Tutorial 41: distinguishing nerves and arteries in dissection

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I whipped up these doodles with a handwritten list of characteristics during office hours recently, and then realized that this should be a tutorial post.

 

Most of the stuff listed in the image is pretty self-explanatory, but I want to expand a bit on the textures. Nerves are bundles of axons, bound together in sheets of connective tissue. As you follow nerves outward, from the central nervous system toward the axon targets or receptive nerve endings, they will branch and branch, again and again, down to the level of individual axons. So although the axons themselves are too small to see in a gross dissection, the collected bundles of axons inside each nerve often give nerves a striated texture. 

 

In contrast, arteries are hollow muscular tubes that carry blood, and they look like hollow muscular tubes. A weird and IMHO under-appreciated fact is that arteries can’t be nourished directly by the blood that they carry; their walls are too thick. So they have tiny vessels in and on their walls, called vasa vasorum, or “vessels of the vessels”. The vasa vasorum are hair-fine when they are visible at all, and they squiggle just like macro-scale arteries, so texturally arteries often look vaguely hairy, with fine reddish threads winding across their surfaces.

 

In practice, though, the directness of the course — or lack thereof — and branching pattern is usually enough to make the call. Basically, nerves do not have time for your crap. They are hell-bent on getting where they are going with a minimum of farting around. In contrast, arteries never travel in straight lines if they can avoid it. They’re always throwing in a saucy swoop or curve, for no other reason than because it looked fun.

 

Why haven’t I talked about veins? By rights I should, since arteries usually travel with veins, and complete neurovascular bundles — each consisting of a nerve, an artery, and a vein — are common in vertebrate bodies. But in my experience students are almost never confused about the difference between arteries and veins. But for the sake of completeness, veins tend to be dark-colored in embalmed bodies, because they don’t completely empty of blood, and they are visibly thin-walled and floppy. Because veins are thin-walled, if they do empty out they can also flatten out, and look wider than the neighboring arteries. On the other hand, it’s not unusual to see a bifurcated vein, with one branch running on either side of the corresponding artery.

 

A couple of caveats about all of the above: