The yellow arrow indicates which structure in the cross-section of a myelinated nerve fiber?

The yellow arrow indicates which structure in the cross-section of a myelinated nerve fiber?

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

Answer: (D)

In a cross-section of a myelinated nerve fiber, you can see the myelin sheath as multiple concentric lamellae around the axon. Within this sheath are tiny cytoplasmic channels called Schmidt-Lanterman clefts. They appear as small, irregular pockets or gaps within the myelin where Schwann cell cytoplasm remains, allowing metabolic exchange and maintenance of the sheath. They are distinctive to peripheral nerve myelin and help explain why there are occasional spaces inside the otherwise tightly wrapped layers. Nodes of Ranvier would show up as gaps along the length of the axon, not as features within the myelin sheath in cross-section. The epineurium is the outer covering of the entire nerve, not something seen within individual myelin lamellae. A myelinated axon would show the axon core with surrounding myelin, but without the characteristic intramyelin clefts.

In a cross-section of a myelinated nerve fiber, you can see the myelin sheath as multiple concentric lamellae around the axon. Within this sheath are tiny cytoplasmic channels called Schmidt-Lanterman clefts. They appear as small, irregular pockets or gaps within the myelin where Schwann cell cytoplasm remains, allowing metabolic exchange and maintenance of the sheath. They are distinctive to peripheral nerve myelin and help explain why there are occasional spaces inside the otherwise tightly wrapped layers.

Nodes of Ranvier would show up as gaps along the length of the axon, not as features within the myelin sheath in cross-section. The epineurium is the outer covering of the entire nerve, not something seen within individual myelin lamellae. A myelinated axon would show the axon core with surrounding myelin, but without the characteristic intramyelin clefts.