What ALS does to nerve cells

ALS kills the nerve cells that control your muscles. These nerve cells, called motor neurons, sit in your brain and spinal cord and send signals down to your muscles telling them to move. In ALS, something goes wrong and the body's immune system attacks these cells, or they simply stop working and die. As more motor neurons die, your muscles get weaker because they stop receiving the signals they need to contract.

The damage happens gradually. Early on, you might notice weakness in one hand or foot, or your speech might become slurred. Over time, the weakness spreads to other parts of your body. The muscles themselves are not diseased—they are just not getting the signal to work anymore. If a muscle does not get that signal for long enough, it shrinks and becomes permanently weak.

Key Takeaways

  • ALS destroys motor neurons in the brain and spinal cord, which are the nerve cells that tell muscles to move.
  • As these nerve cells die, muscles gradually weaken and eventually stop responding to commands from the brain.
  • The disease usually starts in one area—a hand, foot, or the mouth—and spreads over months or years.
  • Most people with ALS eventually lose the ability to walk, use their hands, and speak, and breathing becomes harder as the diaphragm weakens.
  • ALS does not affect sensation, memory, or thinking ability in most people, even as physical abilities decline.

How weakness spreads through the body

ALS does not strike all muscles at once. It usually begins in one region—the hands and forearms, the feet and lower legs, or the muscles that control speech and swallowing. From there, it spreads to nearby muscle groups over weeks or months. A person might notice they drop things or trip more often, or that their words become harder to understand.

The pattern of spread varies from person to person. Some people experience what doctors call bulbar onset, meaning the disease starts in the muscles of the mouth and throat. Others have limb onset, starting in an arm or leg. Regardless of where it begins, the weakness eventually reaches the diaphragm—the muscle that controls breathing. This is the most serious stage of the disease.

Loss of movement and independence

As ALS progresses, everyday tasks become harder. Writing, buttoning a shirt, holding a fork, and walking all require the motor neurons that ALS destroys. Over time, a person may need a cane or walker, then a wheelchair. They may need help with personal care, eating, and dressing.

The speed of this decline varies widely. Some people lose physical abilities over two to five years. Others progress more slowly, over ten years or more. There is no way to predict how fast any individual will decline. This unpredictability is one reason why people with ALS often work with occupational and physical therapists early on—to learn adaptive techniques and plan for equipment they may need later.

Breathing and swallowing problems

Two of the most serious effects of ALS involve muscles you do not usually think about: the diaphragm and the muscles of the throat. As the diaphragm weakens, breathing becomes harder, especially when lying down or during sleep. A person may wake up gasping or feel short of breath during the day. Eventually, most people with ALS need a ventilator—a machine that breathes for them—to stay alive.

Swallowing also becomes difficult as throat muscles weaken. Food or liquid may go down the wrong pipe into the lungs instead of the stomach, a problem called aspiration. This can lead to pneumonia. Many people with ALS eventually need a feeding tube placed directly into the stomach so they can receive nutrition without the risk of aspiration.

What ALS does not affect

It is important to know what ALS does not do. The disease does not damage the nerve cells that carry sensation, so a person with ALS can still feel touch, temperature, and pain. It does not affect the brain cells involved in thinking, memory, or reasoning in most cases. Most people with ALS remain mentally sharp throughout the disease, even as their bodies become paralyzed.

This is one of the hardest aspects of ALS for many people: being fully aware of what is happening to them while losing the physical ability to move or speak. Some people with advanced ALS use eye-tracking technology or other communication devices to continue expressing their thoughts and wishes.

Muscle wasting and fatigue

As motor neurons die, the muscles they controlled begin to shrink—a process called atrophy. Muscles that are not receiving signals from the brain cannot maintain their size or strength. Over time, this wasting becomes visible: arms and legs become noticeably thinner, and the body loses weight even when a person is eating enough calories.

Many people with ALS also experience fatigue that goes beyond normal tiredness. The remaining healthy motor neurons work harder to compensate for the dead ones, which uses more energy. This can make even small physical tasks exhausting. Fatigue often worsens as the disease progresses and fewer motor neurons remain to do the work.

Emotional and cognitive changes

Some people with ALS experience changes in mood or emotional control that are separate from the sadness or frustration that naturally comes with the disease. A condition called pseudobulbar affect can cause sudden, uncontrollable laughing or crying that does not match what the person is actually feeling. This happens because ALS damages the nerve pathways that regulate emotional expression, even though the person's actual emotions are intact.

In a small number of cases, ALS can affect thinking and decision-making in ways similar to dementia. This is more common in people who also have a family history of frontotemporal dementia. Most people with ALS, however, maintain full mental clarity throughout their illness.

Frequently Asked Questions

Does ALS cause pain?

ALS itself does not damage the nerves that carry pain signals, so the disease itself is not painful. However, people with ALS often experience muscle cramps, stiffness, and pain from immobility or from the strain of compensating with weaker muscles. Pain management is an important part of ALS care.

Can ALS stop progressing?

ALS is a progressive disease, meaning it continues to worsen over time. There is currently no cure, though some medications can slow the rate of decline slightly. The disease does not go into remission or reverse on its own.

Will I lose my mind with ALS?

In most cases, no. ALS affects the motor neurons that control movement, not the brain cells involved in thinking and memory. Most people with ALS remain mentally sharp. A small percentage experience cognitive changes, but this is not the typical course of the disease.

How long does it take for ALS to affect breathing?

This varies greatly. Some people experience breathing problems within a year or two of diagnosis, while others may not need breathing support for many years. The diaphragm is usually affected later in the disease, though the timeline is different for each person.

Can ALS affect both sides of the body equally?

ALS usually starts on one side and spreads, but over time it typically affects both sides. The weakness may remain stronger on one side than the other, but most people eventually experience weakness throughout their body as the disease progresses.