Paralysis (pl.:paralyses; also known asplegia) is a loss ofmotor function in one or moremuscles. Paralysis can also be accompanied by a loss of feeling (sensory loss) in the affected area if there is sensory damage. In theUnited States, roughly 1 in 50 people have been diagnosed with some form of permanent or transient paralysis.[1] The word "paralysis" derives from theGreek παράλυσις, meaning "disabling of the nerves"[2] from παρά (para) meaning "beside, by"[3] and λύσις (lysis) meaning "making loose".[4] A paralysis accompanied by involuntary tremors is usually called "palsy".[5][6]
Pseudoparalysis (pseudo- meaning "false, not genuine", from Greek ψεῦδος[7]) is voluntary restriction or inhibition of motion because of pain, incoordination, orgasm, or other cause, and is not due to actual muscular paralysis.[8] In an infant, it may be a symptom ofcongenital syphilis.[9] Pseudoparalysis can be caused by extreme mental stress and is a common feature of mental disorders such aspanic anxiety disorder.[10]
Paralysis can occur in localized or generalized 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 ofperiodic paralysis, includingsleep paralysis, are caused by other factors.[11][12]
Paralysis can occur in newborns due to a congenital defect known asspina 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.[12] 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.[11] 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:
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. It causes a decrease in the frequency of the miniature potentials without affecting their amplitude significantly.[citation needed]
In some species ofwasp, to complete the reproductive cycle, the female wasp paralyzes a prey item such as a grasshopper and places it in her nest. In the speciesPhilanthus gibbosus, the paralyzed insect (most often a bee species) is coated in a thick layer of pollen. The adultP. gibbosus then lays eggs in the paralyzed insect, which is devoured by thelarvae when they hatch.[14]
A renowned example of a vertebrate-produced paralyzing toxin is thetetrodotoxin of fish species such asTakifugu rubripes, the famously lethalpufferfish of Japanesefugu, which works by binding tosodium channels in nerve cells, inhibiting the cells' proper function. A nonlethal dose of this toxin results in temporary paralysis. This toxin is also present in many other species ranging from toads tonemerteans.
Paralysis can be seen in breeds of dogs that arechondrodysplastic. These dogs have short legs, and may also have short muzzles. Their intervertebral disc material can calcify and become more brittle. In such cases, the disc may rupture, with disc material ending up in the spinal canal, or rupturing more laterally to press on spinal nerves. A minor rupture may only result inparesis, but a major rupture can cause enough damage to cut off circulation. If no signs of pain can be elicited, surgery should be performed within 24 hours of the incident, to remove the disc material and relieve pressure on thespinal cord. After 24 hours, the chance of recovery declines rapidly, since with continued pressure, the spinal cord tissue deteriorates and dies.
Another type of paralysis is caused by a fibrocartilaginous embolism. This is a microscopic piece of disc material that breaks off and becomes lodged in a spinal artery. Nerves served by the artery will die when deprived of blood.
TheGerman Shepherd Dog is especially prone to developing degenerativemyelopathy. This is a deterioration of nerves in the spinal cord, starting in the posterior part of the cord. Affected dogs will become incontinent and gradually weaker in the hind legs as nerves die off. Eventually, their hind legs become useless. This disease also affects other large breeds of dogs.
Cats with aheart murmur may develop blood clots that travel through arteries. If a clot is large enough to block one or both femoral arteries, there may be hind leg paralysis because the major source of blood flow to the hind leg is blocked.
Many snakes and trees exhibit powerfulneurotoxins that can cause nonpermanent paralysis or death.
