Figure 4-12 Four possible target sites for inhaled anesthetic molecules (solid circles) in a neuronal membrane include the lipid bilayer as a whole (a), lipids at a protein-lipid interface (b), a protein site bounded by lipid (c), and a protein site exposed to an aqueous environment (d). (Adapted from Franks NP, Lieb WR: What is the molecular nature of general anesthetic target sites? Trends Pharmacol Sci 8:169, 1987.)