Final answer:
Nicotine at low doses can promote relaxation and decrease inhibitions in the CNS. At high doses, it can cause sleep induction, motor disturbance, memory loss, decreased respiratory function, and death. These effects are due to nicotine's mimicry of acetylcholine.
Step-by-step explanation:
Nicotine, the active chemical in tobacco, has various effects on the central nervous system (CNS) at low doses. It can increase relaxation and decrease inhibitions. However, at high doses, nicotine can cause sleep induction, motor disturbance, memory loss, decreased respiratory function, and even death. These effects are due to nicotine's ability to mimic the neurotransmitter acetylcholine.