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Roguewolfe t1_jdegqw0 wrote

Reply to comment by TackingIntoTheWind in TIL that the Hemlock Water Dropwort is the most poisonous plant in the UK. Its poison constricts the muscles, causing death by asphyxia, which also causes a rictus like death grin. Use of this plant in Phoenician Sardinia for executions is the origin of the term "Sardonic Grin". by AspireAgain

It's exactly like that. Quite a few nasty things can cause that type of spastic paralysis (defined as paralysis where muscles cannot relax or un-flex: it's the opposite of flaccid paralysis where they cannot flex).

Your brain, nerves, and muscles have an interconnected system bridged by a small physical gap called the neuromuscular junction. This tiny gap has neurotransmitters that flow between a motor neuron and a muscle. First, your brain decides you want to move or make a motion of some sort, and communicates that to the cerebellum, which subconsciously coordinates the movement (because all movements are quite a bit more complicated and involve more muscles than we realize consciously). Next, the cerebellum, via the spinal cord, sends a message to the muscles saying, "flex!" That message is communicated via a small messenger molecule, acetylcholine. When we no longer wish to flex, we both stop emitting acetylcholine and we actively destroy and recycle any acetylcholine remaining in the junction using enzymes (acetylcholinesterase iirc).

Things that cause paralysis (other than brain and spinal cord injuries) interrupt this process in some way. Things that cause spastic paralysis either mimic acetylcholine but don't get destroyed by enzymes so they stick around for a long time, or they do it by preventing enzymes from finding and reacting with acetylcholine. In the latter example, they usually bind to the enzymes themselves, and "plug it up". In the former example, they bind to the acetylcholine receptor on the muscle cell, activating it and also "plugging it up" such that it stays turned on regardless of what our brain is trying to tell it.

You could also cause flaccid paralysis by disrupting the release of acetylcholine, or by plugging up the muscle receptor with a molecule that binds to it but does not activate it, similar to but critically different from the spastic example in how it affects the cell's interior.

There's quite a lot of plant and insect toxins that can do one or the other. Curare is an often used example in undergraduate biology.

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Crepuscular_Animal t1_jdfmlz9 wrote

Thank you! I always love it when there's a well-researched comment under a post to learn something new. I've looked up curare and found this neat:

Curare is deadly but it can be used as an antidote to another dangerous poison, strychnine, because their acetylcholine activity cancels each other.

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bestp0282 t1_jdg0glf wrote

It’s best known use though is as a medical grade paralytic. Rocuronium, vecuronium, and other derivatives (notice the root of the word “cur” as in curare) are used every day to keep people relaxed during surgery

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Crepuscular_Animal t1_jdg2bya wrote

Cool! I also dig the fact that botulotoxin, one of the deadliest substances to exist naturally, is successfully used in medicine. Botox treatment doesn't only remove wrinkles from skin, it can deal with spasms, tics, chronic pain, excessive sweating... basically everything that can be stopped by suppressing nerve signals. Who knew that swollen tins of biohazardously spoiled food contain the key to curing so many conditions.

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Ladranix t1_jdg57cn wrote

Tetanus fun fact! It functions as a precision set of molecular "scissors" and cleaves the synaptobrevin2/VAMP protein complex SNARE in inhibitory interneurons. The SNARE complex is responsible for the exocytosis of neurotransmitters, and the inhibitor neurons basically send the "off" signal to the rests of your neurons and tells them to stop firing. The degradation of the synaptobrevin protein prevents these signals from being sent causing massive overreactions in muscles to any and all stimuli. The really cool part is because the toxin is so specifically targeted to this specific type of cell, parts of it are being co-opted to deliver medications in a targeted fashion!

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