also called palsy loss or impairment of voluntary muscular power. For paralysis from psychiatric causes, see hysteria. Most of the commonly encountered diseases that produce paralysis can be divided into two main groups depending on whether they entail structural alterations in nervous or muscular tissue, or lead to metabolic disturbances in neuromuscular function. Some act in a systematic way and affect one of the three elements in the motor system (upper and lower neuron and muscle) more or less extensively and exclusively. More often, however, one element or neighbouring portions of two of the three elements are involved over a limited extent by a single focal lesion. The most common cause of hemiplegia (paralysis of the muscles of the lower face, arm, and leg on the side opposite the main lesion) is damage to the corticospinal (pyramidal) tracts and associated motor tracts in one hemisphere of the brain from obstruction (blood clot, or thrombosis) or rupture (cerebral hemorrhage) of a major cerebral artery. Brain tumour is another but less common cause of hemiplegia and develops and increases in severity gradually over a period of weeks or months. When the lesion is in the left hemisphere in a right-handed person, the resulting right hemiplegia is often associated with one of the various forms of aphasia, such as inability to sound words, to write, or to read. Bilateral hemiplegia with pseudobulbar palsy results from diffuse, bilateral brain disease such as occurs in severe cerebral arteriosclerosis or cerebral vascular syphilis. The terms cerebral palsy and spastic diplegia refer to bilateral hemiplegia resulting from prenatal developmental brain defects or from injury to the brain at birth. The spinal cord is rarely the site of vascular obstruction or hemorrhage. The more common causes of damage to the pyramidal tracts in the cord include deformities of the spinal column from bone and joint disease and from injury to the spine with fracture and dislocation, spinal cord tumours, and a number of inflammatory and degenerative diseases and changes associated with pernicious anemia. One of the most common causes of progressive spastic paraplegia in persons past middle age is spinal degenerative arthritis, with protrusion of an intervertebral disk cartilage into the lower cervical portion of the spinal canal. Of the diseases that attack lower motor neurons and result in flaccid paralysis with muscular wasting, the most common are poliomyelitis and polyneuritis, the former affecting the cell bodies of bulbar and spinal motor neurons and the latter affecting their peripheral processes. Bell's palsy is a peripheral neuritis of unknown cause affecting a single nerve trunkthe facial nerveand resulting in paralysis of all the muscles of one side of the face. In the majority of cases, recovery eventually occurs. Diseases that result in paralysis through primary changes in muscle tissue are fewer than the above. Of the conditions belonging in this category, progressive muscular dystrophy is the only one apparently confined to the muscles. This is a familial, hereditary disease characterized by progressive, symmetrical muscular weakness and wasting. One rare variety has its onset before puberty, is more common in boys, and usually progresses to severe disability within a few years. It is known as pseudohypertrophic muscular dystrophy. The other types of dystrophy, in general, begin in adolescence or young adult life, and the two sexes are about equally affected. The progress of these other forms is slow; and life expectancy is not necessarily shortened, nor is severe disability inevitable. Muscular weakness without structural alteration in nerve or muscle tissue may be a symptom of disturbances in metabolism arising from a wide variety of causes. Among such conditions are diseases of the endocrine glands, certain intoxications, and several metabolic defects. The most common example of a metabolic disorder in neuromuscular function of unknown cause is myasthenia gravis. In this condition there is muscular weakness, without atrophy, which may be mild or severe and either generalized or restricted to a few muscle groups. Some of the muscles innervated by cranial nerves are affected in almost every case. The weakness of myasthenia gravis results from a localized defect in the chemical processes involved in the transmission of impulses from motor nerve endings to muscle fibres. Although the cause of this defect and its precise nature are unknown, several drugs facilitate the transmission of impulses from nerve to muscle. One of these, neostigmine, has proved to benefit most patients but does not correct the basic, unknown defect.
Meaning of PARALYSIS in English
Britannica English vocabulary. Английский словарь Британика. 2012