What is myelin sheath?
A typical nerve consists of dendrites, axons, a cell body, terminal buttons and myelin sheaths. Dendrites gather information from the environment and the stimulus is gathered in the cell body. The axons of a nerve function to carry nerve impulses from the body to another nerve. Spaces in between myelin sheaths in axons, where electrical impulses travel, are called Nodes of Ranvier.
The myelin sheath, also called medullary sheath, is a modified plasma membrane formed by layers of Schwann’s cell membranes (in the peripheral nervous system) or oligodendrocyte membranes (in the central nervous system) wrapped around the axon of the nerve. It is made up of lipids and proteins. Lipids constitute approximately 70% to 85% present in different forms such as cholesterol, cerebroside, ethanol-containing plasmogens, lecithin and sphingomyelin. Proteins compose approximately 15%-30% of the myelin sheath in the form of myelin basic protein and proteolipid protein. The myelin sheath is the part of the nerve damaged by the immune system in Guillain-Barre Syndrome.
Figure 1.0 Structure of a typical myelinated neuron
What is the importance of myelin sheath in nerve conduction?
Myelin sheath is composed mainly of fat (lipids) which are good electric insulators. This property of lipids gives myelin sheath its major function, that is, insulation of electrical impulses along the axon. Because of the insulation function of the myelin sheath, electrical impulses can’t travel along the myelinated parts of the axon and jump only from one node of Ranvier to another instead of traveling the entire span of the axon. This causes electrical impulses to travel at a more rapid rate as fast as the speed of a race car (70-120 m/s)....
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It was the beginning of February when my grandfather was going in to receive his second knee replacement. Being his second time, we were optimistic that the surgery would go well and that he would recover without any issues. My grandfather made it through surgery and accordingly, had to stay for observation. During this time everything appeared to be normal, and knowing that my grandfather hates to be in hospitals, wouldn’t have said otherwise. When he was finally discharged, we took him home and the next day he appeared to have a stroke. The left side of his face had drooped down and he began feeling numbness and tingling on both sides of his body. We immediately rushed him to the hospital and at first it was assumed it was a stroke, but as his illness progressed it was apparent it was not. The numbness soon led to the loss of muscle control beginning at his legs and rapidly spreading up. My grandfather was able to specifically describe what he was experiencing and the doctor was able to diagnose him with Guillain- Barré syndrome.
pathophysiology of the disease starts when the myelin sheath of both the spinal and cranial
Multiple sclerosis (MS) is a disease affecting the myelination of the central nervous system, leading to numerous issues regarding muscle strength, coordination, balance, sensation, vision, and even some cognitive defects. Unfortunately, the etiology of MS is not known, however, it is generally thought of and accepted as being an autoimmune disorder inside of the central nervous system (Rietberg, et al. 2004). According to a study (Noonan, et al. 2010) on the prevalence of MS, the disease affects more than 1 million people across the world, and approximately 85% of those that are affected will suffer from unpredictably occurring sessions of exacerbations and remissions. The report (Noonan, et al. 2010) found that the prevalence of MS was much higher in women than in men, and that it was also higher in non-Hispanic whites than in other racial or ethnic groups throughout the 3 regions of the United States that were studied.
Canavan disease is an inherited disorder that causes progressive damage to the nerve cells in the brain. It is in the group of rare genetic disorders called Leukodystrophies. Leukodystrophies are characterized by the degeneration of myelin, which is the fatty covering that insulates nerve fibers. The myelin is necessary for rapid electrical signals between the neurons. I chose this disease because I had never heard of it and it seems to only affect a very small amount of people. Also it isn’t very common so I wanted to learn more about it, which helped when looking for information
Lou Gehrig's disease is often referred to as Amyotrophic lateral sclerosis (ALS), this is a progressive neurodegenerative disease that affects nerve cells in the brain and the spinal cord. Motor neurons come from the brain to the spinal cord and from the spinal cord to the muscles throughout the entire body. The progressive degeneration of the motor neurons in ALS would eventually leads to their death. When the motor neurons die, the ability of the brain to initiate and control muscle movement is also lost. With voluntary muscle action progressively affected, for this reason patients in the later stages of the disease may become totally paralyzed (Choi, 1988).
Multiple sclerosis (MS) is generally thought to be an autoimmune disease that attacks the myelin sheaths, or oligodendrocytes that cover nerve axons in the central nervous system (PubMed Health 2013). This immune response causes inflammation, which triggers immune cells to destroy axons “along any area of the brain, optic nerve, and spinal cord” (PubMed Health 2013). When the myelin sheath “is damaged, nerve signals slow down or stop” thus hindering the propagation of action potentials and limiting function (PubMed Health 2013).
(Marieb, 2016). Myelin is the protective coat surrounding and insulating the nerve fibers of CNS. Myelin is fatty tissue substance that if attacked by immune cells causing a short-circuits in the current so that the successive gaps are excited more and more slowly, and eventually impulse conduction ceases which resulted in various forms of symptoms (Marieb, 2016). The degradation could either be “by inflammation, stroke, immune disorder, metabolic disorders, or nutritional deficiencies” (Slomski, 2005). The target that immune cells are sensitized to attack remains
Primarily, the term MS refers to a chronic disorder that attacks the central nervous system (CNS). It is most common in temperate continents such as Europe and Australia with Asiatic and African continents having a lower risk of the disease (Wiley Online Library, 2013). A search organised by the Multiple Sclerosis Society (2013) has estimated that there are 127,000 people living with MS in the United Kingdom. Further research by Chipps, Clanin, and Campbell (1992, pp. 158-167) shows that MS disorder more likely affects women than men with its symptoms occurring between the ages of 20 and 40 in most cases and is quite uncommon in childhood and old age. The nerve cells known as neurons in the brain constantly transmit and receive signals. They invoke emotions, activities and cognition that constitute the day to day experiences of humans. Under normal circumstances, these signals travel on a protected insulation path known as the myelin sheath. This insulation is vital as it enables signals to reach their target. In Multiple Sclerosis, the myelin sheath gets disintegrated causing the nerve fibre to be damaged leading to a disruption in the abili...
The brain is part of the central nervous system, which consists of neurons and glia. Neurons which are the excitable nerve cells of the nervous system that conduct electrical impulses, or signals, that serve as communication between the brain, sensory receptors, muscles, and spinal cord. In order to achieve rapid communication over a long distance, neurons have developed a special ability for sending electrical signals, called action potentials, along axons. The way in which the cell body of a neuron communicates with its own terminals via the axon is called conduction. In order for conduction to occur, an action potential which is an electrical signal that occurs in a neuron due to ions moving across the neuronal membrane which results in depolarization of a neuron, is to be generated near the cell body area of the axon. Wh...
When a message comes to the brain from body parts such as the hand, the brain dictates the body on how to respond such as instructing muscles in the hand to pull away from a hot stove. The nerves in one’s skin send a message of pain to the brain. In response, the brain sends a message back dictating the muscles in one’s hand to pull away from the source of pain. Sensory neurons are nerve cells that carry signals from outside of the body to the central nervous system. Neurons form nerve fibers that transmit impulses throughout the body. Neurons consists of three basic parts: the cell body, axon, and dendrites. The axon carries the nerve impulse along the cell. Sensory and motor neurons are insulated by a layer of myelin sheath, the myelin helps
Multiple sclerosis is a chronic disease of the central nervous system. It is understood as an autoimmune disease, a condition where the body’s immune system mistakenly attacks normal tissues. In Multiple Sclerosis, the patient’s own cells & antibodies attack the fatty myelin sheath that protects and insulates nerve fibres in the brain and spinal cord, the two components of the CNS. This ultimately causes damage to the nerve cells and without the insulation the myelin sheath provides, nerve communication is disrupted. Hence, Multiple Sclerosis is characterized by symptoms that reflect central nervous system involvement (Luzzio, 2014).
The neurons or brain cells are shaped like trees. Young brain cells, called soma, resemble an acorn or small seed of a tree. The seed sprouts limbs when stimulated, called dendrites. Further on in development, the cell will grow a trunk like structure called an axon. The axon has an outer shell, like the bark of a tree, called the myelin sheath. Finally, at the base of the cell, there are root-like structures called axon terminal bulbs. Through these bulbs and the dendrite of another cell, cells communicate with each other through electrochemical impulses. These impulses cause the dendrites to
The myelin sheath is a fatty substance that surrounds the axons of the nerves and provides protection. It allows messages to be sent rapidly and accurately to the axons from long distances (Serono, 2010). The axons are the part of the nervous system that allows electrical transmission of signals throughout the brain and spinal cord. Without these electrical transmissions, the body would not be able to function properly (Serono, 2010).
Creutzfeldt-Jakob Disease is an uncommon, deteriorating, consistently fatal brain disorder that is caused by prions. The symptoms of CJD are similar of Alzheimer’s but progress much faster. There are three variations of CJD, sporadic, familial, and acquired. All variations affect the brain the same way and have the same result of death. CJD is an untreatable and incurable disease.
Myelination, aka axon insulation, increases action potential conduction up to 150m/s compared to 0.5-10m/s conduction velocities of unmyelnated axons!