Please note that the spinal roots for L2 through S5 all descend in the cauda equina and injury to these roots would disrupt sensory and motor fibers from these segments. Strictly speaking, the spinal roots are part of the peripheral nervous system as opposed to the spinal cord. Peripheral nerves are supposed to be able to regenerate to some extent.
A unit of measurement is a definite magnitude of a quantity, defined and adopted by convention or by law, that is used as a standard for measurement of the same quantity. Any other value of that quantity can be expressed as a simple multiple of the unit of measurement. For example, length is a physical quantity. The metre is a unit of length that represents a definite predetermined length. When we say 10 metres (or 10 m), we actually mean 10 times the definite predetermined length called metre.
Common Metric Measures. The metric system is also divided into different categories of measurement, but it has a base unit for each category. A base unit means that that is what the category is usually (but not always) measured in, and all the other terms of measurement in that category are built from the base unit.