sheaths

A sheath is a protective covering that encases or encloses another object. The term is used across disciplines to describe coverings in anatomy, botany, engineering, and everyday objects. Common senses include nerve and tendon sheaths, leaf sheaths in plants, protective jackets for cables, and sheaths for blades and tools.

In anatomy, a nerve sheath refers to layers that surround nerve fibers. The myelin sheath, produced by glial cells (Schwann cells in the peripheral nervous system and oligodendrocytes in the central nervous system), insulates axons and speeds electrical conduction. Tendon sheaths are synovial membranes that envelop certain tendons, reducing friction during movement; inflammation of a tendon sheath is called tenosynovitis.

In botany, a leaf sheath is the portion of a grass leaf that wraps around the stem, often enclosing the next leaf or inflorescence. In some plants, the sheath is a leaf base modified to protect or support the stem.

In engineering and everyday use, a sheath can be the outer protective covering of cables or wires, providing mechanical protection and environmental resistance. Materials vary and may include plastics, rubber, or composites; the jacket may also serve as electrical insulation and moisture barrier.

In weapons and tools, a sheath (or scabbard) is a case used to hold a blade when not in use. They are commonly made of leather, wood, metal, or synthetic materials and designed for safe storage and rapid access.

Other uses include plant structures that enclose seeds or buds, as well as protective coverings used in textiles and architecture where the term “sheath” conveys a surrounding envelope.