The other day at work (Discipline of Physiology, University of Sydney), we needed an updated figure for one of our practical classes that we were moving over to a new online format.  The old image that we had I thought could have been portrayed a little bit better, and some of the terms used were a bit out of date:

So I volunteered to come up with an updated image.  These were the elements that I wanted in it:

I then adjusted a couple of things and added the base colour:
I then started added some detail and started cleaning up the image:

Next I added some shading and went in to do more of the detail. Since I am still learning the technique I learnt how to get the effects I was after as I went, so the first structure I painted (the spinal cord) looks different to the last one I did, the skeletal muscle:
Eventually I ran out of time and had to get the image finished so I exported the finished image into corel draw X7 and added all the labels, then exported the finished image:

I find that there are very few tutorials out there on scientific illustration. There are some but there are particular techniques that I have not quite grasped yet like how to blend the colour so that there is no need to add line work over the top of it to better delineate the structures as they do for comic illustrations where the black ink of the line work is a prominent part of the completed image.  What I am hoping to do is to pull together all the material I find that I used to learn scientific illustration, and to post it here so that it is all in one place.  Any techniques that are missing I will also track down and post them here too.