In the economy, there is a circular flow of income and spending. 1  Everything is connected. Money that is earned flows from one person to another, and most of it gets spent again - not just once, but many times.
Stage 1: excitement or arousal. A man gets an erection with physical or psychological stimulation, or both. This causes more blood to flow into three spongy areas (called corpora) that run along the length of his penis. The skin is loose and mobile, allowing his penis to grow.
Another area of the hypothalamus is responsible for shutting down the brainâs arousal signals and causing the transition to sleep. Neurons in a part of the hypothalamus called the ventrolateral preoptic nucleus (VLPO) connect directly to the many arousal-promoting centers.