People with myasthenia gravis (MG) know firsthand that their muscles don’t always work the way they want them to. With myasthenia gravis, your muscles may become weak and cause problems with movement or vision. Why don’t muscles work correctly in myasthenia gravis? This article will help you understand how the nervous system sends messages to your muscles and why myasthenia gravis disrupts that process.

How Do Nerves Communicate With Muscles?

Your body’s central nervous system (CNS) acts as the communication headquarters for your muscles. The CNS, which comprises your brain and spinal cord, communicates through a network of cells that eventually make contact with your muscle cells.

Neurons

Neurons, sometimes called brain cells, are cells in your nervous system. They play a crucial role in the communication process from the central nervous system to the muscles. Neurons pass messages to each other at specific points known as synapses.

When you decide to move, these messages travel down from your brain to your spinal cord and then your muscles, similar to how a relay race works. Once these messages reach your spinal cord, they are then sent out to the muscles through nerve connections called neuromuscular junctions, where the nerves meet the muscles.

Synapses

Neurons have specialized structures that help them send and receive messages. The sender is the axon, and the receiver is the dendrite. Axons have vesicles (tiny bags) that are filled with chemicals called neurotransmitters. When two neurons talk, these chemicals are released from the axon into a small space between the neurons called the synaptic cleft. Here, they attach to specialized proteins on the other side, called the postsynaptic membrane.

These specialized proteins are receptors. When excitatory neurotransmitters attach to receptors, they allow the cell to become excited. Once the cell gets excited, it can pass the message to the next neuron.

Neuromuscular Junction

At the neuromuscular junction (NMJ), the presynaptic neuron is a specialized neuron called the motor neuron. The motor neuron makes a synapse directly with the parts of the muscle to excite it and help it contract.

The axon in the motor neuron releases a neurotransmitter called acetylcholine (ACh). Acetylcholine can then attach to acetylcholine receptors on the muscle to excite the muscle. This process causes the muscle to contract.

How Does Myasthenia Gravis Affect the Nervous System?

The immune system has evolved to identify and fight off foreign invaders like bacteria and viruses. This is our bodies’ defense system that is responsible for clearing out infections. In autoimmune conditions like myasthenia gravis, the immune system mistakenly recognizes parts of a person’s body as the foreign invader.

Antibodies

To attack viruses and bacteria, the immune system makes proteins called antibodies. Antibodies recognize a unique part of another protein and attach to that protein. Once the antibodies attach to that other protein, they act as a tag for the immune system to destroy the protein and cell.

Autoantibodies

In myasthenia gravis, the immune system makes antibodies against proteins in our body. These are called autoantibodies. Specifically, the autoantibodies bind to acetylcholine receptors. When antibodies bind to a receptor, they block its activity. When acetylcholine receptors at the NMJ don’t work properly, the muscles can’t contract.

Another autoantibody that is common in myasthenia gravis is against the muscle-specific kinase (MuSK) protein. These proteins work at the NMJ to help acetylcholine receptors work their best. When autoantibodies stop MuSK from working, this also stops the acetylcholine receptors from working. This then does not allow for the muscle to contract.

Symptoms

Myasthenia gravis symptoms such as muscle weakness result from autoantibodies blocking or hindering the work of acetylcholine receptors. Symptoms can affect muscles in the limbs. However, most myasthenia gravis cases primarily block the muscles in your eyes. Next in line for most common symptoms is facial weakness.

Face and eye symptoms might include:

• Droopy eyelids
• Difficulty swallowing, speaking, or moving your mouth
• Garbled speech
• Muted facial expression
• Double vision

Because myasthenia gravis can also affect other parts of your body, you could experience:

• Difficulty walking
• Trouble lifting your arms
• Muscle weakness in any other body part

Taking certain medications, such as statins and some antibiotics, can make these symptoms even worse.

Because you have muscles in your chest that help you breathe, you might have trouble breathing. Trouble breathing can be very serious and requires immediate medical attention. Additionally, it may also cause you not to get enough oxygen, leading to fatigue.

Do Treatments Improve Communication at the NMJ?

Treatments for myasthenia gravis work on targeting the cause of the condition: bad communication at the NMJ. Treatments can improve NMJ communication using different methods.

Creating More Acetylcholine

Some medications for myasthenia gravis work to accumulate more acetylcholine at the synapse. Medications called anticholinesterases stop the enzyme acetylcholinesterase from breaking down acetylcholine. The more acetylcholine there is, the likelier it is to find a receptor that isn’t blocked by autoantibodies. More contact with acetylcholine receptors allows your muscles to contract.

Stopping Autoantibodies

Some medications for myasthenia gravis target the autoantibodies. Immunosuppressive drugs can weaken your immune system so that it isn’t making as many antibodies. This strategy leads to less acetylcholine receptor blockage and less muscle weakness.

Removing the Source of the Autoantibodies

The thymus gland is an organ that makes the autoantibodies that create problems in myasthenia gravis. For some people with myasthenia gravis, removing the thymus gland in a surgery called a thymectomy can help relieve symptoms. Without the source of the autoantibodies, the muscles can work normally.

Talk to Your Doctor

Tell your doctor if you have new symptoms or if your symptoms have gotten worse. They will make sure you get the best treatment for your myasthenia gravis. Your doctor is the best person to ask for help, especially if something is not right.

Find Your Team

On MGteam, the social network for people living with myasthenia gravis and their loved ones, more than 1,000 members come together to ask questions, give advice, and share their stories with others who understand life with myasthenia gravis.

Do you or a loved one have myasthenia gravis? Are there any medications your doctor has advised you to avoid? Share your experience in the comments below, or start a conversation by posting on your Activities page.