Most neurons are insulated by a myelin sheath formed by cells (Schwann cells) surrounding the axons. Bundles of fibres from neurons held together by connective tissue form nerves.

• 大多数的神经元由一层包绕周围轴突的髓鞘(其细胞现称施万氏细胞)与外界隔绝。成束的来自多数神经元的纤维由结缔组织包绕形成神经。