I think the automatic bladder has got to do something with cord transection above the sacral segments which supply the bladder and sphincter. When there is a cord transection, there is increased sympathetic activity below the lesion. I think this usually happens after the spinal shock starts to disappear. In the case of bladder, this increased sympathetic will close the internal sphincter and the bladder will keep filling. But since the sacral cords are intact, the neurogenic reflex will still be there. So, when the threshold is reached, reflex parasympathetic efferents will fire causing detrusor contraction and relaxation of the sphincter. You will be urinating like an infant.
With the autonomous bladder, your sacral segments are done for good. So, there is no sensation of filling and incontinence occurs. And compared to above, there is no reflex micturition in this case.
EDIT: I'm not really sure. I hope someone corrects me if I am wrong.
