Which structure does the yellow arrow mark in the diagram?

Which structure does the yellow arrow mark in the diagram?

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

Answer: (A)

This is about identifying the outermost protective tissue layer of a peripheral nerve. The yellow arrow points to the epineurium, a dense irregular connective tissue sheath that surrounds the entire nerve and includes the blood vessels (vasa nervorum) that supply it. This outer layer protects and supports the nerve as a whole. Inside this outer layer lie the fascicles, each wrapped by the perineurium, which forms the blood-nerve barrier, and inside those fascicles are individual axons wrapped by the endoneurium. The other structures shown in nerves—nodes of Ranvier are gaps between myelin segments along an axon, and Schmidt-Lanterman clefts are cytoplasmic channels within the myelin—are features inside the nerve, not the outermost covering.

This is about identifying the outermost protective tissue layer of a peripheral nerve. The yellow arrow points to the epineurium, a dense irregular connective tissue sheath that surrounds the entire nerve and includes the blood vessels (vasa nervorum) that supply it. This outer layer protects and supports the nerve as a whole. Inside this outer layer lie the fascicles, each wrapped by the perineurium, which forms the blood-nerve barrier, and inside those fascicles are individual axons wrapped by the endoneurium. The other structures shown in nerves—nodes of Ranvier are gaps between myelin segments along an axon, and Schmidt-Lanterman clefts are cytoplasmic channels within the myelin—are features inside the nerve, not the outermost covering.