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What is a Neuromuscular Junction?

Mary McMahon
Updated Mar 03, 2024
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A neuromuscular junction is a place in the body where the axons of motor nerves meet the muscle, allowing them to transmit messages from the brain that cause the muscle to contract and relax. Every organism has thousands of these junctions that control the movements of the body and cause the heart to beat. It is only one example of many connections made between nerves and other parts of the body that result in a successfully functioning organism.

Neurons, or nerve cells, are specially designed cells that communicate using chemicals called neurotransmitters. Depending on the type of cell, specific neurotransmitters are designed to stimulate a response, assuming that a receptor is present. In addition to a body, neurons also have a long tail called an axon that terminates in dendrites, a bundle of fibers that can transmit chemicals to the next neuron. In the instance of a neuromuscular junction, one neuron can control many muscle cells, but each muscle cell only responds to one neuron.

At this junction, the motor neuron meets muscle tissue at an axion terminal. The surface of the muscle fiber forms small ridged folds for the end of axon to rest in. Inside these folds are depressions with acetylcholine receptors. The neuron forms synaptic vesicles that are filled with acetylcholine. They resemble small bulbs that will release the neurotransmitter when the muscle needs to contract.

The neuromuscular junction is crucial for life, and they begin forming early in fetal development. As motor neurons develop, a protein called agrin is made. This stimulates the formation of a muscle specific kinase, which will build receptors for acetylcholine on the surface of the muscle fiber. This is how the junction is formed, with the neuron itself emitting the needed chemical for development.

Several conditions can cause malfunctions at these sites, leading to loss of muscle control. Ultimately, lack of muscle control can cause death if it is severe, because the body's largest muscle, the heart, could stop beating. The most common such illness is myasthenia gravis, which is caused by an autoimmune reaction against acetylcholine receptors. As a result, motor neurons cannot transmit the chemical to the muscles, which will cause muscle weakness and an ultimate loss of control.

Myasthenia gravis tends to be more concentrated along skeletal muscles and is especially noticeable in the face. Additionally, some toxins, such as botulinum, will inhibit the release of acetylcholine, which will lead to muscle paralysis.

The Health Board is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Mary McMahon
By Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a The Health Board researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Discussion Comments

By anon34433 — On Jun 22, 2009

Overall this is an acceptable answer. However, neurons do not cause the hearts of all species to beat (ie from frogs to humans). Each heart beat is generated by specialized heart cells (sinoatrial nodal cells) that generate there own spontaneous active. Rather, the nerves regulate the frequency of beating.

By anon30539 — On Apr 20, 2009

Describe the factors that lead to a muscle contraction, from the neuron to the neuro-muscular junction, what is happening at each part within the muscle cell and its organelles, leading to contraction in the muscle cell fibers.

Mary McMahon

Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a...

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