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The neuromuscular junction is where motor nerves meet muscles to transmit messages from the brain, controlling body movements and heartbeats. Neurons communicate using neurotransmitters and have axons that transmit chemicals to the next neuron. Malfunctions can cause muscle weakness and loss of control, as in myasthenia gravis.
A neuromuscular junction is a point 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 body movements and make the heart beat. It is just one example of the 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 cell type, specific neurotransmitters are designed to elicit a response, assuming a receptor is present. In addition to a body, neurons also have a long tail called an axon that ends in dendrites, a bundle of fibers that can transmit chemicals to the next neuron. In the case 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 in which the end of the axon can rest. Within these folds are depressions with acetylcholine receptors. The neuron forms synaptic vesicles which are filled with acetylcholine. They look like little bulbs that will release the neurotransmitter when the muscle needs to contract.
The neuromuscular junction is crucial to life and begins to form early in fetal development. As motor neurons develop, a protein called agrin is produced. This stimulates the formation of a muscle specific kinase, which will build acetylcholine receptors on the surface of the muscle fiber. This is how the junction is formed, with the neuron itself emitting the chemical needed for development.
Several conditions can cause these sites to malfunction, leading to loss of muscle control. Ultimately, lack of muscle control can lead to death if it’s severe, because the largest muscle in the body, the heart, may stop beating. The most common of these diseases is myasthenia gravis, which is caused by an autoimmune reaction against acetylcholine receptors. As a result, the motor neurons cannot transmit the chemical to the muscles, which will cause muscle weakness and a permanent loss of control.
Myasthenia gravis tends to be more concentrated along the skeletal muscles and is particularly evident on the face. Additionally, some toxins, such as botox, will inhibit the release of acetylcholine, which will lead to muscle paralysis.
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