Nerve Cell Damage from Schwannoma

Last Updated: 02/27/17

Index:

  1. Schwannoma and Nerve Damage
  2. Nerve Cell Function
  3. Definitions
    1. Neuron
    2. Nucleus
    3. Axon
    4. Glial
    5. Axon Terminal
    6. Dendrites
    7. Myelin
    8. Nodes of Ranvier
    9. Action Potential (AP)
  4. Sources

Also See:

While Neurofibromatosis Type 2 (NF2) results in eye issues as well as the potential growth of Meningioma and Ependymoma, the primary tumor growth type typical for the NF2 condition are Schwannoma. Schwannoma tumors are an overgrowth of Schwann Cells. Schwann Cells are a part of Nerve Cells for communication of senses and for impulse for movement of the body.

Depending on an individual's exact NF2 mutation type Schwannoma might grow on:

  • Cranial Nerve 8, the Vestibulocochlear Nerve which is responsible for the function of both the Cochlear Nerve (hearing) and Vestibular Nerve (balance nerve).
  • Cranial Nerve 7, the Facial Nerve (face movement).
  • Other Cranial Nerves, most commonly; Cranial Nerve 5 (Trigeminal Nerve), and CN 10 (Vagus Nerve)
  • Primarily Central Nerve System; nerves in brain and spinal cord
  • Peripheral Nerve System; nerves in the body including those which might be seen and felt under skin surface

1. Schwannoma and Nerve Damage

Overgrowth of Schwann Cell(s) inside of the nerve cells Myelin of a Nerve Cell, will result in fewer breaking points between Myelin for Node of Ranvier, each missing Node will mean less strength of Action Potential to carry sensory information along with a nerve. When a Schwann Cell overgrows and transitions to become a Schwannoma if it is threatening other nerves and is surgically removed or radiosurgery is used to stop the tumor, the nerve the Schwann grew on will no longer function.

If a Schwannoma grows slowly enough the mass can reach a considerable size before it results in complete loss of the nerve.

Neuron, Neurolema, Nerve Cell, Nucleus, Axon, Glial, Axon Terminal, 
	Dendrites, Myelin, Nodes of Ranvier, Action Potential, AP, Schwann Cell

2. Nerve Cell Function

The purpose of the Schwann cell on the Neuron is to control impulse signals along the Axons. Depending on what the purpose of the nerve would determine if the information was sensory or muscular in nature. To understand why and how Schwann Cell Damage can occur, it is best to understand the parts of a Nerve Cell and Action Potential.

3. Parts of the Nerve [Linus Pauling Institute, Glossary]

  1. Neuron: A Neuron (Nerve Cell), also called Neurone, or Neurolema, is an electrically excitable cell that processes and transmits information through electrical and chemical signals.

  2. Nucleus: A Neuron's Nucleus is the same as any Nucleus for any other cell type, containing the cells genetic material.

  3. Axon: The Axon also called Nerve Fiber; is a long, slender projection of a Neuron, its job is to conduct electrical impulses away from the neuron's cell body to transmit information to other cells.

  4. Glial: Glial cells are also known as Neuroglia, or Glia, are non-neuronal cells that maintain homeostasis, form myelin, and provide support and protection for neurons in the brain and peripheral nervous system.

  5. Axon Terminals: Axon Terminals, also called Synaptic Boutons, are distal terminations of the branches of an axon. An axon nerve fiber is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses, called Action Potentials away from the neuron's cell body, or soma, in order to transmit those impulses to other neurons.

  6. Dendrites: Dendrites are the branched projections of a neuron that act to propagate the electrochemical stimulation received from other neural cells to the cell body, or soma, of the neuron from which the dendrites project.

  7. Myelin and Myelin Sheath: Myelin is a fatty white substance that surrounds the Axon of some nerve cells, forming an electrically insulating layer. It is essential for the proper functioning of the nervous system. It is an outgrowth of a type of Glial cell. The Myelin wrapped around the Axon is called the Myelin Sheath.

  8. Nodes of Ranvier: The Nodes of Ranvier, also called Myelin Sheath Gaps, are the gaps (approximately 1 micrometer in length) formed between the myelin sheaths generated by different cells. A myelin sheath is a many-layered coating, largely composed of a fatty substance called myelin that wraps around the axon of a neuron and very efficiently insulates it. At nodes of Ranvier, the axonal membrane is uninsulated and therefore capable of generating electrical activity.

  9. Action Potential (AP): In order for a signal to travel along the axon of a nerve cell, a charge must build up across the axonal membrane. This spike in voltage is what is termed an Action Potential (AP). Creation of APs must be repeated many times at structures along the axon known as ion gates. However, with myelin sheaths insulating the axon an AP is observed to "jump" to the next ion gate which occurs at a neighboring Ranvier node. Thus, in myelinated axons, action potentials can "hop" along the axon, by which process the signal travels faster by skipping around the insulated sections.
  10. The action potential only moves in one direction, because the sodium channels, ion gates, at the previous node of Ranvier are inactivated, and cannot regenerate another action potential, even when depolarized. The charge will passively depolarize the adjacent node of Ranvier to the threshold, triggering an action potential in this region and subsequently depolarizing the next node, and so on.)

4. Sources

  1. U.S. National Library of Medicine. PubMed Health. Schwann Cells. https://www.ncbi.nlm.nih.gov/pubmedhealth/PMHT0025728/
  2. Linus Pauling Institute. Oregon State University. "Vitamin B12" (Retrieved January 2017) http://lpi.oregonstate.edu/mic/vitamins/vitamin-B12
  3. Linus Pauling Institute. Oregon State University. "Glossary" (Retrieved January 2017) http://lpi.oregonstate.edu/mic/glossary/
  4. Widemann, B. C., Acosta, M. T., Ammoun, S., Belzberg, A. J., Bernards, A., Blakeley, J., ... & Morrison, H. (2014). CTF meeting 2012: Translation of the basic understanding of the biology and genetics of NF1, NF2, and schwannomatosis toward the development of effective therapies. American Journal of Medical Genetics Part A, 164(3), 563-578. http://onlinelibrary.wiley.com/doi/10.1002/ajmg.a.36312/full
  5. Elsevier Health Sciences. Introduction to the Peripheral Nervous System. http://www.us.elsevierhealth.com/media/us/samplechapters/9781416031659/9781416031659.pdf
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