Nerves. There are so many things that get on mine. Coleagues. Family. Too many people. Absence of people. Loud noises. Quite noises. Silence.

I do occasionaly wonder how the phrase “It is getting on my nerves” came about, but I never bothered to look.

©Charly, all rights reserved. Click for full size.

What you see here is in no way detailed depiction of peripheral nerves, only a rough outline of some main plexuses. What is ingenuous about nerves is the way they are led though holes and around various joints in a way to avoid pinching, squeezing or bending at a sharp angle. Everyone who has ever hit their elbow in between the protrusions on ulna where the nervus ulnaris leads knows what irritated never means – pain. Lots of it. This brings a memory of Caine, and not a happy one at that. She had an inflammation of nervus ischidadicus and if you ever have difficulty to imagine how that feels like, hit yourself in the elbow and multiply the sensation by about four times and prolong it indefinitely. I have already mentioned when talking about the pelvis that this pain can be so extreme as to lead someone to suicide.

But on a cheerier note, plexus brachialis is a cluster of nerves near surface around the musculus trapezius. That is where you have to squeeze in order to apply the vulcan nerve pinch to render your foes unconscious.

Of course vulcan nerve pinch does not work for non-vulcans, but should you ever find yourself in a self-defense situation, knowing where nerves lead near surface is indeed useful, since irritating nerves elicits involuntary reactions in even the strongest individuals. If you ever find yourself in a situation like that, my recommendation is to use thus gained fraction of a second to get the hell away.

We looked at our heart, but not at all the piping connected to it. There is rather a lot of it and this picture shows only a very, very small part.

There will be talk about testicles, read at your peril.

©Charly, all rights reserved. Click for full size.

Whilst the air pipes in the lungs are optimized for keeping constant pressure, for veins and arteries this is not the case. Perhaps there is less selective pressure for optimisation, or it is not possible to achieve? I do not know. The truth is however that there are a number of sub-optimal divisions and loops and one of them is so peculiar that once you learn about it, you will not forget it.

Professor Kos explained to us, that one such badly optimised division is at least in part responsible for the fact that one testicle is usually lower than the other, and the one that is lower is usually the left one. When you look at the picture at the right side and follow the vena cava inferior down from the heart past venae hepaticae you will come to a cross junction where from it split two venae renalis. And looking further down you will find out that venae testicularis do not both split of from the vena cava inferior symmetrically, but vena testicularis sinistra splits of from venna renalis at a near right angle. That is bad engineering – right angles mean loss of pressure automatically.

However when looking at the left side, where arteries are depicted, both arteriae testicularis split symmetrically and directly from arteria abdominalis at an angle in the direction of the blood flow.

This means that whilst fresh blood supply for both testicles through arteries is about equal, the outflow via veins is not. That means different blood flow rates through the testicles, leading to their different sizes and also different position. Because testicles regulate their temperature (which has to be lower than body temperature) via positioning, and this way the left testicle has to hang lower in order to keep the same temperature as the right one.