Sefner said:
This is what happens in chickens. They are not conscious of this. The best way to explain it is that the last thing the brain knows is panic and thus tries to flee. So that's what it's doing when the head is severed. If part of the brain remains, it is still acting under its last signal of panic.
Umm... not exactly.
There's no need to invoke the emotional state of the chicken to explain this.
It's not a matter of the last thing the chicken "knows" or "feels." It's a matter of what motor reflexes are present at the level of the spinal cord vs. higher levels of the central nervous system. In an intact nervous system, those spinal reflexes are
inhibited by input from higher levels. So when the chicken's spinal cord is severed, spinal motor reflexes, including some reflexive locomotion, are disinhibited -- and the chicken may run a few steps. (Locomotion in birds is more stereotyped than in mammals... more of a reflex thing. The chicken either walks or it doesn't, pretty much. John Cleese, on the other hand, can do silly walks, which require more control at cortical and subcortical levels of the brain.)
When the doctor taps your knee, she's testing one of your spinal reflexes. One of the possible abnormalities is that the "knee-jerk" reflex is a lot stronger than it should be, which would mean that "circuit" isn't getting the right inhibitory signals from farther up, perhaps because your spinal cord is compressed at a higher level, or because something is amiss with one of the higher "centers" in the brain that does the inhibiting, and it's not sending out the right signals. Oversimplification, but that's the general idea.
But I have no clue about how Johnny Depp's nervous system works.
