so spinal segments and spinal nerves some of them are a little more complicated than others so
in general this diagram kind of represents what we talked about in the previous segment where
you have a spinal segment one spinal nerve and it comes out and distributes this is a diagram
of its distribution on your body surface okay and so what you can see from this is that your
spinal segments overlap and that's a good thing so most of them are pretty simple these would
represent things in your thorax for example your what we call your intercostal nerves they come out
they run around the edge of the rib and then you know give off little branches to your sides and
then to your to your anterior chest there are of though areas of the body where the spinal nerves
exit they come together to form this great big net and then they but then again once they hit
the surface they distribute evenly just like the simple ones so some of them are simple like your
intercostal nerves and some are more complex and they form plexuses and we'll talk about
the plexuses and a separate lecture called spinal peripheral nerves - so with regard to your spinal
nerves you have 31 pairs and these include eight cervical 12 thoracic five lumbar five sacral and
one coccygeal so those you so you have 31 pairs of spinal nerves you have 31 spinal segments and
you'd say well dr. Sullivan I only have seven cervical vertebra how can I have eight cervical
nerves so you have 31 pairs of spinal nerves 31 spinal segments 8 cervical 12 thoracic five
lumbar five sacral and one coccygeal where this starts to not make it a little where this starts
to get maybe a little confusing is that you have seven cervical vertebra but eight cervical nerves
this is because see one egg it's over the top of the first cervical vertebra right underneath
the skull base and right over the c1 vertebra so c1 through c8 exit over the vertebral body
t1 all the way down through s are going to exit under the vertebral body okay so t1 exits below
the t1 vertebra okay so all the way from c1 over over over over till we get to c8 which
entered which exits under C7 and then t1 over under t1 all the way down to the sacrals
so I hope that makes sense the spinal cord ends at approximately l1 to l2 because as we
discussed earlier when you're an infant your spinal cord is about the same length as your
vertebral column but as you grow the cord grows much more slowly than the vertebra and so it the
result is that the nerves still exit make their appropriate exits which results in this cauda
equina this big horse tail bundle of spinal nerves the significance of this is when you
if you're sick enough hopefully you never are to need a lumbar puncture this is this makes it
really convenient so what I want you to do is put your fingers on your iliac crest move your
thumbs then straight back and you're at about l4 so if you enter the spinal column or the vertebral
column at around l4 you notice that the needle is going to go in and there's no spinal cord to
hit this is really good because you can puncture and draw spinal cerebral spinal fluid from within
the dura at this point and the needle because of the pressure have you ever tried to put a fork in
and just poke a spaghetti noodle in the water it doesn't work very well the it just squishes out
of the way that's basically what happens with the cauda equina when you push in a needle to
to do a spinal tap the nerves move out of the way you're able to get a sample of the cerebral
spinal fluid and then you don't add insult to injury by poking a hole in the actual spinal
cord itself in the next segment we'll talk in more detail about some of these spinal nerves