So let's talk about some introductory and orientation to the spinal cord. When we think
about the spinal cord, we divide it into 4 segments. There is the cervical, thoracic, lumbar,
and sacral segments and you can see those here. Each of these segments contains
both gray matter and white matter tracts. The gray matter contains the cell bodies
of the motor and then the key input tracts for the sensory fibers at each level of the
spinal cord, and that here is depicted in pink. The yellow are the white matter tracts
that surround the gray matter in the spinal cord. And there are a few things to take
away from this schematic. First of all, there's a different amount of gray matter in
each area and segment of the spinal cord. We have a lot of cell bodies in the cervical
region and so more gray matter and more cell bodies arising out of that area to give
our arms all of the innervation that they need. There is less gray matter in the thoracic
spine where there are only a small number of nerve roots going to the thoracic body
in that area. Down in the lumbar spine which gives rise to all the nerves leaving the
lumbar spine to the legs and arriving in from the legs, we again see more gray matter.
And so you can see the variation in the amount of gray to white matter in each area
of the spinal cord. Here, we're looking at the spinal cord laterally and there are a few
things to take away from this. The vertebral bodies of the spine extend all the way
from the top of the head or the base of the head and the skull all the way down to the
end of the buttocks, but the spinal cord typically ends higher than that. We see the
cervical, thoracic, lumbar, and sacral segments with vertebral bodies anterior to the
spinal cord and the spinous processes posterior to the spinal cord. And importantly,
we see the end of the spinal cord typically in adults around the L1 to L2 area which is
called the conus medullaris, that end of the spinal cord, and from there the spinal cord
gives rise to the cauda equina where those horsetail of peripheral nerves that descend
in the vertebral bodies and exit out into the legs. And we can see pathology affecting
the spinal cord proper from the upper cervical region C1 down to the upper lumbar
region L1-2, and then we can see central nervous system pathology give rise to
peripheral nervous system disorders by affecting the cauda equina. And those would
be lesions in the lower lumbar space L2, 3, 4, and then down in the sacrum. So we're
dealing with the spinal cord, we're dealing with the central nervous system, but within
the vertebral bodies and the vertebral apparatus we have both central and peripheral
nodes. Let's look at one segment, a representative segment of the spinal cord.
When we think about the spinal cord, we divide it into each individual segment and
here you can see one schematically depicted. In each segment of the spinal cord,
we have a ventral portion and a dorsal portion. The ventral portion of the spinal cord
gives rise to the ventral nerve roots and there we see the fibers for the motor nerves
that descend out from that segment of the spinal cord. And correspondingly, the dorsal
nerve roots carry sensory information in from that segment of the body, that dermatome
of the body. Those cells bodies arise and leave in the dorsal root ganglion and then travel
in to the spinal cord where they either synapse or cross over to the opposite side of the
spinal cord before ascending to the brainstem. We can also think about and look at the
spinal cord topographically and here we're looking at a typical segment from top down
and there are a number of important layers and areas of the spinal cord that will
present differently. First, we see the spinal nerves inside the canal, the spinal cord
proper. Just outside of the spinal cord is the subarachnoid space and that's very
important. We need to see that space on MRI scans to know that there is
non-compression or pathology that is affecting the spinal cord. Within the subarachnoid
space, we see the nerve roots, the dorsal and ventral nerve roots as they exit or
enter the spinal cord. Just lateral to those are the dorsal root ganglion which actually lie
within the neural foramen, the foramen through which the nerves exit and are susceptible
and sensitive to compression in that area. Then we have the dura which surrounds the
dorsal root ganglia and then following that and outside of that is the epidural space
and we can see pathology affecting the epidural space and compressing inwards
to the spinal cord resulting in pathology. So when we think about the spinal cord,
we can divide it into each of those areas and that can help us to understand typical
clinical presentations for patients. The first location or place within the spinal cord we
think about is the spinal cord proper, the nerves themselves. There is gray matter nuclei
and white matter tracts. And certain pathology will affect the gray matter nuclei, things
like strokes in the spinal cord or toxic metabolic problems within the spinal cord. There is
also certain pathology that will affect the white matter tracts. In certain degenerative
conditions as well as compressive lesions and various inflammatory or infectious
processes can affect the white matter or gray matter. The second area within the
spinal cord is the arteriovenous system. And we have arteries and in particular the
anterior spinal artery will be very important for patient presentations from vascular
problems affecting the spinal cord and the epidural venous plexus, that plexus around
the spinal cord and the epidural space. And metastasis or infections, osteomyelitis,
and others can affect the epidural space and present with a problem compressing the
cord externally. The third area or region within the spinal cord are the vertebral
bodies. Around the vertebral bodies we have anterior and posterior ligaments which
can be susceptible to trauma or can affect the location of herniated disc or other
degenerative pathology. We can see thickening of those ligaments compressing the
spinal cord and causing myelopathic presentations. There is also the intervertebral
disc material and in patients with degenerative disease or degeneration arthritis of the
spinal cord, that disc can protrude and result in compression of the spinal cord contributing
to patient's symptoms. And then the last area of the spinal cord and spinal region
are the peripheral nerves, and that's that cauda equina, peripheral nerve that live
inside the central nervous system and can be susceptible to pathology that that can
present rather suddenly and should be on a clinician's differential diagnosis for some in
many of these patients.