Amyotrophic lateral sclerosis (ALS) is a degenerative neurological disorder that involves the death of nerve cells in the brain and spinal cord. This, over time, leads to the brain losing its ability to control voluntary movements, resulting in symptoms such as difficulty walking, speaking, and eating, eventually leading to paralysis.

Doctors are unsure of the exact causes of ALS and of the mechanisms that underlie the disease, but they know that it affects cells called motor neurons. These components of the nervous system are responsible for controlling voluntary and involuntary movements throughout the body. As ALS advances, these motor neurons deteriorate and die, leading to a progressive loss of muscle control.

This article will explain how ALS affects the brain and the body in general. It will also detail its causes, treatment, and outlook.

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ALS affects the brain, as well as various other parts of the body. Doctors classify it as motor neuron disease (MND), a group of progressive neurological disorders. This is because ALS affects components of the nervous system known as motor neurons that control voluntary movements, such as walking and speaking. These specialized cells reside in the brain and spinal cord.

ALS may begin with issues in the upper or lower motor neurons, which reside in different parts of the body.

  • Upper motor neuron disease: These originate in the brain, causing stiffness or spasticity.
  • Lower motor neuron disease: These originate in the spinal cord, causing weakness, muscle loss, and muscle twitching.

A person may have varying amounts of upper and lower motor neuron disease.

Read more about ALS here.

The underlying mechanisms of ALS are complex and not fully understood. In general, ALS causes degeneration of both upper and lower motor neurons in the brain and spinal cord, ultimately leading to the death of these cells. The brain cannot initiate and control muscle movement when motor neurons die.

What are motor neurons?

Motor neurons are the longest cells in the body. Some motor neurons in the spinal cord must extend their axon, or long nerve fiber, up to a meter to reach the muscles in the toes. Correspondingly, the metabolic demands on these cells are extraordinary.

Active transport of cellular material along the length of motor neurons is critical for the overall health of the cells and to keep communication flowing. Because of their length, motor neurons may be particularly vulnerable to genetic abnormalities or cellular issues affecting this transportation process. Therefore, experts believe that malfunctions within this system contribute to ALS.

Excess glutamate

There are also other potential contributing factors, including the neurotransmitter glutamate. If there is too much glutamate, it results in prolonged stimulation of the motor neuron. Evidence points to glutamate as a destructive factor in ALS.


Inflammation is also involved in ALS. Neuroinflammation, which is inflammation in the central nervous system, appears to accompany motor neuron death in ALS. Research is ongoing to better understand the neuroinflammatory process and its involvement in this disease.

ALS does not directly affect the body’s organs other than the brain and spinal cord. However, the disease’s effects are widespread due to its impact on the muscles, which can lead to difficulties in speaking, eating, breathing, and moving.


ALS causes various physical problems as it progresses. People with ALS may experience:

  • difficulty standing
  • issues with walking
  • trouble speaking
  • difficulty swallowing

As a result, they may have trouble eating, causing them to lose weight and become malnourished.

Muscle cramps and nerve damage can be painful and cause twitching. Spasticity, which is excessive tightness or stiffness in the muscles, can make movement difficult.

As the condition worsens, people become increasingly paralyzed and lose control of their arms, legs, and, eventually, the muscles necessary for breathing.

Learn about the stages of ALS here.


Previously, ALS was thought to cause physical symptoms only and leave the mind unaffected. But research now shows that people with ALS have various cognitive and behavioral problems.

For example, they may demonstrate:

  • apathy or a loss of sympathy
  • changes in their eating behaviors
  • a lack of inhibition

People with ALS affecting the bulbar region of the brain appear more likely to have these issues.

Some people with ALS may develop a form of dementia and have trouble with their language and decision-making.

ALS can also trigger mental health issues, such as depression and anxiety. These problems may arise as people have difficulty coming to terms with their diagnosis and its implications.

ALS is progressive, so early symptoms are usually mild and include:

  • muscle twitches or cramps
  • muscular stiffness or weakness
  • speech issues
  • difficulty chewing or swallowing

As ALS progresses, symptoms worsen, and a person may have difficulty:

  • standing and walking
  • chewing and swallowing
  • speaking or forming words
  • maintaining their weight
  • breathing

ALS is a motor neuron disease that causes motor neurons to degenerate and die. As a result, the muscles stop receiving signals from the nerves, leading to muscle weakness, involuntary movements, and, eventually, paralysis.

Scientists are currently unsure why this happens to some people, but they have identified several risk factors, including:

  • Age: ALS most commonly affects those between the ages of 55 to 75.
  • Biological sex: Males are slightly more likely to develop ALS, but this gender difference disappears as people age.
  • Race: Caucasians and non-Hispanics are more likely to have ALS than other racial and ethnic groups.
  • Family history: Although most instances of ALS are sporadic, about 5 to 10% of all people with ALS have inherited it. Experts have found mutations in more than a dozen genes that cause familial ALS.
  • Military status: Veterans are about as much as two times more likely to develop ALS, although experts are not clear why this is. It is potentially due to exposure to lead, pesticides, and other toxins while serving.

ALS is a difficult disease for doctors to diagnose. There is no one test to confirm a diagnosis, so instead, doctors must use a series of tests to rule out similar conditions.

A thorough diagnostic workup typically includes:

  • electrodiagnostic tests, including electromyography (EMG) and nerve conduction velocity (NCV)
  • blood and urine studies
  • a spinal tap
  • X-rays and other imaging studies
  • muscle and nerve biopsies
  • neurological examinations

Read more about testing for ALS here.

Various medications and therapies can make living with ALS easier. However, no treatment can reverse nerve damage or cure ALS.

  • Riluzole: Doctors may prescribe riluzole (Rilutek) to reduce nerve damage. It decreases glutamate levels, a chemical that transports messages between nerve cells and motor neurons, and it can increase life expectancy by several months.
  • Edaravone: Other options include edaravone (Radicava), an intravenous drug that slows the progression of ALS by preventing nerve damage. Doctors can also prescribe medications to help with pain, muscle cramps, or mental health issues.

Besides medications, nutritional and physical therapy can help people stay as comfortable, independent, and active as possible. Physical therapists can provide people with exercises to maintain muscle strength, mobility aids to increase independence, and even breathing techniques to improve ventilation.

Occupational therapists may suggest assistive devices, such as computer programs or speech-generating devices, that make communication easier.

There is no known cure for ALS, and symptoms can develop quickly. It is important to recognize that everyone is unique, but most experience disease progression within 5 years of diagnosis. Yet, some individuals can live for decades. Around 1 in 5 people living with ALS survive more than 5 years, while around 1 in 20 live for 20 years or more.

Advances in treatments have created new hope for those affected by ALS. Treatment options can help slow the disease’s progression, improve a person’s quality of life, and potentially lengthen a person’s life expectancy.

Amyotrophic lateral sclerosis is a motor neuron disease that affects the nerves in the brain and spinal cord. It causes muscle weakness, movement problems, and eventual paralysis.

The cause of ALS is still unknown, but experts have identified several risk factors, including age, sex, race or ethnicity, family history, and military status. Diagnosis involves a series of tests to rule out similar conditions.

Medications and therapies can help people with ALS manage their symptoms and optimize their quality of life. However, ALS has no cure.