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There are several possible causes of paralysis, and the major ones are :
- Poliomyelitis (polio)
- Amyotrophic lateral sclerosis
- Spina bifida
- Multiple sclerosis
- Guillain-Barré syndrome
Paralysis is most often caused by damage to the nervous system or brain, especially the spinal cord while the muscles themselves stay intact. Beside the motoric symptoms of paralysis, there are also often some sensorial symptoms such as a loss of feeling in the affected area. 
Hysteria or severe emotional trauma may also cause paralysis. 
The most common type of temporary paralysis is when muscles do not get the blood flow they need such as when sitting or sleeping with an arm or leg in a position that restricts the blood flow; in layman's terms when your arm(s) or leg(s) fall asleep.
Some Characteristics of Paralysis
Paralysis may be divided into three big groups:
- Localized - This is a very common form of paralysis which is usually caused by a stroke. Patients often have hemiplegia (weakness on one side of the body) or other patterns of paralysis depending on the area of damage in the brain by a stroke. 
- Generalized - This is a common form of paralysis in which patients with stroke may be weak throughout their body. It is also called global paralysis. 
- Paralysis that follows a particular pattern. 
Common Causes of Paralysis
There are many possible causes of paralysis, and the most common causes of paralysis are:
A stroke or a brain attack represents an acute neurological injury in which the blood supply to a part of the brain is interrupted by several possible factors. 
The part of the brain which was left with disturbed perfusion can no longer receive adequate oxygen carried by the blood, which leads to the death of brain cells, impairing the function of that part of the brain. Risk factors for stroke include :
- Diabetes mellitus
- High cholesterol
- Cigarette smoking
Poliomyelitis is a viral paralytic disease caused by a virus called the polio virus. This virus enters the body orally, infecting the intestinal wall. It may also enter the bloodstream and get into the central nervous system, causing muscle weakness and often paralysis.Young children who contract polio may sometimes suffer only mild symptoms which can make it hard to diagnose the condition. People who have survived polio sometimes develop additional symptoms, notably muscle weakness and extreme fatigue, decades after the primary infection. These symptoms are called post-polio syndrome. 
Amyotrophic Lateral Sclerosis
Amyotrophic Lateral Sclerosis is a very progressive and almost invariably fatal neurological disease. Experts have discovered that, in Amyotrophic Lateral Sclerosis, both the upper motor neurons and the lower motor neurons are affected and they degenerate and eventually die. When this happens, muscles are unable to function, and they gradually weaken and waste away. More than 30,000 Americans have this disorder, and an estimated 5,000 cases of the disease are diagnosed in the United States per year. 
Botulism represents a rare but serious paralytic disease caused by a nerve toxin called botulin, which is a poison produced by the bacterium Clostridium Botulinum. It is a very dangerous and potent toxin which is capable of blocking nerve function and causing respiratory and musculoskeletal paralysis. 
There are three main kinds of botulism :
- Food-borne botulism - caused by eating foods that contain the botulism toxin.
- Wound botulism - caused by toxin produced from a wound infected with Clostridium Botulinum
- Infant botulism - caused by consuming the spores of the bacteria, which then grow in the intestines and release the toxin.
Spina bifida is a term which means split or divided spine. It represents a birth defect caused by an incomplete closure of one or more vertebral parts of the spine, resulting in malformations of the spinal cord which fall into three categories :
- Spina bifida occulta
- Spina bifida cystica
Multiple sclerosis is a chronic, inflammatory disease that affects the central nervous system. Multiple sclerosis affects neurons and their cover called myelin, causing various symptoms depending upon which signals are interrupted .
Guillain-Barré syndrome is a rare immune-mediated inflammatory disorder of the nervous system. The pathologic mechanism of the disease is a loss of myelin in peripheral nerves due to an acute inflammation. The cause of this inflammation is unknown. Scientists believe that Guillain-Barré syndrome is an autoimmune disease, meaning that the sufferer's immune system is triggered into damaging the nerve covering. 
Trauma to the Spinal Cord
When a person suffers a spinal cord injury, the spinal nerves joining the cord below the level of an injury will be either completely or partially cut off from the brain. This damage can result in Quadriplegia (paralysis that usually affects the cervical spinal nerves resulting in paralysis of all four limbs) or Paraplegia, complete paralysis of the legs and abdomen up to the nipple line. Nerves joining the spinal cord above the level of injury will be unaffected and continue to work as in a person who didn't suffer a spinal cord injury. 
Periodic or Temporary Paralysis
There is also one specific type of paralysis called periodic paralysis. A periodic paralysis is a group of rare genetic diseases that lead to weakness or paralysis from common triggers such as cold, heat, high carbohydrate meals, hunger, stress or excitement and physical activity. The underlying mechanism of these diseases are malfunctions in the ion channels in skeletal muscle cell membranes that allow electrically charged ions to leak in or out of the muscle cell, causing the cell to depolarize and become unable to move.