Snake venom is made up of nerve toxins which can block or over-stimulate the nervous system and kill.
When the nerve toxins are injected into the blood, they cause paralysis of muscles required for breathing.
Depending on the snake, paralysis may be very rapid or take up to ten hours.
The Black Mamba’s venom is primarily composed of potent neurotoxins that may cause a fast onset of muscle paralysis
Snake venoms start their paralysing effects on the muscles around the eyes (typically manifest as fixed dilated pupils, reduced eye movements and droopy eyelids).
If not treated with antivenom, these early signs will eventually be followed by increasing difficulty talking, swallowing and, ultimately, breathing.
Another potentially lethal effect of snakebite, rarely seen with other types of venoms, is altered blood clotting.
Most of Australia’s dangerous snakes have toxins in their venom that cause the body to destroy factors that help clot blood.
A more insidious effect is muscle destruction known as myotoxicity.
While not as quick as the effect on blood clotting, heart function or nerve signalling, myotoxicity can also be lethal.
Typically, snake venom toxins dissolve the membrane of muscle cells.
Not only is this a painful experience, it also causes the muscle protein, known as myoglobin, to leak into the urine, potentially poisoning the kidneys in the process.
Myotoxicity can also lead to massive increases in blood potassium levels, leached from the injured muscle cells.
This effect can itself cause fatal damage to the normal rhythm of the heart.
Although many venoms have evolved to rapidly paralyse and digest prey, another important venom action is defence.
Aside from the physical trauma to the skin from a bite or a sting, these venoms frequently contain toxins that act in various ways to injure cells, trigger inflammation and even kill skin cells.
All of this can cause severe pain.
Source: The Conversation