In The Walking Dead (TV), how do zombies walk without blood circulating?

In The Walking Dead (and most zombie movies), the zombies reanimate and then are able to walk again, eat again, and see again without respect to any injuries the person received before "dying." How does a reanimated being walk if the heart or certain muscles is destroyed? Clearly in many shots of the zombies we see little if any blood from the zombies. In the early part of the series, we would see half-stumps of people, dead people with large chest wounds, or dead people with partially eaten, injured or decomposed muscles that attempt to get Rick or other survivors.

What is evident is that circulation is not happening or possible in many cases. In living creatures, circulation of blood is what keeps motion possible. We know from having a foot or other limb "go to sleep" that we cannot move that limb until we get circulation back. Does the brain and nervous system become strong enough to "shock" the body into moving? how does that sustain without circulation? what happens then if the spine was severed?

Thanks for going on this trip with me!

Answer

One explanation (not specific to The Walking Dead) that I've seen offered is that not all circulation ends. Instead, it is only portions of the circulatory system that shut down (capillary and smaller veins and arteries).

Only the most essential main arterial paths remain in place, providing only enough circulation to handle a degraded level of gross motor function (providing a bit of a hand-wavy explanation for the stereotypical shambling gait and generally clumsy movements).

This also explains the atrophy of flesh, as the shut-down of the capillary system prevents sufficient flow of oxygen to skin tissue to keep it alive.

Perhaps a Walker with a destroyed heart would lose motor function, but this would likely take a bit of time for it to register with the limbs. I don't recall any direct and clear heart shots from the show, so I'm not sure if this theory is verifiable one way or another.

The Walker's movement still relies upon direct impulses from the brain, so severing the spine would stop all motion reliant upon connections below the point of separation. This is why direct brain trauma "kills" a walker, but decapitation leaves the head still "alive".

Of course, that also raises the question of how motor function is possible in a severed head, since clearly no circulatory system would be functional. The best hand-wavy answer I can come up with here is that the brain, being apparently the central source of the infection (if you remember from their time in the CDC center, we saw a recording of how the virus "activates" throughout the brain upon death), the virus can exert direct control over nervous system functions and also directly sustain tissue without need for oxygen delivery via blood steam.