The special relationship between central banks and financial markets also stems from the fact that the operational conduct of monetary policy involves buying and selling assets in financial markets, albeit not motivated narrowly by profit as a market participant is. From the markets' point of view, the central bank is a specialist participant whose assignment it is to make the money market.
The central bank's standing facilities to lend and accept deposits are nothing more than the bid-ask spread at which it is willing to deal in money. This very wide spread establishes the outermost bounds of the market. Most of the trading in the open market occurs at much narrower spreads.