Paralysis is the complete loss of muscle function for one or more muscle groups. Paralysis can cause loss of feeling or loss of mobility in the affected area.
Paralysis could be localized, or generalized, or it may follow a certain
pattern. Most paralyses caused by nervous system damage (i.e. spinal
cord injuries) are constant in nature; however, there are forms of
periodic paralysis, including sleep paralysis, which are caused by other
Many animal species use paralyzing toxins to capture prey,
evade predation, or both. A well-known example is the tetrodotoxin of
fish species such as ''Takifugu rubripes'', the famously lethal
pufferfish of Japanese fugu. This toxin works by binding to sodium
channels in nerve cells, preventing the cells' proper function. A
non-lethal dose of this toxin results in temporary paralysis. This toxin
is also present in many other species ranging from toads to nemerteans.
Another interesting use of paralysis in the natural world is
the behavior of some species of wasp. To complete the reproductive
cycle, the female wasp paralyzes a prey item such as a grasshopper and
places it in her nest. She then lays eggs in the paralyzed insect, which
is devoured by the larvae when they hatch. Many snakes also exhibit
powerful neurotoxins that can cause non-permanent paralysis or death.
Paralysis can be seen in breeds of dogs that are
chondrodysplastic. 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 in paresis, but a major rupture
can cause enough damage to cut off your 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 the spinal
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.
The German Shepherd is especially prone to developing
degenerative myelopathy. This is a deterioration of nerves in the spinal
cord, starting in the posterior part of the cord. Dogs so affected will
become gradually weaker in the hind legs as nerves die off. Eventually
their hind legs become useless. They often also exhibit fecal and
urinary incontinence. As the disease progresses, the paresis and
paralysis gradually move forward. This disease also affects other large
breeds of dogs. It is suspected to be an autoimmune problem.
Cats with a heart 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.
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