So now that we've discussed
the different spinal cord segments,
let's talk about the spinal nerves.
The spinal nerves are what
connects the central nervous system
to the sensory receptors,
muscles and glands of the body.
The spinal nerves are considered a
part of the peripheral nervous system.
There are 31 pairs of spinal nerves.
And the anterior and posterior roots attach a
spinal nerve to a segment of the spinal cord.
If we take a closer look at the
individual parts of the spinal nerves,
you will find that there are
8 pairs of cervical nerves,
12 pairs of thoracic nerves,
5 pairs of lumbar nerves,
5 pairs of sacral nerves
and one pair of coccygeal nerves.
Recall these different names
correspond to the vertebrae
where the spinal nerves will
exit from intervertebral foramina.
So if we take a closer look at
the anatomy of the spinal nerves,
starting with the connective
tissue layers that cover them,
you will find that there are three
main connective tissue layers.
First, you have the epineurium which
is going to surround the entire nerve.
Inside, we have bundles of
axons referred to as fascicles.
The connective tissue layer covering the
fascicles is referred to as the perineurium.
And then finally, each individual axon contains a
connective tissue covering called the endoneurium.
And together, this transverse section
shows the coverings of the spinal nerve.
So along with the spinal nerves as they
exit from the intervertebral foramen,
the spinal nerve is going to divide
into several brances known as rami.
There's the dorsal rami which is going
to serve the dorsal portion of the trunk
and goes toward the posterior
portion of the body.
Then you have the ventral
ramus which is going to serve
the ventral portion or anterior portion of
the trunk, and the upper and lower limbs.
You also have meningeal branches.
These branches from the spinal
nerves go from the spinal nerve
and then re-enter back to the spinal
cord through the intervertebral foramen.
These supply the vertebrae, the vertebral ligaments,
blood vessels at the spinal cord and the meninges.
And then finally, for the autonomic nervous
system, we have the rami communicantes.
These are going to contain
our autonomic nerves.