We not only have to know where the nerves live to be successful with RA & APM, it is also critically important to know what it lives in. In other words what membranes and barriers surround the nerves. Without this knowledge nerve blocks, especially continuous nerve blocks simply cannot be successful. Secondary nerve block failure after CPNB is a direct effect of not understanding the microanatomy of the nerves. This section explains the microanatomy that is at an absolute minimum essential for the practice of RA and APM.