I don't have time for a big post, but a few pointers that may help:
The part of blue ring venom that is toxic to humans (there may be other components) is commonly called TTX (
tetrodotoxin.) It's the same toxin that is found in puffer fish and in a species of newt (? or is it salamander?), but in all these animals, it's actually produced by symbiotic bacteria. It's method of action is to bind to the voltage-gated sodium channels in nerve axons that are an important part of the system to send "action potentials" or "spikes" down the long part of the nerve (unlike wires, nerves actively propagate the signals). The TTX blocks these channels and essentially shuts down the animal's nervous system. In humans, the heart survives this, and the brain and spinal cord are protected by the blood-brain barrier, which TTX doesn't cross, but all of the peripheral nervous system can be shut down by TTX in the bloodstream (where the octo bit and injected it into the blood, or from the stomach for someone who ate Fugu or something.) In particular, that means that the nerves can't tell the muscles to breathe, so respiration stops. Fortunately, TTX only binds to these channels for around 12-24 hours, so if the person is put on a respirator, they can be kept alive for a while and recover. Unfortunately for that person, the brain is still working fine (because of the blood-brain barrier) so they're often conscious, aware, and alert, but can't breathe, talk, or move.
I'd suggest googling for TTX to find more information (including the full name). There are good articles on blue-rings on the cephalopod page, too, including this one:
http://www.thecephalopodpage.org/bluering1.php
another good google search might be "hapalochlaena"