9781422279656

Words to Understand in This Chapter

narcotic— a drug that in small doses dulls the senses, relieves pain, and induces sleep, but in larger doses can depress breathing and heartbeat. neurotransmitters— chemicals that are released at the end of a nerve and carry messages to other parts of the body. synaptic cleft— a microscopic gap between neurons. The nervous system uses neurotransmitters to send messages across this gap. synthetic— a substance that is created in a laboratory by blending chemicals. Synthetic substances often imitate a natural product. withdrawal— a syndrome of physical and emotional symptoms that a person addicted to heroin or opioids experiences when the person stops using the drug.