Download Anatomy Of The vertebral column

Spine Course Anatomy
Anatomy of the vertebral column
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Studying the anatomy of the spine will leave you in awe of its function and structure. We will
learn the anatomy and function of
Vertebral bone structure
Functional spinal unit
Spinal disks and ligaments
Articulating (moving) joints
The four regions of the spine
Anterior and posterior longitudinal ligaments
Major muscles of the back
Central and peripheral nervous system
Functional spinal unit
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The functional spinal unit, or FSU, simply refers to two vertebrae, the disk between them, and
the ligaments connecting them.
If you understand the FSU, it will be much easier to
understand the more advanced topics ahead.
External vertebral structure
All the vertebrae have the same general structure, with modifications in the different regions of
the spine. This animation shows a representative vertebra so we can examine the basic
structures.
The vertebral body is the roughly cylindrical portion of the vertebra. It carries
most of the weight (about 80%) of the structures above it.
Its superior and inferior
surfaces are adjacent to the intervertebral disks, but do not form a true joint with the disks.
The articulating facets form true joints (synovial joints) with the corresponding facets on the
adjacent vertebrae.
The surface of the facet is articular cartilage, forming a sliding joint and giving the spine
flexibility and stability.
The spinous process protrudes from the posterior aspect of the spine in a slightly downward
direction.
It serves as the attachment for several muscles and is tied to other spinous processes by a
strong ligament.
Touch one of yours!
The transverse processes protrude from the lateral aspects of the spine.
They serve as an attachment for muscles and are tied to other processes by ligaments.
The spinal and transverse processes act as levers, allowing muscles to more easily stabilize
and move the vertebral column.
The lamina connect the pedicles to complete a protective ring of bone surrounding the spinal
cord.
Now we see the facets from the opposite (contralateral) side of the body. The facets of each
vertebra articulate with the complimentary facets on the adjacent vertebrae like hands pressing
against each other.
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The facet's surface is articular cartilage that forms a sliding joint, giving the spine flexibility and
stability.
The lamina connect the pedicles to complete a protective ring of bone surrounding the spinal
cord.
The spinous process and inferior facets connect to the lamina.
In the inferior view we are introduced to two new key sructures, the vertebral foramen and the
pedicles.
The pedicles are important because they connect the posterior structures to the vertebral body.
They also provide the mass important to many interventional techniques.
The vertebral foramen contains the spinal cord. Its integrity is key for the normal functioning of
the nervous system.
The lamina connect the pedicles to complete a protective ring of bone surrounding the spinal
cord.
The spinous process and inferior facets connect to the lamina.
In the superior view we again see the vertebral foramen and the pedicles.
The pedicles are important because they connect the posterior structures to the vertebral body.
They also provide the mass important to many interventional techniques.
The vertebral foramen contains the spinal cord. Its integrioty is key to the normal nural
functioning of the body.
Great! You have now seen the key basic structures of the vertebra. Remember this lesson, and
you will be ahead of the game.
Internal vertebral structure
The vertebra is composed of a shell of cortical bone (compact, hard, strong) and an interior of
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cancellous bone (porous, mostly liquid). The same structure is found in many bones and
provides a balance of strength and weight. Cancellous bone has a trabecular (sponge-like)
structure. This mesh is constantly restructuring in response to stress (Wolf's Law) and the
body's need for calcium. (Bone restructuring is the subject of a different course in this series.)
Osteoporosis is a breakdown of the trabeculae.
Intervertebral disks
The disks of the spine have two basic components: the annulus fibrosis and the nucleus
pulposus. Together they form a system providing strength, shock absorption, and flexibility.
In this image, you can see the outer zone of the annulus fibrosis. Its crossing collagen fibers are
of high tensile strength and provide most of the structural strength to the disk. The crisscross
pattern increases the composite's flexibility and strength.
At the center is the nucleus pulposa, a gelatinous body which contains about 80% water.
It is incompressible and serves to distribute the forces placed upon it.
The annulus fibrosis consists of two zones. The outer zone contains the strong collagen fibers.
The outer zone blends into the softer fibrous tissues of the inner zone. The inner zone assists
with absorbing shocks and distributing loads.
The annulus fibrosis consists of two zones. The outer zone contains the strong collagen fibers.
The outer zone blends into the softer fibrous tissues of the inner zone. The inner zone assists
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with absorbing shocks and distributing loads.
Facet joints
Each vertebra (except the uppermost) has two pairs of facet (little face) joints. One pair orients
upward, toward the superior vertebra, and the other pair faces downward toward the inferior
vertebra. Each facet surface is covered with articular cartilage that acts as a bearing surface.
Side note: the facet joints are more formally called zygapophyseal, or simply, apophyseal joints.
In this image, you can see the superior articular facets. The white surface is the articular
cartilage.
As we assemble the spinal motion unit, the respective facets connect to form a facet joint.
The facet joint is enclosed by connective tissue and filled with lubricating synovial fluid, making
it a true synovial joint.
The facet joints help to stablize and strengthen the spinal column.
The vertebral body carries roughly 80% of the load on the spine, with the facets carrying the
remaining 20%.
Let's look at motions of the spine (these are exagerated for clarity). You can see the role of the
facet joints.
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Compression and decompression.
Rotating right and left.
FSU ligaments
There are several ligaments that are local to the functional spinal unit. The most significant are
the interspinous ligament and the pairs of intertransverse ligaments and the ligamenta flava.
Again these ligaments are part of the complex system that contributes to the stability and
flexibility of the vertebral column.
Motion unit muscles
There are several pairs of ligaments that are local to the spinal mition unit. The most signifiant
are the two intertransverse ligaments, interspinous ligaments, and the two ligamenta flava.
Again these ligaments are part of the complex sytem that contributes to the stability and
flexibility of the vertebral column.
Side note: the facet joints are more formally called zygapophyseal or, more simply, apophyseal
Joints.
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Regions of the vertebral column
Here we will examine the four regions of the spine in more detail.
Each or these regions has unique characteristics that distinguish it from the other regions.
Each of the four regions of a normal spine has a saggital curvature. These curves allow greater
flexibility and resistance to shock.
Each region has its own anatomy and function.
The cervical region is very flexible, allowing the head a great range of motion. Its seven
vertebrae are relatively small.
The thoracic region has relatively llittle flexibility. The ribs articulate with the thoracic vertebrae
to form a protective cage for the heart and lungs.
The lumbar region supprts the weight of the upper body. The vertebrae are relatively large, and
the disks subject to disease.
The adult sacral region is made up of two bones: the sacrum and the coccyx. The sacrum joins
the pelvis to transfer weight to the legs and forms a portion of the pelvic floor.
Male (left) and female (right) pelvis. The many differences are a significant example of human
sexual dimorphism. Why?
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Cervical region
The cervical region has seven vertebrae: C1 through C7.
C1 and C2 differ significantly from the other vertebrae. They are similar to a ball and socket
joint, giving the head its great flexibility.
C2 through C6 have bifid (split in two) spinal processes, permitting more muscle and ligament
attachment for finer control of the head.
The spinal process of C7 is larger and longer than the others. It is the first palpable spinal
process and is called the vertebra prominens.
Go ahead and check yours.
Only the cervical vertebrae have "holes" through their pedicles called transverse foramina. The
transverse foramina protect the vertebral arteries passing through them.
Thoracic region
The thoracic region has 12 vertebrae: T1 through T12. The most striking feature of the thoracic
region of the spine is that the vertebrae articulate with the ribs. This forms a protective cage
around the vital organs and structures in the chest.
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Another feature that distinguishes the thoracic region is its relative inflexibility compared to the
cervical and lumber regions. This provides additional protection to the chest cavity. The twelve
ribs are connected to the vertebrae by ligaments and joints.
T1 through T12 also have additional facets, called costal facets, to interface with the ribs.
Lumbar region
The lumbar region contains five vertebrae, L1 through L5. Since the lumbar is at the lower
(caudal) end of the spine, it endures the greatest wear and tear. The vertebgral bodies are
large, as are the transverse and spinal processes.
Interventions in the lumbar region often involve fixation of the vertebrae and disks with rigid rods
secured by metal screws passing through the vertebral pedicles.
Sacral region
The sacral region of an adult contains two bones: the large sacrum and the coccyx, or tail bone.
The two bones are connected at the sacrococcygeal joint. The curvature of the sacral region is
kyphotic (forming a "hump" on the back). The sacrum forms an articulating joint with the two iliac
bones of the pelvis: the sacroiliac joint.
*The name, sacrum, comes from ancient Latin "os sacrum" (holy bone). Some think this is
because it is home to the female reroductive system. The coccyx took a less noble route, being
named after its resemblamce to the beak of a cuckoo; refering to the sound made in its vicinity.
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The eight sacral foramina (holes) allow the lower spinal nerves to pass from interior to the spinal
column to the lower body.
Vertebral comparison
The vertebrae of the cervical, thoracic, and lumbar regions vary in size and structure. In general
vertebrae become larger and stronger, progressing cephalid to caudal, reflecting the increasing
axial load.
The cervical region is very flexible and vertebrae contain transverse foramina.
Thoracic vertebrae have overlapping spinus processes and the region is relatively inflexible.
They have costal facets that interface with the ribs.
Lumbar vertebrae are strong. Their transverse processes are so large that they are also called
costal processes because they resemble primitive ribs.
Major spinal ligaments
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The anterior and posterior longitudinal ligaments are the major stabilizers for flexion and
extension motions of the spine. The posterior longitudinal ligament (PLL) runs along the
posterior surface of the vertebral body. It extends from the skull base into the sacral canal.
The PLL lies within the vertebral foramen. This ligament bonds securly to the posterior face of
the vertebral bodies, but only loosely to the interevetebral disks.
The anterior logintudinal ligament (ALL) runs along the anterior surface of the vertebral body.
It extends from the skull base into the sacral canal. This ligament also bonds securly to the
vertebral bodies, but only loosely to the interevetebral disks.
Back muscles
This is a quick review of some of the muscles of the back. It is not meant to be a
comprehensive lesson, but just provide an overview of the complex musculature of the back.
The most superficial muscle is the trapezious. It connects medially to the spinal processes.
Caudal to the trapezius are the latissimus dorsi.
Both of these large muscles are superficial to what are called the intrinsic muscles of the back.
The "long" muscle is the longissimus. It connects to the transverse processes in the lumbar
region and the thoracic region.
The quadratus lumborum stretches from the superior edge of the pelvis (illium) and connects to
the lowest rib and the tips of the lumbar transverse processes.The multifidus muscles fill the
space between the spinal and transverse processes and work to stabilize each joint.The lateral
intertraversarious muscles help stabilize adjacent vertebrae. The semispinalis thoracis muscles
help stabilize the thoracic region. The semispinalis capitus muscles help to tilt the head from
side to side. The capitis muscles help to extend and flex the head.
Vertebral arteries
The paired vertebral arteries, like the carotid arteries, supply oxygenated blood to the brain.
They enter the spine at the transverse foramina of C6 and proceed through the transverse
foramina of C6 to C1 and then into the cranium.
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Spinal cord and nerve branches
Below the head, all the nerves of the human body are connected through the spinal cord to the
brain. Although the details can be extremely complex, a basic understanding of the system is
well within our scope.
Central & peripheral nervous systems
The nervous system can be physically divided into the central nervous system and the
peripheral nervous system.
The central nervous system is made up of the brain (the body's CPU) and the spinal cord that
resides within the vertebral foramen. The central nervous system is encapsulated in a tough
membrane called the dura mater (or just the dura). The spinal cord is a signal highway that
transmits all information to and from the brain and the body.
Pairs of nerve groups branch out of the spinal cord at each spinal joint to join the peripheral
nervous system.
Spinal cord and nerve roots
The cross section of the spinal cord shows "grey matter" surrounded by "white matter." The
spinal cord is covered by the dura mater (not shown).
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The peripheral nervous system can again be divided into motor and sensory (or more properly
somatosensory) nerves. The sensory nerves carry information to the brain about pressure,
touch, temperature, and pain. In turn the brain excites the motor neurons that control the
muscles.
All the motor nerve roots exit the sipnal cord from the anterior (or ventral) aspect.
All the sensory nerve roots enter the spinal cord through the posterior (or dorsal) surface. All
roots pass through the intervertebral foramen and join to form the spinal nerve.
Another critical component of the spinal cord is the autonomic nervous system. As you can
guess by the name, these nerves function to regulate the organs of the body without our
conscious control.
Motor and sensory nerves
The spinal nerves continue to separate and branch out until the final connections to the millions
of sensors and actuators are complete.
The sensory nerves are more delicate than the motor nerves. They manifest symptoms of
neurological problems sooner than the more robust motor neurons.
The pressure of a ruptured disk may first induce numbness in a limb. As the disease
progresses, weakness in the related muscles may develop.
Spinal nerves and function
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The C1 spinal nerve exits ABOVE the C1 vertebra. This nomenclature continues until nerve C8
exits BELOW the C7 vertebra.
From then on the spinal nerves take their names from the vertebrae above them. (Here "above"
refers to cephalid, but you knew that.)
Breathing Head & neck movement. Heart rate
Shoulder movement
Wrist and elbow movement
Hand and finger movement
Abdominal muscles, trunk stability
Temperature stability
Sexual function
Hip motion
Knee Extension
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Foot motion
Knee flexion
Sexual organs
Anal control
Spine anatomy recap
The vertebrae have a dense, strong shell of cortical bone, enclosing cancellous bone, having a
more porous structure
Disks have strong, fibrous outer bands, the annulus fibrosis, enclosing the jelly-like, but
incompressible, nucleus pulposus.
Articulating facet joints, together with the disks, allow motion of the spine.
The posterior longitudinal ligament (PLL) and the anterior longitudinal ligament (ALL) link the
vertebral bodies for more stability.
Vertebral processes are linked by the interspinous ligaments, pairs of intertransverse ligaments,
and the pairs of ligamenta flava connecting the pedicles.
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The spine has four anatomical regions: cervical, thoracic, lumbar, and sacral. Each region has a
distinct curvature. The physical structure of individual vertebrae varies for each region.
The brain and spinal cord make up the central nervous system. All other nerves make up the
peripheral nervous system. The spinal cord branches out into nerve trunks at each joint. These
trunks connect to many specific regions of the body.
QUIZ
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