1 There are two types of glial cells in the nervous system: the large-bodied macroglia and the smaller microglia. 2  There are two classes of macroglia in the central nervous system: astrocytes and oligodendrocytes.
Exports directly contribute and imports directly reduce their nation's balance of trade (i.e. net exports). A trade surplus is positive net balance of trade, and a trade deficit is a negative net balance of trade.
The U.S. had a trade surplus with NAFTA countries of $28.3 billion for services in 2009 and a trade deficit of $94.6 billion (36.4% annual increase) for goods in 2010. This trade deficit accounted for 26.8 percent of all U.S. goods trade deficit.