Which connective tissue surrounds each fascicle within the peripheral nerve?

Which connective tissue surrounds each fascicle within the peripheral nerve?

• A. Epineurium
• B. Nodes of Ranvier
• C. Perineurium
• D. Clefts of Schmidt-Lanterman

Answer: (C)

The key idea is that the fascicle—the bundle of nerve fibers inside a peripheral nerve—is wrapped by a specialized connective tissue sleeve called the perineurium. This perineurial sheath consists of concentric layers of cells with tight junctions that create a diffusion barrier, helping to maintain a stable internal environment for the fibers and providing mechanical protection as the nerve moves. It’s the specific layer that sits around each individual fascicle, distinguishing it from other coverings. By contrast, the outermost layer, the epineurium, surrounds the entire nerve, holding many fascicles together. The innermost layer around each individual axon within a fascicle is the endoneurium, which is looser connective tissue with capillaries and supportive cells. The other terms refer to structures not serving as the wrapping around a fascicle: nodes of Ranvier are gaps along myelinated segments essential for saltatory conduction, and Schmidt-Lanterman clefts are cytoplasmic channels within the myelin sheath of Schwann cells.

The key idea is that the fascicle—the bundle of nerve fibers inside a peripheral nerve—is wrapped by a specialized connective tissue sleeve called the perineurium. This perineurial sheath consists of concentric layers of cells with tight junctions that create a diffusion barrier, helping to maintain a stable internal environment for the fibers and providing mechanical protection as the nerve moves. It’s the specific layer that sits around each individual fascicle, distinguishing it from other coverings.

By contrast, the outermost layer, the epineurium, surrounds the entire nerve, holding many fascicles together. The innermost layer around each individual axon within a fascicle is the endoneurium, which is looser connective tissue with capillaries and supportive cells. The other terms refer to structures not serving as the wrapping around a fascicle: nodes of Ranvier are gaps along myelinated segments essential for saltatory conduction, and Schmidt-Lanterman clefts are cytoplasmic channels within the myelin sheath of Schwann cells.