The aims of this chapter are to explain and present the older and new concepts and understanding around the microanatomy of nerve roots, trunks, and peripheral nerves. More recent work over the past 3 or 4 years looked at nerves with high-definition ultrasound and electron microscopy and illustrated that the paraneural or circumneural sheath is what neurosurgeons for years have been calling the “gliding apparatus” of the nerve. The space just deep to this layer is the subcircumneural (subparaneural) space, which should most probably be the target space for successful and safe single-injection block and catheter placement for continuous nerve block. The different microanatomical features of spinal roots, plexus trunks, and peripheral nerves are discussed and compared, as well as the microanatomical explanation of the different sonographical appearance of these three types of nerves.
Keywords: Anterior motor spinal root, Anterior scalene muscle, Arachnoid mater, Arachnoid villi, Arachnoid villus, Circumneural sheath, Circumneurium, Cross-over of muscle fibers, Dorsal middle scalene muscle, Dorsal scapular nerve, Dura mater, Epimysium, Epineurium, Long thoracic nerve, Paraneural cyst, Paraneural sheath, Phrenic nerve, Pia mater, Posterior scalene muscle, Posterior sensory spinal root, Prevertebral layer of deep cervical fascia, Scalene minimi muscle, Subcircumneural space, Subepimyseal space, Subparaneural space, Ventral middle scalene muscle.