Thanks for all the answers!
@IanB
How does electric shock at low-voltages affect the brain? Anything the worry about?
Which internal injuries are you referring to? Like if the burn occurred in a finger.
If you have to ask, maybe it's already done its job...
J/K.
Internal injuries are more like... oh, you got ten amperes through your meat or veins? Let's destroy some tissue.
Food for thought (literally);
http://youtu.be/aUAkezGstlQSimply, if there's enough raw power delivered to cause temperature rise and internal injuries (burns, tissue destruction, later necrosis, and maybe worse things), you get secondary problems from that.
The most prominent immediate hazard is electrical disruption of the heart. Burns are what happens when that doesn't (or isn't enough), or when your muscles contract and you get stuck. Electrical disruption of the brain, I think, is a very low incidence thing; if you've ever seen electroshock therapy hardware, it looks pretty robust... the scalp isn't very conductive (because of the skull and dura mater, and maybe simply because... the brain is mostly greasy compounds, so maybe isn't all that conductive unless you get into the arteries?), so it's fairly powerful, considering that it ultimately doesn't have to do very much, electrically speaking.
Also, I don't think normal people are at much risk of anything electric in nature (besides heart problems, as I said). If you're prone to seizures, that might be a risk factor and hazard for working on wires near your head or neck. Other than that, no, I don't think the cranial risk is there.
Tim