Why to people keep quoting Max Brooks (The Zombie Survival Guide) over and over again about How do Zombies function after death - according to Max the virus basically rewires whats left of the brain, and continues to send electrical impulses to the tissue after death. The bodies systems are preserved so well because the virus kills all other bacteria - meaning that decomposition does not proceed at a normal pace.
Max's spurious waffling's are based on a total lack of understanding how a nervous system works. He started his Zombie survival seminars as a gag originally anyway, so I just can't take his thoughts that seriously. Maybe if he had majored in medicine rather than History - I might lend his ramblings more credence.
When a nervous system actually dies, it is utterly incapable of generating or transmitting electrical impulses of any kind. Period - that's a fact of life (death) you can't change that - even the Zombie virus couldn't change this, especially considering a virus can only actually effect living tissue. A Virus can lie dormant in dead tissue for decades, but that's about it.
The only way it could work in that example would be if the subject wasn't actually dead - and then they aren't really Zombies anymore.
What if the Virus somehow changed the way living tissue actually worked BEFORE the Host finally died - like healthy tissue becoming cancerous tissue - cancer cells grow and divide at an unregulated, quickened pace. As the cancer-like (Z-Cells?) cells grow/reproduce/replace the healthy living tissue - the victim falls ill while the process takes place. That would also explain the difference in time it takes to effect a victim, some are fast others take a while - it would depend on the overall health and strength of immune system.
As the Z-Cells are really quite different from the healthy cells of the original host, it would also explain a number of things.
1 - This is why the rotting slows (and often stops) - only the remaining normal cells would decay, this would leave the emaciated walking corpses we know and love.
2 - This is why Zeds crave human flesh, as their bodies are somehow craving what they have lost on a genetic level, healthy Human tissue.
3 - As the brain of the victim has been replaced with Z-Cells, one can assume that the brain is now working on a much simpler level. It would appear mostly dead to examination, but still functions on a rudimentary level - which is why destroying the brain kills the Zed.
4 - As the bones and muscles are now Z-Cells, that don't require blood flow or oxygen to work - it would explain why Zombies are slow and shambling. Only really fresh Zombies (those still with original cells present) would be able to move at any great pace.