A New Beginning
A study of the spinal column and the backbones that facilitate it, I believe, will afford me a better understanding of the relationships between circulation and structure. Connections of bone, nerves and muscles will be studied as well, lending to my emerging understanding of connectivity and a greater overall vision of the project.
A discourse on the spinal column and the supporting bones
VERTEBRAL COLUMN
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Purpose of the Vertebrae
Protection |
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Base for Attachment |
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Structural Support |
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Flexibility and Mobility |
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Atlas
The Atlas is the first cervical vertebra and therefore abbreviated C1. This
vertebra supports the skull. Its appearance is different from the other spinal
vertebrae. The atlas is a ring of bone made up of two lateral masses joined at
the front and back by the anterior arch and the posterior arch.
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FACET JOINTS
A joint is where two or more bones are joined. Joints allow motion (articulation). The joints in the spine are commonly called Facet Joints. Other names for these joints are Zygapophyseal or Apophyseal Joints. Each vertebra has two sets of facet joints. One pair faces upward (superior articular facet) and one downward (inferior articular facet). There is one joint on each side (right and left). Facet joints are hinge–like and link vertebrae together. They are located at the back of the spine (posterior).
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Facet joints are synovial joints. This means each joint is surrounded by a capsule of connective tissue and produces a fluid to nourish and lubricate the joint. The joint surfaces are coated with cartilage allowing joints to move or glide smoothly (articulate) against each other.
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These joints allow flexion (bend forward), extension (bend backward), and twisting motion. Certain types of movement are restricted. The spine is made more stable due to the interlocking nature to adjacent vertebrae.
INTERVERTEBRAL DISCS
The intervertebral discs make up one fourth of the spinal column's length. There are no discs between the Atlas (C1), Axis (C2), and Coccyx. Discs are not vascular and therefore depend on the end plates to diffuse needed nutrients. The cartilaginous layers of the end plates anchor the discs in place.
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The intervertebral discs are fibrocartilaginous cushions serving as the
spine's shock absorbing system, which protect the vertebrae, brain, and other
structures (i.e. nerves). The discs allow some vertebral motion: extension and
flexion. Individual disc movement is very limited – however considerable
motion is possible when several discs combine forces.
Annulus Fibrosus and Nucleus Pulposus
Intervertebral discs are composed of an annulus fibrosus and a nucleus pulposus.
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The annulus fibrosus is a strong radial tire–like structure made up of
lamellae; concentric sheets of collagen fibers connected to the vertebral end
plates. The sheets are orientated at various angles. The annulus fibrosus
encloses the nucleus pulposus.
Although both the annulus fibrosus and nucleus pulposus are composed of water,
collagen, and proteoglycans (PGs), the amount of fluid (water and PGs) is
greatest in the nucleus pulposus. PG molecules are important because they
attract and retain water. The nucleus pulposus contains a hydrated gel–like
matter that resists compression. The amount of water in the nucleus varies
throughout the day depending on activity.
LIGAMENTS
Ligaments are fibrous bands or sheets of connective tissue linking two or more bones, cartilages, or structures together. One or more ligaments provide stability to a joint during rest and movement. Excessive movements such as hyper–extension or hyper–flexion, may be restricted by ligaments. Further, some ligaments prevent movement in certain directions.
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Three of the more important ligaments in the spine are the Ligamentum Flavum, Anterior Longitudinal Ligament and the Posterior Longitudinal Ligament.
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The Ligamentum Flavum forms a cover over the dura mater: a layer of tissue that protects the spinal cord. This ligament connects under the facet joints to create a small curtain over the posterior openings between the vertebrae.·
The Anterior Longitudinal Ligament attaches to the front (anterior) of each vertebra. This ligament runs up and down the spine (vertical or longitudinal).·
The Posterior Longitudinal Ligament runs up and down behind (posterior) the spine and inside the spinal canal.
NERVE STRUCTURES OF THE SPINE
Nerves control the body’s functions including the vital organs, sensation,
and movement. The nervous system receives information and initiates an
appropriate response. It is affected by internal and external factors (i.e.
stimulus).
Nerves follow tracts and cross over junctions called Synapses. Simplified, it is
a complex communicative process between nerves conducted by chemical and/or
electrical changes.
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Central Nervous System (CNS)
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The
Backbone
The spine, or backbone, is a column of
separate bones called vertebrae. The main roles of the spine are to support the
body and to provide protection for the spinal cord, which is the large bundle of
nerves that connects the brain to the rest of the body. The vertebrae are linked
by ligaments and pads of a flexible material called fibrocartillage.
Thoracic
vertebrae
Twelve thoracic vertebrae are stacked in the chest, each with a shallow socket on either side where the ribs join the spine. Vertebrae are larger and sturdier in the lower back than in the upper back in order to support more weight. The ten uppermost vertebrae, those that support the neck and head, emphasize stability. Their structure includes additional bumps and hollows that lock neighboring links in the spinal column together.
Spinal
column
Although
individual vertebrae move little from one to the next, the human spinal column
as a whole is a chain flexible enough to allow us to touch our toes. Its unique
S-shape centers the weight of our long bodies over our feet, keeping us from
toppling. Animals that walk on all four legs have straighter spines that provide
even support for their horizontal bodies.
Atlas
& Axis
The
top two vertebrae in the spinal column are specialized to allow the head a
greater range of movement than would be possible with normal vertebrae. A stable
ball-and-socket joint accommodates both side-to-side and up-and-down motion.
Ribs
Rib,
in anatomy, a long, slender bone attached to the backbone that curves around the
chest cavity, or thorax. The front of each rib ends in a short, flexible section
of cartilage. Ribs occur in pairs and are found in almost all vertebrates, or
animals with backbones.
In fish and other lower vertebrates, ribs extend along the entire length of the backbone. In higher vertebrates, including birds and mammals, ribs are present only in the chest cavity. Many of the ribs in these animals connect with the sternum, or breastbone, at the front of the chest to form the thoracic cage, which protects the lungs and heart. In addition to providing protection and support, the ribs contribute to the mechanics of breathing in higher vertebrates. The flexibility of the thoracic cage, which is made possible by rib cartilage, permits inhaling and exhaling.
Humans
normally have 12 pairs of ribs, with one pair extending from each of the
thoracic vertebra. The vertebrae are the 33 individual bones that comprise the
backbone, or spinal column. The upper seven pairs of ribs, called true ribs, are
connected to the breastbone by the cartilage at the front of each rib. The
remaining five pairs are called false ribs. The upper three pairs of false ribs
are attached to the backbone, with each rib connected to the cartilage of the
rib above it. The last two pairs of false ribs are called floating ribs because
they are attached only to the backbone, and not to the breastbone or any other
rib. Occasionally an extra pair of very short ribs extends from the lowest
vertebra in the neck.