How MS Affects the Brain Stem

The Impact of Injury to the Brain's Communication Center

Section through a human brain
Cross-section of the cerebrum, cerebellum, and brain stem. Science Picture Limit/Science Photo Library/Getty Images

The brain stem is a stem-like extension at the base of the brain which connects the brain to the spinal cord. It serves as the communications center of the brain and coordinates where electrical nerve impulses are delivered throughout parts of the body.

Multiple sclerosis (MS) is characterized by the formation of lesions (also known as plaques) on parts of the central nervous system. Depending on where the plaques are located, nerve transmissions may be interrupted, causing the array of neurological symptoms we associate with MS.

How the Brain Stem Work

Think of you brain stem as the control terminal in a vast, wired communications network. As messages are sent from the brain, they pass through the brain stem in the form of electrical impulses. It is here that the impulses are directed to individual substation—known as the medulla oblongata, the pons, and the midbrain— each of which oversees the regulation of specific autonomic (involuntary) and somatic (voluntary) functions.

From this junction, the impulses are relayed to the spinal cord via a network of nerve cells, known as neurons. Each neuron is interconnected by thread-like fibers, called axons, which deliver the transmitted message to the specific motor or sensory system.

Parts of the Brain Stem

The brain stem, while small, serves a massive purpose. It is responsible for conducting all communications from the cerebrum (the main portion of the brain) and cerebellum (often referred to as the "mini-brain") to the rest the body.

It comprises 10 of the 12 nerves, known as cranium nerves, that service the head, face, and internal organs. Moreover, it regulates the basic physiological and sensory systems that we need to function and stay alive.

The brain stem is broken down into three parts:

  • The medulla oblongata, located in the lower portion of your brain stem, is central to the regulation of your heart rate and blood pressure.. It also coordinates involuntary reflexes such as coughing, sneezing, and vomiting.
  • The pons is situated in the middle part of the brain stem and is responsible for regulating breathing and deep sleep. It is also involved in sensations associated with hearing, taste, and balance.
  • The midbrain, also known as the mesencephalon, is located at the top end of the brain stem and is responsible for nerve transmissions central to sight, sound, and body movement. It also regulates autonomic functions such as digestion, heart rate, and breathing rate.

In addition, within these three regions is a dense network of nerve pathways, called the reticular formation, which regulate your overall consciousness level.

How MS Affect the Brain Stem

While the cause of multiple sclerosis is not entirely clear, it believed to be either an autoimmune disorder (in which immune cells attack normal, healthy cells) or an immune-mediated disorder (in which inflammation from an abnormal immune response causes cellular damage).

In either case, MS is considered a demyelinating disease which strips away the protective coating of neurons, called the myelin sheath. When this happens, the neurons begin to malfunction while the lines of communications between cells are disrupted. The progressive damage caused by demyelination leads to scarring of nerve tissue in the form of plaques.

Symptoms of Brain Stem Injury

Plaques can develop anywhere in the central nervous system, but when they do so on the brain stem, any number of functions can be impaired. These include:

  • Vision impairment, including double vision or jerky eye movements
  • Motor impairment, including a loss of motor control or limb weakness
  • Hearing impairment, including deafness, tinnitus, or noise intolerance
  • Speech impairment, including slurred speech and irregular speech patterns
  • Loss of sensations, including taste, smell, or skin sensations
  • Loss of balance or vertigo
  • Loss of fine movement, including writing or typing skills
  • Abnormal emotional responses, including inappropriate crying or laughing
  • Swallowing problems, including choking, coughing, or gagging

The extent of plaque involvement can usually be diagnosed with a magnetic resonance imaging (MRI) scan. While the reversal of nerve damage is difficult, research has begun to show promise in promoting the remyelination through the use of immunological antibodies, stem cell transplants, and nerve-protecting drug agents.

Source: 

Lublin, F.; Reingold, S.; Cohen, J. et al. "Defining the clinical course of multiple sclerosis: The 2013 revisions." Neurology. 2014; 83(3):278-286.

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