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What Is an Axon Membrane?

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  • Written By: Meg Higa
  • Edited By: Shereen Skola
  • Last Modified Date: 10 December 2016
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The typical nerve cell, also called a neuron, has distinct structural and functional parts. Its main body, called the soma, generates an electrical pulse. That signal travels through a long, thin extension called its axon. Just as a household electrical wire must be covered by an outer sleeve of insulation, the axon membrane functions as a protective sheath for the bio-electrical transmission. A chemically precise, healthy membrane is necessary for a fully functioning human brain and nervous system.

A single, microscopic axon thread in the human body can be short, but it can also be 4.9 feet long (1.5 meters) or more. At the other terminal end of an axon, the electrical signal discharges. It might release the energy to excite another neuron, to contract a muscle, or for any number of other bodily functions, including intelligent reasoning. In the case of passing along the signal to another neuron, the recipient cell body has small and short protrusions called dendrites. From axon to dendrites, the signal traverses a tiny gap between them called a synapse.

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Nerve cells have only one axon, and its electrical signal flows in only one direction. The axon can, however, split and branch repeatedly into numerous terminal ends. This is particularly important in the brain, where a single electrical impulse can stimulate multiple other neurons. The resulting cascade of branching terminal ends can be in the thousands. Further compounding the connections are “en passant” synapses in which the dendrites of other nerves latch onto the axon rod itself, not their terminal ends.

The structure and chemical properties of the axon membrane is what enables it to contain an electrical charge, to force its flow in one direction, and to transfer the signal to other cells of the body. For the most part, for most types of nerve cells, the axon is insulated within a protective sheath called myelin. This layer of the axon membrane is pinched at regular intervals called “nodes of Ranvier.” These gaps without myelin effectively amplify the incoming electrical signal, forcing its rapid one-way transmission. The signal is not a single uninterrupted wave; it pulses within the axon from node to node.

The integrity and health of the axon membrane are known to be one of the keys to debilitating neurological diseases, such as Multiple Sclerosis (MS). MS is caused by the de-myelination of neural axons. Other disorders include temporary trauma to the myelin sheath called neurapraxia which blocks a nerve’s ability to conduct electricity and typically results in either loss of sensory feeling or muscle control of the affected area.

The axon membrane is necessarily designed to contain an electrical charge, to prevent its escape. Yet, this is what appears to happen at the terminal ends of an axon. Scientists studying the molecular structure of the membrane and the chemical composition of synapses now understand that the signal transfer is actually a chemical one. The electrical energy fuels changes in chemicals, particularly sodium and potassium, allowing them to cross the membranes through specialized hollow proteins called ion channels.

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