But it is only the nerves and crebral cortex that animate the dead- much like applying an external electric current can cause a dead limb to move. For digestion, nutrient absorbtion, thermogenesis etc to be functioning, their would have to be cardiovascular and lung function- technicaly defining the zombie as alive. This works fine if they are in fact living humans suffering from a virus (28 days later), but a 'proper' undead zombie, has no such active physiology. Indeed, according to 'Romero's Law' first established in the late 60's, a zombies main enemy is time. Whilst decomp of the organs begins quickly, the muscle tissue and nervous system survives in tact for longer, allowing basic motor function to occur. inevitably though, when the muscle tissue fails, no matter what basic brain function remains, no limbs will be able to react to the messages sent to it. once decomp renders them unable to move, the threat is over.
on this basis, a dead body, exposed to the air and elements should have a mobility span of no more than 4-6 months. It is doubtful during that period that any increase in brain function would occur, and so the ability to learn (a theory recently considered by my esteemed colleague Dr. Romero), would seem unlikely.

Interesting. So we can assume that cell division has stopped. This would prevent the zombie from "healing" to any great extent. The zombie virus must keep the cells in a semi-suspended state of activity, where they can act as normal cells do, with a much longer (single phase) life span than a normal cell - but still with eventual necrosis.

I am unclear on the muscle cells mytochondrial/ATP functions. Something must still be causing the zombie muscle to react to the electrical stimulus. Whither BuDoc or srv?

"In case you ever wondered what it's like to be knocked out, it's like waking up from a nightmare only to discover it wasn't a dream." -Forrest Griffin