Nodes of Ranvier or myelin-sheath gaps are a type of specialized cell along the axons that contain sodium and potassium ion channels, allowing the action potential to travel quickly down the axon by jumping from one node to the next.
A node of Ranvier is a natural gap in the myelin sheath along the axon. These spaces are about one micrometer long and contain voltage-gated Na+ and K+ channels. The flow of ions through these channels, particularly the Na+ channels, regenerates the action potential over and over again along the axon. Action potential “jumps” from one node to the next in saltatory conduction. If nodes of Ranvier were not present along an axon, the action potential would propagate very slowly; Na+ and K+ channels would have to continuously regenerate action potentials at every point along the axon. Nodes of Ranvier also save energy for the neuron since the channels only need to be present at the nodes and not along the entire axon.
Nodes of Ranvier: Nodes of Ranvier are gaps in myelin coverage along axons. Nodes contain voltage-gated K+ and Na+ channels. Action potentials travel down the axon by jumping from one node to the next.
Key Points
• Nodes of Ranvier are gaps in the myelin along the axons; they contain sodium and potassium ion channels, allowing the action potential to travel quickly down the axon by jumping from one node to the next.
• Nodes of Ranvier also save energy for the neuron since the channels only need to be present at the nodes and not along the entire axon.
Key Terms
node of Ranvier: a small constriction in the myelin sheath of axons
action potential: a short term change in the electrical potential that travels along a cell
myelin sheath: acts to protect the nerves from other electrical impulses, and speeding the time it takes for a nerve to traverse an axon
Na+ and K+ channels: protein channels that allow the movement of sodium and potassium ions in the nerve cell
saltatory conduction: is the propagation of action potentials along myelinated axons from one node of Ranvier to the next node
