Many snake venoms, including those from the rattlesnake, interfere with blood clotting in some way. Destruction or alteration of components of the clotting process, for example the protein fibrinogen, is a common method, with the result that clotting does not occur. At the same time enzymes are degrading tissue and muscle. The muscle is degraded by the action of a specific toxin, myotoxin, which increases the calcium level in muscle, precipitating the self-destruction of the muscle tissue. Destruction of blood cells also occurs, again through the action of enzymes, and there may also be coagulation of small blood cells. The victim may die within an hour, but the average is between 18 and 32 hours. This is usually due to a loss of blood pressure or shock from the loss of fluid in the circulatory system and blood cells.
With cobra venom, the major effect is due to a toxin that acts on the nervous system. This neurotoxin is a small molecule, which can distribute throughout the body rapidly. It acts like curare, paralysing the centre in the brain that controls breathing. By acting at the point where nerves control muscles it blocks the transmission of nerve impulses and causes muscle weakness and again affects breathing. The eyelids droop and speech becomes incoordinated.
In addition, cobra venom contains a toxin that causes changes in the heart rhythm and a loss of blood pressure. Finally, a further toxin and a combination of enzymes cause red blood cells to rupture. Thus a bite from the cobra will be rapidly fatal.
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