What structure is indicated by the black arrow?

What structure is indicated by the black arrow?

• A. Clefts of Schmidt-Lanterman
• B. Node of Ranvier
• C. Perineurium
• D. Peripheral nerve

Answer: (B)

In myelinated nerves, electrical signals travel fastest when they can jump from one bare region of the axon to the next. That bare region between myelin segments is the Node of Ranvier. These nodes are where the axon is exposed and packed with voltage-gated sodium channels, which recharge the signal as it passes along. The arrow is pointing to that gap, not to the myelin-covered parts. Clefts of Schmidt-Lanterman are small cytoplasmic channels inside the myelin sheath, not gaps between myelin segments. The perineurium is the protective sheath around a bundle of nerve fibers, and a peripheral nerve refers to the whole bundle, not a single node. So the node of Ranvier is the structure indicated.

In myelinated nerves, electrical signals travel fastest when they can jump from one bare region of the axon to the next. That bare region between myelin segments is the Node of Ranvier. These nodes are where the axon is exposed and packed with voltage-gated sodium channels, which recharge the signal as it passes along. The arrow is pointing to that gap, not to the myelin-covered parts.

Clefts of Schmidt-Lanterman are small cytoplasmic channels inside the myelin sheath, not gaps between myelin segments. The perineurium is the protective sheath around a bundle of nerve fibers, and a peripheral nerve refers to the whole bundle, not a single node. So the node of Ranvier is the structure indicated.