So now let's look at the
various spinal cord segments.
You'll notice that the segments
can vary by size, shape
and amounts in distributions
of gray and white matter.
Each spinal cord segment
refers to the part of the vertebrae
where the spinal nerve exits
from the intervertebral foramina.
You'll notice that the white matter
begins to decrease as you descend
from the cervical portion
to the sacral portion.
This is because of two main reasons.
As you ascend, you are going
to add more sensory tracts
and as you descend,
you have less motor tracts.
You will also notice that the cervical and
lumbar have the largest amount of grey matter.
This is because they are
responsible for innervating the limbs.
So now let's take a closer
look at each of the segments.
So first we start with the most
superior or the cervical segment.
This segment has a relatively large diameter
and has a large amount of white matter.
It is also in an oval shape.
The upper cervical segments
have a large posterior grey horn
and a relatively small anterior grey horn.
The lower cervical segments for C5 and below,
which looks like what is depicted here
have an enlarged posterior grey horn and as well
as an anterior grey horn that is well developed.
The next spinal cord segment
is the thoracic segment.
The diameter of this segment is a bit
smaller than that of the cervical segment
and this is due to its relatively
small amount of grey matter.
Except for the first thoracic segment, it also has a
relatively small anterior and posterior grey horn
and also contains a small lateral grey horn.
The third segment of the spinal cord
is going to be our lumbar segment.
This segment is nearly circular, it contains a
very large anterior and posterior grey horn
and as well, it has a small lateral
grey horn in the upper segments.
There's relatively less white matter
than that of the cervical segments,
again for the reasons I mentioned before.
The next segment is the sacral.
The sacral spinal cord
segment is relatively small
but it actually has a pretty
large amount of grey matter.
Again, the amount of white
matter is also very small
and it contains large and thick
anterior and posterior grey horns.
The final spinal cord segment
or the coccygeal segment
resembles the lower sacral spinal
It is just much smaller.