Tiam Mana Saffari

12 CHAPTER 1 BACKGROUND Peripheral nerve injuries occur in approximately 5% of all trauma cases. The majority of these cases rarely recover completely and can cause lifelong physiological and functional disabilities leading to a diminished quality of life 1-3 . The most common nerve injuries are caused by high energy traumas, such as motor vehicle accidents. In addition, penetrating wounds and lacerations caused by tumor excision result in injuries to the peripheral nervous system 4,5 . The peripheral nervous system is one of two components that make up the nervous system, with the other subdivision being the central nervous system. The central nervous system, comprising the brain and spinal cord, integrates data and conducts impulses via a network of peripheral nerves consisting of bundles of nerve fibers or axons 6 . ANATOMY OF THE PERIPHERAL NERVOUS SYSTEM The peripheral nervous system consists of the somatic and autonomic division. The somatic division is associated with voluntary movement and sensibility, controlled by motor and sensory neurons, respectively. The autonomic division mediates visceral functions, such as heart rate and digestion 7 . This thesis will solely focus on the somatic subdivision of the peripheral nervous system. Each peripheral nerve trunk consists of many axons, supported by an outer surrounding layer of fibrous connective tissue called the epineurium, and longitudinal blood vessels that supply the nerve with nutrients (Figure 1). Within the nerve, axons are bundled into fascicles (depicted with the square), each surrounded by their own perineurium. The epineurium and perineurium consist of layers of fibroblasts and collagen to provide tensile strength. Finally, the endoneurium surrounds each individual axon within the fascicles 8 . Myelinating Schwann cells insulate the axon with a myelin sheath, consisting of many regular layers of plasma membrane, that aids in conduction of nerve impulses. The nodes of Ranvier facilitate saltatory conduction by allowing action potentials to jump from node to node, resulting in increased velocity of conduction 9 . The blood supply source to peripheral nerves is called the vasa nervorum, consisting of small vessels that are adjacent to the nerve and torturous to allow for freedom of translational movement of peripheral nerves, particularly in the vicinity of joints. The vascular tree and the nervous branching networks are often patterned similarly in