The role of stimulants in the nervous system is to enhance activity and alertness. These substances, such as caffeine and amphetamines, increase the release of neurotransmitters like dopamine and norepinephrine, resulting in heightened arousal, improved mood, and increased cognitive functions. While they can have beneficial effects in moderation, excessive stimulant use can lead to negative consequences, including addiction, anxiety, and cardiovascular issues. Understanding their effects is crucial for managing both therapeutic use and potential risks.