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Gross Anatomy
The spinal cord extends from the foramen
magnum to the inferior border of the first lumbar vertebra. Visible features of
the spinal cord include:
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Posterior median sulcus shallow
longitudinal groove on the dorsal surface. |
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Anterior median fissure deep crease on
the ventral surface. |
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Enlargements
along the length of the spinal cord the regions devoted to processing
information associated with the limbs are enlarged. These include:
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Cervical enlargement (C5 T1) supplies nerves to the upper limb and
pectoral girdle. |
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Lumbosacral (lumbar) enlargement (L2 S3) supplies nerves to the lower limbs and pelvic
girdle. |
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Conus medullaris
The conical end of the spinal cord. |
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Filum terminale
slender thread of fibrous pia mater that extends from the tip of the
spinal cord and anchors it longitudinally. |
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Cauda equina
The spinal cord stops growing before the vertebral column. As a result the
dorsal and ventral roots continue to grow as their exit points move further
away. This collection of roots within the vertebral column at this point form
the cauda equina. |
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Spinal Cord
Segments
There are 31
spinal cord segments, 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1
coccygeal segments. Each segment is associated with the pair of spinal nerves
that arise from it. |
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Spinal Nerves
The spinal
nerves result from the fusion of dorsal and ventral roots. The
roots themselves result from the fusion of rootlets that extend from either side
of each spinal segment. The dorsal and ventral roots exit the vertebral column
through the intervertebral foramina. At the exit point there is a dorsal
root ganglion that contains the cell bodies of the sensory neurons
found in the dorsal root. The ventral root which contains motor neurons, fuses
with the dorsal root distal to the ganglion to form the spinal nerve. |
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Spinal Meninges
The spinal
meninges are specialized membranes that provide protection, physical stability
and shock absorption within the bony vertebral canal. There are three meningeal
layers:
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Dura mater
The outer
layer consists of dense irregular connective tissue. Between the dura mater and
the inner wall of the vertebral canal there is an epidural space
containing areolar connective tissue, adipose tissue and blood vessels. |
The dura mater is attached
cranially to the periosteum at the
margin of the foramen magnum and tapers
distally to form the coccygeal ligament that attaches to the
periosteum of the sacrum and coccyx. |
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Arachnoid mater
The
arachnoid is the middle meningeal layer and consists of a simple squamous
epithelium that attaches directly to the inside of the dura mater. It is
separated by the subarachnoid space that contains cerebrospinal fluid
(CSF) from the pia mater. The space between the arachnoid and pia mater is
also spanned by collagen and elastic fibers that form bundles of fibers called
arachnoid trabeculae. |
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Pia mater
The
innermost meningeal layer consists of collagen and elastic fibers that adhere
closely to the contours of the nervous tissue. Lateral extensions of the pia
mater and arachnoid mater between the dorsal and ventral roots attach to the
dura mater and are called denticulate ligaments. The denticulate
ligaments prevent side to side and inferior movement of the spinal cord. |
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