Neurons make up the brain, spinal cord and nerves that connect to our bodies, and they control all function in our bodies. They are coated in a thick insulation that has small breaks, called nodes of Ranvier. This lesson explains the structure and function of the nodes of Ranvier.
What are the Nodes of Ranvier?
Before we can get a clear definition of the nodes of Ranvier, we should first get a better understanding of what neurons are and how they work. Neurons have three key parts: the dendrites, which receive signals, the cell body, which contains the nucleus, and the axon, which sends signals. The axon is coated in a fatty substance called myelin, which is secreted by cells called oligodendricytes or Schwann cells. Below is a diagram of the parts of a neuron.
Myelin insulates the neuron like plastic insulates electrical wires. Neurons send signals using electricity, so the myelin helps to keep the signal moving quickly over long distances. Think of the coating on wires in your house that prevents the electric current from diffusing out of the wires, and helps to move the current faster. Myelin does the same thing. But, in order for the signal to propagate through the neuron, there must be breaks in the myelin coating.
These breaks are called nodes of Ranvier. Below is a diagram of a support cell, the oligodendricyte, wrapped around the axon, creating the myelin sheath and nodes of Ranvier.
Nodes of Ranvier are the spaces between the myelin coating on the neuron's axon. Much like the plastic coating on a wire needs to be clear to connect to an appliance and supply power, there must be breaks in the myelin to conduct electricity in neurons.
Electricity travels quickly through the axon wrapped in myelin. At the nodes of Ranvier, electricity can be conducted within the cell's environment, and the electrical signal will be propagated down the axon.
Nodes of Ranvier have space exposed to conduct electricity with the environment to propagate the signal down the axon. At the nodes of Ranvier the cell membrane, or boundary of the cell is exposed. This part of the membrane has proteins, called channel proteins, which allow ions to enter and exit the cell. They're like doors for the cell, letting specific people in and out.
This whole process is largely controlled by sodium and potassium ions. Below is a diagram of the sodium and potassium ion channels in neurons. These channels are in the membrane at the nodes of Ranvier.
Since the nodes of Ranvier are spread out, the electrical impulse jumps down the axon between the nodes, called saltatory conduction. Ions move in and out at the first node of Ranvier, causing an electrical impulse in the neuron. The signal then jumps to the next node, allowing the signal to move quickly and efficiently down the neuron. In the image below, the electrical impulse is shown moving down one axon to send a signal to the next neuron.
Nodes of Ranvier are gaps in the myelin sheath coating on the neural axon. The myelin allows the electrical impulse to move quickly down the axon. The nodes of Ranvier allow for ions to diffuse in and out of the neuron, propagating the electrical signal down the axon. Since the nodes are spaced out, they allow for saltatory conduction, where the signal rapidly jumps from node to node. The result is efficient electrical communication throughout the body's nervous system.
Medical Disclaimer: The information on this site is for your information only and is not a substitute for professional medical advice.
Dendrites - parts of a neuron that receive signals
Cell body - portion of a neuron that contains the nucleus
Axon - part of a neuron that sends signals
Myelin - a fatty substance that coats the axon
Schwann cells - also known as oligodendricytes; cells that secrete myelin
Nodes of Ranvier - breaks in the myelin coating that allow signals to propagate through a neuron
Saltatory conduction - the jumping of electrical impulses down the axon between the spread-out nodes of Ranvier
After viewing this lesson, check to see if you can:
- Identify the parts of a neuron
- Describe the function of the nodes of Ranvier