Welcome to this presentation on the spinal cord. The first thing that I want you to understand is that the spinal cord
is segmented. There are five segments associated with the spinal cord. First is the cervical segment. That is shown
in through here. The cervical segment has eight cervical levels associated with it, C1 through C8. This is one cervical
level more than the actual number of cervical vertebrae that we have in the vertebral column. The thoracic segment
is shown in through here. It is divided into T1 through T12 levels. The lumbar segment of the spinal cord is shown in
through here. It is then divided into five lumbar levels, L1 through L5. Sacral, more inferiorly or distally here is also
divided into five levels, S1 level through S5. Then lastly, we have the coccygeal spinal cord segment that is the
most inferior aspect of the spinal cord. Each of these spinal cord segments will give rise to pairs of spinal nerves.
A total of 31 pairs of spinal nerves will segmentally issue from the spinal cord. If we look at the cervical segment
of the spinal cord, there are eight cervical spinal nerves, one for each cervical level, C1, C2 all the way down to C8.
You can see each one of those cervical spinal nerves in the illustration. Again, there was one more spinal cord level
in the cervical area. There is C8 and this thing gives you one more cervical spinal nerve than there are cervical vertebrae.
It is important to note that all the cervical spinal nerves arise from above the corresponding vertebrae
except C8 which arises from below the C7 and similarly all other pairs arise from below the corresponding vertebrae after that
i.e. thoracic, lumbar, sacral and coccygeal.
The thoracic spinal cord segments, again they were divided into T1 all the way down to T12. Each level of the
thoracic segment of the spinal cord gives rise to a pair of thoracic spinal nerves. So we have 12 pairs of thoracic
spinal nerves. Then the number of spinal cord segments in the thoracic area as well as the number of thoracic
spinal nerves equals the number of thoracic vertebrae that we have in this segment of the vertebral column.
So here’s your first thoracic spinal nerve. Here’s the one on the opposite side and then T2, T3, and so on and so on
until you get down to the very last pair of thoracic spinal nerves, T12. The lumbar area had five spinal cord levels.
Again, each level giving rise to a pair of lumbar spinal nerves. Here we have five, L1, L2, L3, L4, and L5. The number
of spinal nerves will equal the number of lumbar vertebrae. The sacral segment of the spinal cord was divided into
five levels. Again, each one of those levels will give rise to a pair of sacral spinal nerves. Here we see S1, S2, S3, S4,
and then S5. The sacrum is the result of a fusion of five sacral vertebrae. So the number of sacral spinal nerves
equals the number of sacral vertebrae. Lastly, we had the coccygeal segment of the spinal cord, the most
inferior segment. It will give rise to one pair of coccygeal spinal nerves. Then we see those here and here.
So 31 pairs, when you add these all up, 8 plus 12 is 20, 25, 30, 31.