 Good day everybody. Dr. Sanjay Sanyal, Professor of Department Chair. So this is going to be a static dissection demonstration of the vertebral column, the back, the spinal cord, the spinal nerves, the spinal subacronyte space and a few points about the posterior costal space. So this is it ever and we spent quite a bit of time with the assistance of my students to dissect out the suboxibital region. We have excised the occipital bone, the squamous part of the occipital bone. In effect, we have done a posterior fossa crinectomy and we have opened out the posterior cranial fossa and we can see the two cerebellar hemispheres. Then we continued the incision down. We had to remove the paraspinal muscles here and on this side. The paraspinal muscles being the outermost layer, the erythrospinae muscles composed of the heliocostalis, lungismus and the spinalis and the deep muscles namely the transversal spinalis. We also had to cut the lamina of the vertebral column all the way from the cervical region to the sacral region. So in other words, we had to do a laminectomy and then we had to split over the dura and you can see the upper portion of the dura has been split and what you can see inside is the spinal cord. So this process is an extensive process. It took almost one week. Six students were working almost continuously and it's not something which we can do on a daily basis. And the next slide shows the further continuation of the opening of the dura. What we see essentially here, this is the spinal subarachnoid space and inside the spinal subarachnoid space we can see this spinal cord. This spinal subarachnoid space is filled with CSF in life. In a cadaver we cannot see the CSF because it has been drained away. And we can see that this is the combined dura and the arachnoid. We just should show you more clearly in the next view. So this is an enlarged view of the same thing shown transversely and we can see the cut margin of the dura arachnoid. The inner smooth whitish structure is the arachnoid. It is composed of flat mesothelial cells and the outer portion is the dura which is tough leathery and membranous. So this is the dura border cells are closely adhering to the mesothelial cells and constituting what is known as the dura arachnoid interface. This shiny translucent membrane that is covering the surface of the back of the spinal cord this is actually the biometer embedded within the biometer we have these plexus that we can see here. This is the plexus of lascular structures. More precisely on the posterior aspect we have two spinal arteries, posterior spinal arteries both of them come out from the vertical artery. So this is one posterior spinal artery that we can see faintly here and this is the other posterior spinal artery which we can see. The posterior spinal arteries they descend down typically just medial to the attachment of the spinal nerve roots which I shall mention just a little while later. These posterior spinal arteries they are supposed to be deficient in the region of T1 to T3. This is actually the thoracic segment of the spinal cord that we are showing right now and they have to be reinforced by means of the segmental medullary arteries which enter the vertebral canal through the intervertebral foramen from outside and therefore they form a plexus and that is the plexus that we can see here. So if for some reason in this region we have occlusion of the posterior segmental medullary arteries and the T1 spinal arteries are also weak then we can get ischemia of the T1 to T3 segment of the spinal cord what is referred to as the posterior spinal artery syndrome. Posterior spinal artery supplies the posterior one-third of the spinal cord specifically the dorsal columns and the roots the dorsal nerve roots. So this is a static image showing the distribution of PSA and therefore the effect of occlusion of the posterior spinal artery. Posteriorly we also have three spinal veins, longitudinal spinal veins and we can faintly see them here one of them is this one, one of them will be the middle line and one of them is this one here. The three posterior spinal veins they ultimately they range to the intervertebral veins and they range out. They also communicate with the internal vertebral venous plexus which is situated outside the dura but they are not present here this is the spinal subarachnoid space. Now let's focus on this spinal nerve roots that we can see here. The roots of the spinal nerves they do not arise by a single nerve fiber as we can clearly see they arise by means of multiple branches these are referred to as the root lengths of the spinal nerves. So if this was let's say for the sake of discussion this was the T3 spinal nerve then these are the root lengths of the T3 spinal nerve and this segment of the spinal cord will be referred to as the T3 spinal segment or whatever. So that's how we count the spinal segments because as such there is no other indication on the back of the spinal cord or the front for that matter which indicates the spinal segments except the attachment of the rootlets of the spinal nerve. So therefore we can see the rootlets here we can see the multiple rootlets here we can see the rootlets here and here and so on and so forth. Now let's come and see how the spinal nerves emerge. When the spinal nerves are emerging they pierce through the dura arachnoid. So therefore the inner surface is the arachnoid as I mentioned earlier and also surfaces the dura. This is the small portion of the spinal nerves which are inside the subarachnoid space and here they're they're paced by CSF. This provides a small area for drainage of CSF by means of the perineural lymphatics. So apart from the usual drainage of CSF these small portions drain through the lymphatics around the spinal nerves. Then these spinal nerves they pierce through the dura arachnoid and in so do we the dura arachnoid and also the pyra as a matter of fact they all merge with the epineurium of the spinal nerves and we can see that much more clearly in this view here. Once the spinal nerves pierce as I said we are in the thoracic region the back of the thoracic region they become known as the intercostal nerves and we can see one intercostal nerve here we can see another intercostal nerve here. These intercostal nerves initially they run in the endothoracic fascia and we can see they're accompanied by the vessel cells. Typically the vein is on the top the artery is below and the nerve is in the lower most vein artery nerve. They run in the coastal groove on the under surface of the rib above and here they have been displaced down a little bit. So this is the orientation and as they go further they enter into the intercostal muscles between layers two and three. Layer two being the internal intercostal muscle and the layer three being the innermost intercostal. In this particular region this is the region of the angle of the ribs which was attached by the erector spinal muscle. So therefore in this region the innermost intercostal is called the subcostal muscle. So therefore it runs between the subcostal muscle on the inner surface and the internal intercostal muscle and then they continue and when they continue they also give the collateral branches. This is a transverse MRI through the thorax to show the course of the intercostal nerves which we just described. Since we are also on the back of the chest I will use this occasion to mention a few quick words about thoracotomy, postural lateral thoracotomy. When we are doing a postural lateral thoracotomy we don't go through the intercostal space. We make an incision on the surface of the rib and that incision is made like this on the surface of the rib and then we split the periosteum above and the periosteum below and then we reflect the periosteum and then we shell out the rib from inside by means of a rib cutter. By so doing we have the added advantage of getting the space above and the space below. So therefore it gives a wider exposure. Subsequently when we close the periosteum osteogenic layer of the periosteum allows the rib to grow back and by doing this procedure we also avoid damage to the intercostal neurovascular structures both above and below. So this is the approach to postural lateral thoracotomy. So these are the points which I wanted to mention to you about the spinal subarachnoid space, the CSF, the spinal nerves, the biometer duroarachnoid and the posterior spinal artery and the vein and the plexus and the posterior spinal artery syndrome. Do stay tuned for the next section of this video where we shall go further down in the same section and mention the lumbar cistern, the cauda equina syndrome and we will also go right up and mention something about the junction between the medulla and the spinal cord. Thank you very much for watching. Dr. Sanjay Sanyar signing out. If you have any questions or comments please put them in the comment section below. Have a nice day.