The chemical substances involved are called neurotransmitters. Specific sites on the adjacent site bind with the neurotransmitter and this interaction triggers a response in the neuron. Among the things involved are perception of pain, emotion, interpretation of audio and visual stimuli. This context generally is lacking in our present day culture in this country. Many synthetic ones are also known, e.g., LSD and heroin.
Cannabis is probably native to central Asia.
The plant was early used from the Near East to China. This plant is the source of fiber. Seed oils from cannabis are used in many Asian cultures. The plant has also been used medicinally and for its psychoactive properties. Diagram of plant page 416.