Etiology and Pathophysiology

MS is a chronic inflammatory demyelinating and neurodegenerative disease of the CNS which inhibits conduction of nerve impulses. In the CNS, the myelin sheath is a membranous extension of specialized cells called oligodendrocytes. These membranous extensions form a barrier that insulate and support and nerve axons of the brain and spinal cord.

The velocity or speed of impulse transmission is faster through myelinated axons. Non-myelinated axons conduct impulses very slowly. Healthy myelinate nerves can conduct impulses 50 times faster than non-myelinated nerves. MS causes axons to lose their covering of myelin, a process known as demyelination. Demyelination disables axons, making them unable to conduct stimuli rapidly or effectively.

"MS lesions evolve differently during early versus chronic disease phases, and within each phase, different plaque types and plaques in different stages of demyelinating activity are evident. Histologically, several basic processes drive the formation of plaques: inflammation, myelin breakdown, astrogliosis, oligodendrocyte injury, neurodegeneration and axonal loss, and remyelination" (Popescu B. 2013).

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Axons not covered by myelin transmit nerve impulses more rapidly than myelinated axons.

The etiology of multiple sclerosis (MS) remains unknown but multiple factors have been identified: immune dysfunction, genetic predilection, environmental factors and infectious agents.

Immune system connection:

Genetics (NMSS)

Environment (healthline)

Epidemiologists have seen an increased pattern of MS cases in countries located farthest from the equator. People who live near the equator are exposed to more ultraviolet B radiation, This correlation causes some to believe that vitamin D may play a role. Vitamin D benefits immune system function.

Infection (NMSS)

"Many viruses and bacteria — including measles, canine distemper, human herpes virus-6, Epstein-Barr virus (EBV), and Chlamydia pneumonia — have been or are being investigated to determine if they are involved in the development of MS.  EBV, the virus that causes mononucleosis, has received significant attention in recent years. A growing number of research findings indicate that previous infection with EBV contributes to the risk of developing MS."

Instant Feedback:
The myelin sheath surrounding the axons in the peripheral nervous system is the site of damage in MS.


healthline. 4 Possible Causes of Multiple Sclerosis (MS). Retrieved 11/9/2019.

Popescu, B. F., Pirko, I., & Lucchinetti, C. F. (2013). Pathology of multiple sclerosis: where do we stand?. Continuum (Minneapolis, Minn.), 19(4 Multiple Sclerosis), 901–921

National Multiple Sclerosis Society (NMSS) Retrieved 11/9/2019