Femke Mathot

Chapter 1 14 10 Considering its function, optimization of revascularization of repaired peripheral nerves hypothetically forms an opportunity to improve nerve regeneration outcomes. Figure 1. Cross sectional anatomy of a peripheral nerve. (Used with permission of the American Society of Regional Anesthesia and Pain Medicine. All rights reserved.) NERVE SUBDIVISIONS Besides sensory, motor and mixed nerves, the peripheral nervous system can be subdivided in multiple other ways. When studying the direction of the transmitted stimuli, one can distinguish either afferent (towards the central nervous system) and efferent (away from the central nervous system) nerve fibers. Motor fibers are classified as efferent, sensory fibers are mostly afferent. The somatic versus autonomic nervous system are distinguished based on their control mechanism. The somatic system comprises voluntary actions that we can control like the movement of skeletal muscles. Actions of internal organs like cardiac contraction and digestive movements of the colon are involuntary and belong to the autonomic nervous system. 11 On a axonal level, axon fibers can be subdivided into either myelinated and unmyelinated axons. Myelin, which consist for approximately 80% of lipids, is formed by Schwann cells in the peripheral nervous system. Each Schwann cell wraps around one segment of an axon many times to form a myelin sheet: an internode. 12 The amount of myelin that is formed by the Schwann cells is related to the diameter and the function of the axon and neuron. 13 The gaps between each of the internodes are called nodes of Ranvier and contain many sodium and