The Nodes of Ranvier were discovered by the French physician, pathologist, histologist, and anatomist Louis-Antoine Ranvier when he observed the most fundamental parts of our nervous system, neurons. Noting the gaps between the myelin sheaths along neuron axons, he set out to discover their functions in aiding neural transmission.
The primary function of the Nodes of Ranvier is to speed up the transmission of neural impulses in nerves. Within this primary function, the sub-functions of the Nodes of Ranvier include the maintenance and correction of the impulse action potential which maintains efficient saltatory conduction.
Not only do the Nodes of Ranvier correct and repair the waves transmitted through the neural fibers, they potentially build up the standard action potential of the wave's trough and its subsequent standard electrical current. The hugely-present pressure-gated sodium channels found within the Nodes of Ranvier can contribute to increasing the electrical current's speed.
The Primary Function Of Nodes Of Ranvier
The first function of the Nodes of Ranvier is to speed up the transmission of neural impulses along the axon of some nerves. The axon is the nerve fiber between the nerve cell and dendrites and the axon terminals.
The myelin sheath covers the axon, which comprises concentric layers of lipids, including cholesterol, variable amounts of phospholipids, and cerebrosides, separated by thin protein layers. The sheath protects to axon from positively charged atoms and molecules external to the axon. The myelin sheath offers high-resistance and low-capacitance electrical insulation.
The myelin sheath is like the coating on an electrical wire, except that it has equidistant gaps along the axon. These gaps measure 1µm and are sometimes referred to as myelin gaps, but they are better known as the Nodes of Ranvier. The sodium ions present at the Nodes of Ranvier are kept in place by the Schwann cells so that depolarization will only occur at the Nodes of Ranvier.
How Do The Nodes Of Ranvier Speed Up Electrical Impulses?
The Nodes of Ranvier act as miniature trampolines of charge along the axon, causing the electrical impulse to depolarize momentarily and "hop" from node to node, reaching a transmission speed of up to 120 meters per second, which is about ten times faster than non-myelinated nerve fibers.
The manner of hopping as a means of propagating action potentials along the myelinated axon to increase their conduction velocity is called saltatory conduction.
Saltatory conduction also conserves the energy for the axon as depolarization occurs only at the Nodes of Ranvier. As a result, the ions move 100 times less than those in unmyelinated nerve fibers. The energy conserved in this process allows for re-establishing ion differences (including sodium, chloride, and potassium) across the membranes.
This video explains how the Nodes of Ranvier speed up electrical impulses along the axon.
Why Should Electrical Impulses Be Transmitted Speedily?
The inside of an axon is negatively charged, while the outside of the axon is positively charged. Without the myelin sheath, there would be constant depolarization of the impulse because of the exchange of ions between the inside and outside of the axon. This depolarization would cause an impulse to slow down as a result.
It is important to have increased transmission speed for faster reaction time. When you experience a potentially dangerous sensation, the message is sent via the nervous system to the brain, which decides how to respond physically. In other words, the faster your nerves work to convey the message of danger, the faster you can remove yourself from the danger.
Consider this scenario: You reach your hand into an oven to pick up a dish. Your finger touches the grill element, and you quickly snatch your hand back without picking up the dish. You have a little burn mark on your finger, but it could have been worse if you had left it there any longer.
Sub-Function Of Nodes Of Ranvier: Maintenance of Ions
The Nodes of Ranvier have increased voltage-gated sodium channels, allowing for the exchange of certain ions. Sodium and chloride are examples of such ions. These ions are required to form an action potential, which is the reversal of electrical polarization of neural membrane that can either initiate or be a part of the hop (or a wave excitation) that travels along the axon.
At each node, the action potential is propagated by the Node of Ranvier, which is regenerated, allowing it to jump to the next Node of Ranvier, where it is regenerated again. The constant energizing of the action potential allows it to travel rapidly along the axon by saltatory conduction.
The benefit of saltatory conduction is that much less energy is consumed due to less depolarization. As a result, the Schwann membrane and the Nodes of Ranvier can regenerate by re-establishing their ion balances of sodium, chloride, and potassium across the membranes.
The myelin sheath is protected by a thin layer of cells called Schwann cells, a membrane that protects the neuron from external electrical impulses. The channels at the Nodes of Ranvier are the only places along the axon where depolarization can occur. The Schwann cells block the movement of the ions along the axon, keeping them at the nodes.
When there is a myelin sheath degeneration (called demyelination), action potentials circulate as current loops between the Nodes of Ranvier instead of hopping along the axon by saltatory conduction. The transmission of action potentials is slowed, and there is a decrease in reaction time.
Sub-Function Of Nodes Of Ranvier: Controlling Impulse Parameters
Impulses that arrive at the nerve cell are repaired and regulated as they move along from node to node. The Nodes of Ranvier aid in regulating these impulses, but some variables can affect the speed of the saltatory conduction. The following are some of the variations in Nodes of Ranvier that can influence the parameters of the speed of the impulses:
- The internode length between the Nodes of Ranvier on an axon,
- The difference in the size of the Nodes of Ranvier,
- The amount of liquid released at the Node of Ranvier,
- The type of nerve (e.g., optic, cortex, etc.),
- The number of myelin wraps,
- Conductance of Sodium and Potassium ions, and
- Conductance of myelin sheath.
In Which Nerves Will You Find Nodes Of Ranvier Functioning?
Not all nerves contain Nodes of Ranvier as not all nerves are myelinated. Nerves containing myelin sheaths can be found in the central nervous system. This includes the nerves in the brain, the spinal cord, and other sensory nerves like the optic nerves.
As we have read, myelinated nerve fibers have Nodes of Ranvier to speed up the conduction of impulses by using Saltatory Conduction. On a survival level, increased conduction of impulses is required when we sense danger to react accordingly to minimize our chances of getting hurt.
Nerve fibers can be categorized into three groups:
- Group A nerve fibers, which are heavily myelinated,
- Group B nerve fibers, which are moderately myelinated, and
- Group C nerve fibers are unmyelinated.
Group C nerve fibers will not contain Nodes of Ranvier due to the lack of a myelin sheath surrounding the axon.
Group A Nerve Fibers
Group A nerve fibers are heavily myelinated and offer speedier conduction of electrical impulses for speedier reaction time. They can be found in motor and sensory pathways. If danger is sensed, a quick motor reaction is usually required.
A-alpha nerve fibers deliver information regarding proprioception or muscle sense. A-beta nerve fibers deliver information regarding touch. A-delta nerve fibers convey information regarding pain and temperature.
Group B Nerve Fibers
Group B nerve fibers are small axon fibers and are only moderately myelinated. They do not conduct impulses at such a high velocity. Group B nerve fibers can be found in visceral nerves, including the vagus nerve.
The table below compares the speed of conductivity between Group A and Group B nerve fibers.
|Fiber Type||Subtype||Conductance velocity (m/s)|
How To Maintain Optimal Functioning Of The Nodes Of Ranvier
To maintain optimal functioning of Nodes of Ranvier so that your reaction time is the best, you need to maintain healthy myelination and understand the electrical principles of healthy Node of Ranvier function. But how do you do that?
Selfhacked recommends the following ways to look after the myelin and, therefore, healthy Nodes of Ranvier in your body:
- Make good lifestyle choices
- Include the right foods into your diet
- Check your hormone levels
Make Good Lifestyle Choices
Lifestyle choices that may promote myelin health include getting enough sleep, regular exercise, socializing, exposure to new situations, and learning new and complex skills.
Sleep has long been associated with body regeneration, including the higher expression of the gene coding for myelination. Sleep also intensifies the amount of oligodendrocyte precursor cells (OPCs) within the body, which can assist in increased myelin formation.
Research has indicated that exercise appears to increase mitochondrial function, which may increase myelin production. Exercise is also useful in myelin repair after an injury or in individuals with Alzheimer's.
Socialization And Exposure To New Experiences
Limited research has indicated a correlation between the effect of socialization and exposure to new experiences on the development of myelin. It is especially apparent in the brains of infants exposed to enriched environments, where the frontal lobe and internal capsule of their brains saw the increased structure of white matter, i.e., myelin growth.
The opposite is also true for severely neglected children, with a 17% reduction in the corpus callosum area. The Saltatory conduction rate in severely neglected children would be much slower due to the lack of myelin and impaired Nodes of Ranvier. This means their reaction time would be delayed, leading to further developmental delays.
Learning A Complex Skill
When you learn new and complex skills, you build neural pathways and increase the white matter that constitutes the fatty myelin sheath. Learning to play a musical instrument is an example of a complex skill, and the growth of white matter is proportionate to the number of hours spent learning the skill.
When you make good lifestyle choices such as the ones listed above, you will improve the functioning of your Nodes of Ranvier, thereby maintaining and increasing the saltatory conduction in your Group A and Group B nerve fibers.
Include The Right Foods In Your Diet
You can include certain foods, vitamins, and minerals in your diet that will encourage the growth of myelin and the development of the Nodes of Ranvier in your nerve fibers. Some foods, vitamins, and minerals that will benefit this cause include:
- Biotin activates enzymes that are necessary in energy production and myelin synthesis.
- Cholesterol is essential for myelin but should not be taken in excess.
- Choline enhances myelin repair.
- Fish (DHA) help the nerve fibers in your brain.
- Folate (Vitamin B9) for your brain nerve fibers.
- Iron is important for cell function; a lack of iron causes demyelination.
- Lecithin is an integral part of myelin.
- Pantothenic Acid (Vitamin B5) supports fatty acid synthesis.
- Phosphatidylserine is needed for healthy nerve cell membranes and myelin.
- Thiamine (Vitamin B1). A lack of thiamine is linked to neurological diseases like Parkinson's, Huntington's, and Alzheimer's.
- Vitamin B12 assists with myelin sheath formation.
- Vitamin C helps with many enzyme reactions, including those needed for myelination.
- Vitamin D3 for functional nerve recovery.
- Vitamin K is needed for increased sulfatide production needed in myelination.
- Zinc is needed for myelin proteins to function effectively.
Check Your Hormone Levels
Melatonin, Progesterone, Insulin-like growth factor-1 (IGF-1, Testosterone, and Prolactin are some of the hormones associated with the successful functioning of myelin sheaths and the Nodes of Ranvier. Before using supplements, you should talk to your doctor or health professional.
When Do The Nodes Of Ranvier Not Function as They Should?
When the Nodes of Ranvier are not working optimally, it will affect Saltatory Conduction, which can cause a disturbance in the Central or Peripheral Nervous Systems. This disturbance may result in delayed reaction times, which could either affect one's ability to react to a dangerous situation or it could slow down response and movement in general.
What Can Cause Demyelination?
Demyelination and the subsequent breakdown of the Nodes of Ranvier can be caused by issues arising during development, injury, lack of self-care, or diseases that affect nerve fibers or the node-associated proteins that link to cognitive disorders.
Inflammation causes demyelination and oligodendrocyte (OL) destruction due to cytokines, including TNF alpha and lymphotoxin (LT).
Multiple Sclerosis is a disease that causes the demyelination of Central Nervous System axons. These axons affect many parts of the brain and spinal cord and lead to loss of vision, paresthesia, paralysis, numbness, and other issues. Cytokines are more prolific at lesion sites and in the Cerebrospinal fluid of these patients.
Strangely enough, a simple sugar called N-acetylglucosamine, a simple sugar in breast milk, is considered a dietary supplement that promotes myelination in patients with Multiple Sclerosis in the United States.
Early onset of binge drinking of alcohol increases demyelination, decreasing white matter in the corpus callosum, and will have a longer-term effect on the functioning of the nerve fibers.
Statins, which are used to control heart disease and maintain cholesterol levels, are also linked to demyelination. Cholesterol forms an integral part of the myelin sheath, which is needed for the Nodes of Ranvier to be present and fully functional.
Some psychiatric disorders are associated with subtle dysfunction of the Nodes of Ranvier. These disorders include schizophrenia, personality disorder, bipolar disorder, and autism. The abnormalities observed noted abnormalities in white matter in the brain. Patients with bipolar disorder and schizophrenia have identified changes in the proteins of the Nodes of Ranvier.
Although the Nodes of Ranvier have not been directly implicated in this research, there seems to be a correlation with ankyrin G in node development in patients with autism, Attention Deficit/Hyperactivity Disorder (ADHD), epilepsy, and intellectual disability. The correlation between ankyrin G in node development in these patients needs to be explored further.
Mutations that occur in the CNTN2 and CNTNAP2 genes of the juxtaparanodes of the Nodes of Ranvier correlate with patients on the autistic spectrum, epilepsy, Tourette's Syndrome, schizophrenia, and ADHD. It is still unclear how these mutations affect these disorders, but their presence indicates a link nevertheless.
The primary function of the Nodes of Ranvier on nerve fibers is to speed up the velocity of neural impulses in the central and peripheral nervous systems through a process called Saltatory Conduction. The impulse can be conveyed at a speed of up to 120 meters per second, depending on the type of nerve fiber and its function.