MSFrontier

What is multiple sclerosis?

Multiple sclerosis (MS) is a long-term condition affecting the brain and spinal cord. Damage to the protective covering of nerve fibres and to the fibres themselves can disrupt communication within the nervous system.
Module 1 · Lesson 1 of 2 · 3 min · Interactive · Sources checked October 2026 · Not yet reviewed by an MS specialist
Clay illustration for What is multiple sclerosis?

The brain, spinal cord and myelin

The brain and spinal cord form the central nervous system. Myelin is a covering around nerve fibres that helps signals travel efficiently. MS damages myelin and can also damage the underlying nerve fibres. Symptoms depend in part on which areas are affected.

Illustrative physical model showing a nerve fibre surrounded by segmented myelin covering
Illustrative myelin model, generated for this publication. Not microscopy or patient data. The anatomy is described by NINDS.[1]
MyelinAxon (nerve fibre)
Myelin lets the signal jump quickly from gap to gap.

Why symptoms differ

MS can affect movement, vision, sensation, balance and thinking, and fatigue is common. A list of possible symptoms is not a checklist for diagnosing MS: other conditions can cause similar problems.

Some people experience relapses followed by periods of recovery. Others have progressive worsening from the outset, or develop progression after a relapsing course. These descriptions do not predict an individual person’s future.

What causes MS?

The exact cause is not fully understood. MS involves an abnormal immune response, with genetic susceptibility and environmental factors contributing to risk. A family history does not mean that a person will develop MS.

Long-term studies point to the Epstein-Barr virus (EBV) as a major cause. Infection alone is not enough to cause MS, and how the virus leads to the disease is still being worked out.

Treatment and care have different goals

There is no cure yet. Relapsing MS can now often be well controlled, and research is working on progression and repair. Medicines that change the course of the disease, treatment for relapses, treatment for symptoms and rehabilitation each have a different purpose, and how much they help depends on the person and on the course of their MS.

Animation: a nerve signal jumps quickly along intact myelin and slows where myelin is damaged. Illustrative, not to scale.Intact myelinMyelin lostsignal jumps from node to nodesignal spreads slowly, and arrives weakened
Figure 1. Animation: a nerve signal jumps quickly along intact myelin and slows where myelin is damaged. Illustrative, not to scale.[1]
Left: a nerve fibre with intact myelin. Right: the same fibre after demyelination, with immune cells nearby. Illustration.
Figure 2. Left: a nerve fibre with intact myelin. Right: the same fibre after demyelination, with immune cells nearby. Illustration.[1][2]
Immune cells cross the wall of a blood vessel into the brain and reach myelinated nerve fibres. Illustration.
Figure 3. Immune cells cross the wall of a blood vessel into the brain and reach myelinated nerve fibres. Illustration.[1]

In more depth

More than loss of insulation

Demyelination means loss or damage of myelin. MS also involves inflammation and injury to axons, the fibres that carry nerve signals. Damaged areas are often called lesions or plaques. The wiring analogy helps explain signal disruption, but it does not capture the full biology of inflammation, nerve injury and repair.

Disease course is not a biological boundary

Clinical course labels describe patterns over time. They are not separate diseases with entirely separate mechanisms. Relapse activity and disability progression are distinct dimensions, and progression can matter even in a disease course described as relapsing.

Common questions

Is MS directly inherited?

No. Genetic susceptibility contributes to risk, but MS does not follow a simple pattern of direct inheritance. Family history is one factor, not a diagnosis or a prediction.[1][2]

Does everyone have the same symptoms?

No. The symptoms and course vary between people, and can change over time.[1][2]

Is there a cure?

Not yet. Treatments and rehabilitation can help with disease activity, symptoms or function, but these are not the same as a cure.[1][2]

In the research now

Loading current research…

Key terms

Myelin
The fatty sheath wrapped around many nerve fibres in the brain and spinal cord. It lets signals jump quickly along the fibre. MS damages it.
Axon (nerve fibre)
The long extension of a nerve cell that carries its signal. Losing axons, rather than myelin alone, is thought to cause most lasting disability.
Lesion (plaque)
An area of damage where myelin has been lost and the tissue scarred.
Relapse (attack)
New or worsening symptoms lasting at least 24 hours, without fever or infection to explain them.
Epstein-Barr virus (EBV)
A common herpes virus that causes glandular fever. Infection appears to be almost necessary for MS, but most infected people never develop it.

References

  1. NINDS · Multiple sclerosis ↗

    Medical reference

  2. NHS · Multiple sclerosis ↗

    Medical reference

  3. Lublin et al. · Defining the clinical course of multiple sclerosis: the 2013 revisions (2014) ↗

    Consensus

  4. Bjørnevik et al. · Longitudinal analysis of Epstein-Barr virus and MS (2022) ↗

    Primary research

Next · Lesson 2 of 2

Myelin, axons and the cells that make them

Signals in the brain and spinal cord travel along nerve fibres wrapped in myelin. This lesson explains how that wrapping works, why the fibre underneath depends on it, and what happens to both in MS.

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