The green arrow marks which feature in the nerve diagram?

The green arrow marks which feature in the nerve diagram?

• A. Nodes of Ranvier
• B. Myelinated axon
• C. Epineurium
• D. Perineurium

Answer: (A)

Recognizing gaps between myelin sheaths along a myelinated axon as Nodes of Ranvier is what's being tested. The green arrow points to a small interval where the myelin sheath is missing, exposing the axon. These gaps are where voltage-gated Na+ channels cluster and action potentials are regenerated, allowing the electrical signal to jump from node to node—saltatory conduction—which makes fast nerve impulse propagation possible. The surrounding white, insulating myelin segments are the myelinated portions of the axon, not the gaps. The other terms—epineurium and perineurium—are connective tissue coverings around nerve fibers or fascicles, not features along the axon itself.

Recognizing gaps between myelin sheaths along a myelinated axon as Nodes of Ranvier is what's being tested. The green arrow points to a small interval where the myelin sheath is missing, exposing the axon. These gaps are where voltage-gated Na+ channels cluster and action potentials are regenerated, allowing the electrical signal to jump from node to node—saltatory conduction—which makes fast nerve impulse propagation possible. The surrounding white, insulating myelin segments are the myelinated portions of the axon, not the gaps. The other terms—epineurium and perineurium—are connective tissue coverings around nerve fibers or fascicles, not features along the axon itself.