In the process of neuromuscular transmission, nerves send a signal to muscle fibers to trigger movement and relaxation. This occurs at a site known as the neuromuscular junction, because it forms the point of connection between the nervous system and the muscle fibers. Disorders of neuromuscular transmission can result in conditions like partial paralysis and muscle weakness. It is also possible to induce delays or halts in transmission with medication for activities like medical procedures.
This process starts with a signal that travels the length of the nerve, causing the nerve to release acetylcholine into the neuromuscular junction. The neurotransmitter reacts with receptors in the muscle and quickly dissipates. It is metabolized within the body for recycling to make more acetylcholine, providing a continuous renewal of the chemical. Rapid delivery and processing allow for very fine-grained control, as the nerve can quickly recover and release more for sustained muscle activity, or stop transmitting if the desired goal has been accomplished.
For any given movement, neuromuscular transmission may occur along the length of a muscle, and can involve the coordination of several muscles with asymmetrical releases of acetylcholine. These include conscious movements, like the decision to open a door to enter a room, as well as unconscious movements like reflexive reactions. When the knee is struck at the right angle, for example, it triggers a very fast reflex response that ends with neuromuscular transmission to make the leg kick out.
One potential disorder involving this process is called myasthenia gravis. This was among the earliest neuromuscular disorders identified and studied, and research into the subject provided important information about how neuromuscular transmission worked. This became important not just for the treatment of disease, but also for the development of neuromuscular blocks. In a block, medications can temporarily halt signal transmission to induce paralysis. Paralytic medications are used in procedures like surgery to protect patient safety.
Another useful tool for studies on neuromuscular transmission has been the use of knockout studies in mice. In a knockout study, researchers “knock out” a given gene, stopping the expression. This allows them to find out what the gene does, and how organisms adapt when it is no longer functional. Since mouse physiology is similar to that of humans when it comes to neuromuscular transmission, studying diseases in mice can offer insight into how to effectively treat humans. Controlled genetic research with knockout studies can help researchers pinpoint exactly which genes do what.