Demyelination: Definition & Causes

Instructor: Amanda Robb

Amanda holds a Masters in Science from Tufts Medical School in Cellular and Molecular Physiology. She has taught high school Biology and Physics for 8 years.

In this lesson, you'll be learning about demyelination diseases. We'll look at how inflammatory diseases, such as multiple sclerosis, and viral infections can cause myelin degradation as well as the symptoms of this condition.

What Is Demyelination?

Imagine taking your phone charger out of your bag. The white plastic on the cable keeps it insulated from water and other problems. You place the cable on the table and then walk away to get a drink of water. When you return, your kitten has chewed through the white plastic. Luckily, she is fine since the cable wasn't plugged in, but what do you think will happen to the charger? It might still work, but not nearly as well as it used to. The plastic on the outside of the cable is not only used to protect the wires inside but also insulates the wire, keeping electricity flowing efficiently from the wall to your phone.

You might still be wondering how this relates to your body. All the cells in your nervous system, called neurons, run on electricity just like your phone. Your neurons receive chemical signals from the environment or other cells and transmit them electrically. Like wires, your neurons have insulation to keep the electric signals transmitting efficiently. This insulation is called myelin. Myelin is made of fat produced by supporting cells like Schwann cells and oligodendrocytes.

Supporting cells secrete myelin to keep signals running smoothly between neurons

Myelin is important to keep our nervous system running smoothly. Without myelin, the electrical signals dissipate into the surrounding area and are not conducted properly. Some people develop diseases where their myelin starts to degrade, called demyelination.

Demyelination causes communication problems between the brain and body. The brain may not be able to control body movement or functions, and the person may not be able to sense their environment normally, since messages are lost from sensory organs on the way to the brain.

So, what causes demyelination? The main cause is a disease called multiple sclerosis, although other other inflammatory diseases as well as viruses can also cause demyelination. Let's look at each of them in detail next.

Inflammatory Diseases

Inflammation can be a normal part of healing, such as how a cut turns red and swells when you are injured. However, with inflammatory diseases, the immune system attacks the body, causing parts of the body to become injured.

Multiple Sclerosis (MS)

John, a new patient, comes to your office complaining of weakness and numbness in his legs. He's been feeling dizzy lately and sometimes catches himself slurring his speech.

One of John's family members has multiple sclerosis, and John is concerned that his symptoms might be caused by the disease. As a concerned medical professional, your first step is to do a neurological exam and follow up with scans of the brain.

Multiple sclerosis (MS) is the most common demyelinating disease. It is caused by genetics and triggered by environmental factors. In this disease, the immune system attacks the myelin sheath on neurons in the brain and spinal cord. Symptoms may be mild, such as John's, or they can be extremely debilitating resulting in paralysis.

Symptoms of multiple sclerosis
symptoms of MS

Acute Disseminated Encephalomyelitis (ADEM)

A mother brings her child in to see you. Recently Harold has had an upper respiratory tract infection and a high fever. The fever has persisted, but now he is experiencing neurological symptoms like confusion, drowsiness, and weakness in his extremities. These symptoms are characteristic of a rare demyelinating disease called acute disseminated encephalomyelitis (ADEM).

Usually occurring in children, the disease typically follows some sort of infection, making it different than the purely autoimmune problems associated with MS. After the infection, the immune system mounts a strong response, which ends in demyelination. Luckily, most of these patients will recover with treatment of the infection.

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