PARALYSIS or PALSY, a medical term usually implying the loss or impairment of voluntary muscular power. Paralysis is rather a symptom than a disease per se; it may arise (I) from injury or disease of nervous and muscular structures (organic paralysis), or (2) from purely dynamic disturbances in the nervous structures of the brain which preside over voluntary movement. The latter is functional motor paralysis, a symptom common in certain neuroses, especially hysteria. For general paralysis of the insane, see INSANITY.
Whether the loss of motor power be functional or organic, it may be generalized in all the muscles of the body, or localized to one or many. The different forms of paralysis which may arise from organic disease can be understood by a consideration of the motor path of voluntary impulses from brain to muscle. There are two neural segments in this path, an upper cerebral and a lower spinal; the former has its departure platform in the brain and its terminus in the whole of the anterior grey matter of the spinal cord, whence issues the lower spinal segment of the motor path to the muscles. The nerve fibres of the upper cerebral segment are prolongations of the large psycho-motor cells ; the nerve fibres of the lower segment are prolongations by the anterior roots and motor nerves of the large cells in the grey matter of the cord. Disease or destruction of any part of the upper cerebral segment will give rise to loss of voluntary power, for the in fluence of the mind on the muscles is removed in proportion to the destruction of this efferent path. Disease or destruction of the lower spinal segment causes not only loss of voluntary power but an atrophy of the muscles themselves.
Paralysis may therefore be divided into three great groups: (I) loss of voluntary power without muscular wasting except from disuse, and without electrical changes in the muscles due to injury or disease in the upper cerebral segment ; loss of muscular power with wasting and electrical changes in the muscles due to disease or injury in some part of the lower spinal segment ; (3) primary wasting of the muscles.
The more common forms of paralysis will now be described. Hemiplegia, or paralysis affecting one side of the body, is a frequent result of apoplexy (q.v.) ; there is loss of motion of the tongue, face, trunk and extremities on the side of the body opposite the lesion in the brain. In complete hemiplegia both arm and leg are powerless; the face is paralysed chiefly in the lower part, while the upper part moves almost as well as on the un paralysed side, and the eye can be shut at will, unlike peripheral facial paralysis (Bell's palsy). The tongue when protruded de viates towards the paralysed side, and the muscles of mastication contract equally in ordinary action, although difficulty arises in eating, from food accumulating between the cheek and gums on the paralysed side. Speech is thick and indistinct, and when there is right-sided hemiplegia in a right-handed person, there may be associated various forms of aphasia (q.v.), because the speech centres are in the left hemisphere of the brain. Some muscles are completely paralysed, others are merely weakened, while others, e.g., the trunk muscles, are apparently unaffected. In many cases of even complete hemiplegia, improvement, especially in children, takes place after a few weeks or months, and is generally first indicated by return of movement in the muscles which are habitually associated in their action with those of the opposite unparalysed side ; thus, movement of the leg returns first at the hip and knee joints, and of the arm at the shoulder and elbow, although the hand may remain motionless. The recovery, however, in the majority of cases is only partial, and the sufferer is left with a permanent weakness of one side of the body, often associated with contracture and rigidity, giving rise to a characteristic gait and attitude.