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.
Noun. 1. balance of trade-the difference in value over a period of time of a country's imports and exports of merchandise; a nation's balance of trade is favorable when its exports exceed its imports. trade balance, trade gap, visible balance.