Pleural membranes. The pleural membranes are found lining the lungs, and to understand them, let's take a look at some of the anatomy in this cross-section, where in color we can see the external intercostal red, internal intercostal in yellow, and then the innermost intercostal there in blue, and then we see the ribs there that are kind of in a brown color, and they surround where these pleural membranes are just internally, that there are serous membranes that help surround the lungs and to have fluid to help them to move without friction. Of course, those surround the lungs and the lungs receive and take away air via the bronchial tree.
There's the bifurcation of the carina into the right and left primary bronchi. So the pleural membranes that are surrounding the lungs are like two plates of glass and a drop of water. So there are two plates of glass and here's a drop of water in the middle. And so as those two plates of glass come together and they touch the water and then squish together, they now have, through hydrostatic pressure, stay vacuumed or suctioned together, so now they don't pull apart.
However, you can still move them around, and so this is very similar to what happens with regards to the parietal pleura, the layer that lines the internal surface of the ribs and internal intercostal, and the visceral pleura, the mesothelium that lines the external surface of the lung, where the parietal pleura and visceral pleura can move upon themselves, but they stay vacuum sealed together, thus reducing friction, and yet allow them to still move. So the parietal pleura that's outlined on the right lung in this oblique view, in the step dissection, everything in blue is parietal pleura. Now anatomists have gone...
to the extent of naming the different parts of parietal pleura. And so the part of the parietal pleura that lines the internal surface of the ribs we call costal parietal pleura. The part of the parietal pleura that lines the top dome of the diaphragm, diaphragmatic parietal pleura.
The part that lines where the mediastinum is located by the heart, that's mediastinal parietal pleura, flanking that side of the heart. And then the part that projects up into the neck they call cervical parietal pleura. All of its parietal pleura, mesothelium, just naming where it's located. Visceral pleura that's in red is what's found intimately associated with the outside parenchyma of the lung. This is the part that's part of the lung.
And the pleural space is the space between the parietal pleura and visceral pleura. The root of the lung, that's where the visceral and parietal pleura come together, where the bronchial tree and pulmonary vessels. enter into and exit the lung.
The costodiaphragmatic recess is an interesting thing because there in yellow, we just take a section of the bottom of that lung on the right, we blow it up, and the costodiaphragmatic recess is an area where there's a double membrane of parietal pleura, and in that area, and It's doubled upon itself and it leaves a space. Now this is significant because when you inhale, your lungs expand. And notice that the tip of the lung goes and fills that costodiaphragmatic recess.
And then you exhale. Inhale, it fills it. Exhale, it then leaves that little recess. It's called costodiaphragmatic recess because costo for ribs, diaphragm, it's that recess between the ribs and the diaphragm.
Let's talk about the innervation of these pleural membranes. So first the parotid pleura that we see outlined in turquoise in this picture, and another cross-section through the chest, and showing in turquoise there where the parotid pleura would be lined. It's the ventral ramus that is really an intercostal nerve that courses around through that body wall between the innermost and internal layer of the intercostal muscles. They send off these tiny...
twig branches that are sensory all along the parietal pleura. So it's the intercostal nerves that are providing innervation of parietal pleura. Intercostal nerves are somatically derived, so this is including pain, temperature, touch.
Now the visceral pleura that's more there in lime green, that's, oh, sorry, parietal pleura as well. Except parietal pleura, we haven't discussed the mediastinal or diaphragmatic parietal pleura. It also receives somatic innervation, but its innervation is via the phrenic nerve. that arises from C3, C4, and C5 spinal cord levels. So that's what provides somatic innervation of pain temperature touch to the mediastinal and diaphragmatic parietal pleura.
Now our visceral pleura, This one receives innervation, but because it's associated with the viscera itself, this is sensory autonomic, but it's visceral sensory, where that information travels, visceral afferent neurons travel along sympathetic pathways, and notice that it goes into the dorsal root. And then we also have visceral afferent neurons going along parasympathetic neurons, going back to the medulla. This information is things such as stretching of the smooth muscle, change in the diameter of the airways, damage to the tissues, things of that nature.
And that's innervation of the pleural membranes.