Paralysis (also known as plegia) is a loss of motor function in one or more muscles. Paralysis can also be accompanied by a loss of feeling (sensory loss) in the affected area if there is sensory damage. In the United States, roughly 1 in 50 people have been diagnosed with some form of permanent or transient paralysis. The word "paralysis" derives from the Greek παράλυσις, meaning "disabling of the nerves" from παρά (para) meaning "beside, by" and λύσις (lysis) meaning "making loose". A paralysis accompanied by involuntary tremors is usually called "palsy". Causes
Paralysis is most often caused by damage in the nervous system, especially the spinal cord. Other major causes are stroke, trauma with nerve injury, poliomyelitis, cerebral palsy, peripheral neuropathy, Parkinsons disease, ALS, botulism, spina bifida, multiple sclerosis, and Guillain–Barré syndrome. Temporary paralysis occurs during REM sleep, and dysregulation of this system can lead to episodes of waking paralysis. Drugs that interfere with nerve function, such as curare, can also cause paralysis. Pseudoparalysis (pseudo- meaning "false, not genuine", from Greek ψεῦδος) is voluntary restriction or inhibition of motion because of pain, incoordination, orgasm, or other cause, and is not due to actual muscular paralysis. In an infant, it may be a symptom of congenital syphilis. Pseudoparalysis can be caused by extreme mental stresses, and is a common feature of mental disorders such as panic anxiety disorder. Variations
Paralysis can occur in localised or generalised forms, or it may follow a certain pattern.
Most paralyses caused by nervous-system damage (e.g., spinal cord injuries) are constant in nature; however, some forms of periodic paralysis, including sleep paralysis, are caused by other factors.Paralysis can occur in newborns due to a congenital defect known as spina bifida. Spina bifida causes one or more of the vertebrae to fail to form vertebral arches within the infant, which allows the spinal cord to protrude from the rest of the spine. In extreme cases, this can cause spinal cord function inferior to the missing vertebral arches to cease. This cessation of spinal cord function can result in paralysis of lower extremities. Documented cases of paralysis of the anal sphincter in newborns have been observed when spina bifida has gone untreated. While life-threatening, many cases of spina bifida can be corrected surgically if operated on within 72 hours of birth. Ascending paralysis presents in the lower limbs before the upper limbs. It can be associated with:

Guillain–Barré syndrome (another name for this condition is Landrys ascending paralysis)
Tick paralysisAscending paralysis contrasts with descending paralysis, which occurs in conditions such as botulism. Other animals
Many animal species use paralyzing toxins to capture prey, evade predation, or both. In stimulated muscles, the decrease in frequency of the miniature potentials runs parallel to the decrease in postsynaptic potential, and to the decrease in muscle contraction. In invertebrates, this clearly indicates that, e.g., Microbracon (wasp genus) venom causes paralysis of the neuromuscular system by acting at a presynaptic site. Philanthus venom inhibits both the fast and slow neuromuscular system at identical concentrations.