This is a common trick question. Even in the 21st century we don't understand how gas anesthetics work as their mechanism of action has not been identified. We do know how other anesthetics work. Local anesthetics act directly on the sodium channels of nerves and thus are injected directly adjacent to nerves. Most pain medications work on the opioid receptors. A notable exception is Ketamine which works with a wide variety of receptors. Propofol works on the GABA receptors.