Q CLINICAL CASE REPORT Chapter 11 Running Problem: A Powerful Addiction 1. What is the usual response of cells that are chronically exposed to elevated concentrations of a signal molecule? 2. What happens to a postsynaptic cell when nicotine rather than ACh binds to a nicotinic cholinergic receptor? 3. Although ACh and nicotine have been shown in short-term studies to be nAChR agonists, continued exposure of the receptors to ACh has been shown to close, or inactivate, the channel. Speculate why this could explain the up-regulation of nAChR observed in smokers. 4. Name another ion channel you have studied that opens in response to a stimulus but inactivates and closes thereafter.