Peripheral nerves arise from the spinal cord, and they contain axons from different types of neurons serving various effector organs or sensory endings. The cell bodies of motor neurons that innervate skeletal muscle fbres are situated in the anterior horns of the grey matter of the spinal cord. Enlargements of the cord in the cervical and lumbar segments mark the major regions supplying the upper and lower limbs (Fig. 1.1). The frst sensory neurons are situated in the dorsal root ganglia, which are located in the intervertebral foramina, just proximal to the fusion of the anterior and posterior roots. The peripheral nerve is composed of motor, sensory and sympathetic nerve fbres. A nerve fbre is the conducting unit of the nerve and contains the following elements: a central core, the axon and Schwann cells. Some nerve fbres are surrounded by a myelin component (myelinated nerve fbres), and others are free of such myelin sheath (unmyelinated nerve fbres) .