Anatomy of the Spinal Cord (Nursing)

00:01 Now, let's take a closer look at the spinal cord and the peripheral nervous system or PNS.

00:08 Here, we have a typical cross-section of the spinal cord.

00:12 The arrangement of gray and white mater is somewhat the opposite of what we see in the brain and that the gray matter of the spinal cord tends to be more deep or inside and the outside portion is going to be mostly the white matter.

00:28 Again, the gray matter represents where cell bodies and nuclei are and the white matter, where myelin of axons is going to be located.

00:38 We also find in the middle a very small opening called the central canal.

00:44 And this is where cerebrospinal fluid flows and this is the equivalent of ventricles in the brain.

00:53 We also have the same type of meninges that we saw in the brain starting with the pia mater which is directly attached to the surface of the spinal cord.

01:03 Then, the arachnoid. And between the arachnoid and pia mater, we still have subarachnoid space and just as with the brain, the subarachnoid space is also going to be filled with cerebrospinal fluid.

01:19 Then, finally, the outermost layer of meninges, the strongest layer is the dura mater.

01:26 And all along the course of the spinal cord, there will be spinal nerves exiting out the spinal cord through the vertebral column to branch into all of the peripheral nervous system.

01:40 The spinal cord doesn't actually run all the way down the length of the vertebral column though.

01:47 As you can see here, it actually starts to end early on into the lumbar area, so, that by the time you get to the L2 or L3, L4 area, it's really just a collection of individual nerves rather than a solid cord and it gets the name cauda equina because it looks like a horse's tail and that's essentially what cauda equina means.

02:13 This is pretty useful when it comes to the process of carrying out a lumbar puncture.

02:19 Because sometimes, there are indications for sampling cerebrospinal fluid and sampling it from the brain is for the most part impossible or dangerous and getting it from the spinal cord can be difficult if you're going to hit the actual spinal cord itself.

02:37 So, knowing that the spinal cord ends in the cauda equina at the very distal end, we can target that area when we take a lumbar puncture.

02:47 By locating the appropriate lumbar vertebra and taking a posterior approach through the dura, through the arachnoid into the subarachnoid space where the CSF is, not only can we have relatively easy access compared to other parts of the body, but we don't have to worry about damaging the spinal cord because it's ended a few levels up higher from here.

03:16 Here, we're going to look at the various parts of the spinal cord which correspond to the overlying vertebral body, very similar to the way lobes of the cerebrum corresponded to the overlying skull bones.

03:30 So, in the area of the cervical vertebra, we have the cervical part.

03:34 In the area of the thoracic vertebra, we have the thoracic part.

03:40 Similarly, we have lumbar nerves in the area of the lumbar spine.

03:48 And then, by the time we get to the sacral area, they are, of course, just individual nerves.

03:53 It's not really the spinal cord anymore but we have sacral nerves in the area of the sacrum.

04:00 And then, there's a single coccygeal nerve down by the area of the coccyx which is the smallest, most terminal portion of the vertebral column. Here's something that will help exemplify the concept of spinal nerves hopefully, pretty well. And it's the idea of a dermatome.

04:19 A dermatome refers to a region of skin whose sensation is supplied by a particular spinal nerve.

04:27 And so here, we can see in a map form of sorts, the dermatomes provided by the cervical spinal nerves.

04:36 So, we know that if there's any loss of sensation in this area in red, it can be traced to some sort of nerves supplying one of the areas of the cervical spinal cord.

04:49 Similarly, here, we have the thoracic dermatomes. So, we see the areas innervated by thoracic spinal nerves.

04:58 Then, we see the lumbar spinal nerves and the sacral and coccygeal nerves.

05:06 Dermatomes have a lot of clinical significance beyond just testing for sensory deficits.

05:12 For example, there's something called shingles which is a virus that's actually a reactivation of a virus that lives inside, usually, for a long time of a nerve.

05:26 It can be dormant inside of this nerve without any symptoms until it's reactivated as shingles and when it does so, because it's inside a given nerve, it will outline the area of a dermatome for you.

05:40 So, for example, here's an example of shingles along a thoracic dermatome.

05:45 So, the distribution of this rash just by looking at it because it's this particular strip of skin tells you it's along a thoracic dermatome and it tells you that that virus was hiding inside one of the thoracic spinal nerves.

06:01 This also relates to something called referred pain.

06:05 And referred pain is something that is pretty common in certain pathologies.

06:12 So, with all of these nerves supplying a dermatome, they're all coming back to a particular spinal level.

06:21 But there are other things coming back via spinal nerves and other types of nerves to that particular spinal level as well.

06:32 For example, the skin of, for example, maybe the area of the shoulder, might be going back to this portion of the spinal cord.

06:43 But that level of the spinal cord may also be receiving sensory input from the heart.

06:51 And if there is, for example, a heart attack, that sensory information from the heart coming into the same level as the sensory information of skin from the shoulder might get confused and you might get what's called referred pain.

07:05 Whereas the pain maybe since is coming from the skin of the shoulder when it's really coming from the heart.

07:12 And that's why it's important to know about referred pain because sometimes, referred pain may be indicating something more serious.

07:21 And for example, here's a map of some of the areas on the skin where pain may be referred from organs that you might not expect based off of their anatomic location.

07:32 And again, that all has to do with the fact that the nerves from both that patch of skin and the organ that's referring pain to that area are going back to the same spinal level.