A good practical knowledge of anatomy is important for the successful and safe practice of regional anesthesia. In fact, just as surgical disciplines rely on surgical anatomy, regional anesthesiologists need to have a working knowledge of the anatomy of nerves and associated structures that does not include unnecessary details. In this chapter, the basics of regional anesthesia anatomy necessary for successful implementation of various techniques described later in the book are outlined.
All peripheral nerves are similar in structure. The neuron is the basic functional unit responsible for the conduction of nerve impulses (Figure 1-1). Neurons are the longest cells in the body, many reaching a meter in length. Most neurons are incapable of dividing under normal circumstances, and they have a very limited ability to repair themselves after injury. A typical neuron consists of a cell body (soma) that contains a large nucleus. The cell body is attached to several branching processes, called dendrites, and a single axon. Dendrites receive incoming messages; axons conduct outgoing messages. Axons vary in length, and there is only one per neuron. In peripheral nerves, axons are very long and slender. They are also called nerve fibers.
Organization of the peripheral nerve.
The individual nerve fibers that make up a nerve, like individual wires in an electric cable, are bundled together by connective tissue. The connective tissue of a peripheral nerve is an important part of the nerve. According to its position in the nerve architecture, the connective tissue is called the epineurium, perineurium, or endoneurium (Figure 1-2). The epineurium surrounds the entire nerve and holds it loosely to the connective tissue through which it runs. Each group of axons that bundles together within a nerve forms a fascicle, which is surrounded by perineurium. It is at this level that the nerve–blood barrier is located and constitutes the last protective barrier of the nerve tissue. The endoneurium is the fine connective tissue within a fascicle that surrounds every individual nerve fiber or axon.
Histology of the peripheral nerve and connective tissues. White arrows: External epineurium (epineural sheath), 1 = Internal epineurium, 2 = fascicles, Blue arrows: Perineurium, Red arrow: Nerve vasculature Green arrow: Fascicular bundle.
Nerves receive blood from the adjacent blood vessels running along their course. These feeding branches to larger nerves are macroscopic and irregularly arranged, forming anastomoses to become longitudinally running vessel(s) that supply the nerve and give off subsidiary branches.
The nervous system consists of central and peripheral parts. The central nervous system includes the brain and spinal cord. The peripheral nervous system consists of the spinal, cranial, and autonomic nerves, and their associated ganglia. Nerves are bundles of nerve fibers ...