposite the body of the vertebra. You feel this
part if you run your hand down a person's back. Then there are two transverse
processes (little bony bumps), where the back muscles attach to the
vertebrae. Finally, the pedicle is a bony projection that connects to
both sides of the lamina.
The vertebra, like all bones, has an outer shell called cortical bone
that is hard and strong. The inside is made of a soft, spongy type of
bone that is called cancellous bone.
The intervertebral discs are flat, round "cushions" that act
as shock absorbers between each vertebra in your spine. There is one
disc between each vertebra. Each disc has a strong outer ring of fibers
called the annulus, and a soft, jelly-like center called the nucleus
The annulus is the disc's outer layer and the strongest area of the
disc. It also helps keep the disc's center intact. The annulus is actually
a strong ligament that connects each vertebra together.
The mushy nucleus of the disc serves as the main shock absorber. The
nucleus is made up of tissue that is very moist because it has high
water content. The water content helps the disc act like a shock absorber
- somewhat like a waterbed mattress.
The facets are the "bony knobs" that meet between each vertebra
to form the facet joints that join your vertebrae together. There are
two facet joints between each pair of vertebra, one on each side. They
extend and overlap each other to form a joint between the neighboring
vertebra facet joints. Without the facet joints, you would not have
flexibility in your spine, and you could only move in very straight
and stiff motions.
The facet joints are what are known as synovial joints. A synovial joint,
such as the knee or elbow, is a structure that allows movement between
two bones. In a synovial joint, the ends of the bones are covered with
a material called articular cartilage. This material is a slick spongy
material that allows the bones to glide against one another without
Surrounding the facet joint is a watertight sack made of soft tissue
and ligaments. This sack creates what is called the "joint capsule".
The ligaments are soft tissue structures that hold the two sides of
the facet joint together. The ligaments around the facet joint combine
with the synovium to form the joint capsule that is filled with fluid
(synovial fluid). This fluid lubricates the joint to decrease the friction,
just like oil lubricates the moving parts of a machine.
The neural foramen is the opening between every two vertebrae where
the nerve roots exit the spine. The nerve roots travel through the foramen
to reach the rest of your body. There are two neural foramina between
each pair of vertebrae - one on each side. Without the foramen, nerve
signals could not travel to and from the brain to the rest of your body.
Without nerve signals, your body would not be able to function.
and Nerve Roots
The spinal cord is a column of millions of nerve fibers that run through
your spinal canal. It extends from the brain to the area between the
end of your first lumbar vertebra and top of your second lumbar vertebra.
At the second lumbar vertebra, the spinal cord divides into several
different groups of fibers that form the nerves that will go to the
lower half of the body. For a small distance, the nerves actually travel
through the spinal canal before exiting out the neural foramen. This
collection of nerves is called the cauda equina while it is still inside
the spinal canal.
A protective membrane
called the dura mater covers the spinal cord. The dura mater forms a
watertight sack around the spinal cord and the spinal nerves. Inside
this sack, the spinal cord is surrounded by spinal fluid.
The nerve fibers
in your spinal cord branch off to form pairs of nerve roots that travel
through the small openings (foramina) between your vertebrae. The nerves
in each area of the spinal cord connect to specific parts of your body.
This is why damage to the spinal cord can cause paralysis in certain
areas and not others -- it depends on which spinal nerves are affected.
The nerves of the cervical spine go to the upper chest and arms. The
nerves in your thoracic spine go to your chest and abdomen. The nerves
of the lumbar spine then reach to your legs, bowel, and bladder. These
nerves coordinate and control all the body's organs and parts, and let
you control your muscles.
The nerves also
carry electrical signals back to the brain that allow you to feel sensations.
If your body is being hurt in some way, your nerves signal the brain
that you have been hurt. Damage to the nerves themselves can cause pain,
tingling, or numbness in the area where the nerve travels.
The paraspinal muscles refer to the muscles next to the spine. They
support the spine and are the motor for movement of the spine. Your
joints allow flexibility and your muscles allow mobility. There are
many small muscles in the back - each controlling some part of the total
movement between all the vertebrae and the rest of the skeleton. These
muscles can be injured directly, such as when you have a pulled muscle
or muscle strain of the back muscles. The muscles can also cause problems
indirectly, such as when the muscles are in spasm after injury to other
parts of the spine.
The lowest part of the spine is called the lumber spine. This area has
five vertebrae. However, sometimes people are born with a sixth vertebra
in the lumbar region. The base of your spine (sacrum) is a fusion of
many bones, and when one of them forms as a vertebra rather than part
of the sacrum, it is called a transitional (or sixth) vertebra. This
occurrence is not dangerous and does not appear to have any serious
The lumbar spine's shape has what is called a lordotic curve. The lordotic
shape is like a backwards "C". If you think of the spine as
having an "S"-like shape, the lumbar region would be the bottom
of the "S". The vertebrae in the lumbar spine area are the
largest of the entire spine, so the lumbar spinal canal is larger than
in the cervical or thoracic parts of the spine. Because of its size,
the lumbar spine has more space for the nerves to move about.
Low back pain is
a very common complaint for a simple reason. Since the lumbar spine
is connected to your pelvis, this is where most of your weight bearing
and body movement takes place. Typically, this is where people tend
to place too much pressure, such as: lifting up a heavy box, twisting
to move a heavy load, or carrying a heavy object. Such repetitive injuries
can lead to damage to the parts of the lumbar spine.
The thoracic spine is made up of the middle 12 vertebra of the spine.
These vertebrae connect to your ribs and form part of the back wall
of the thorax (the ribcage area between the neck and the diaphragm).
This part of the spine has very narrow, thin intervertebral discs, so
there is much less movement allowed between vertebrae than in the lumbar
or cervical parts of the spine. It also has less space in the spinal
canal for the nerves. The thoracic spine's curve is called kyphotic
because of its shape, which is a regular "C"-shaped curve
with the opening of the "C" in the front.
The cervical spine is made up of the first seven vertebrae in the spine.
It starts just below the skull and ends just above the thoracic spine.
The cervical spine has a lordotic curve (a backward "C"-shape)
- just like the lumbar spine. The cervical spine is much more mobile
than both of the other spinal regions - think about all the directions
and angles you can turn your neck.
Unlike the rest
of the spine, there are special openings in each vertebra in the cervical
spine for the arteries (blood vessels that carry blood away from the
heart), as well as the spinal canal that carries the spinal cord. The
arteries that run through these openings bring blood to the brain.
Two vertebrae in
the cervical spine, the atlas and the axis, differ from the other vertebrae
because they are designed specifically for rotation. These two vertebrae
are what allow your neck to rotate in so many directions, including
looking to the side.
The atlas is the first cervical vertebra - the one that sits between
the skull and the rest of spine. The atlas does not have a vertebral
body, but does have a thick forward (anterior) arch and a thin back
(posterior) arch, with two prominent sideways masses.
The atlas sits
on top of the second cervical vertebra - the axis. The axis has a bony
knob called the odontoid process that sticks up through the hole in
the atlas. It is this special arrangement that allows the head to turn
from side to side as far as it can. Special ligaments between these
two vertebrae allow a great deal of rotation to occur between the two