How do muscle relaxants work and why are there so many types?

[misskitty]

How do muscle relaxants work and who discovered how they work? Why are there so many different kinds of muscle relaxants? Are there any that are natural?

 

[Huckleberry]

Muscle relaxants affect the central nervous system. I imagine that there are so many of them because they are each a different chemical compound and may have different effects. From a business point of view each drug has a patent and another pharmaceutical company would need to sell a different drug. I don't know who discovered muscle relaxants but they can be found in nature and have been used by humans probably for millenia. I believe some of those brightly colored frogs in South America have an extremely powerful muscle relaxant that coats their skin. It is so powerful that just a few nanoliters absorbed through skin contact can stop a persons heart. Indiginous tribes use the frogs to coat their poison darts. Some of the muscle relaxants used in prescription drugs today may have been made by analyzing the organic chemicals from plants and animals such as these frogs and creating a synthetic version of the same thing but with a lower molar concentration.

 

[bor0000]

yes, in our cell metabolism class we discussed a little on this. the topic where you get an introduction to this subject is: 'metabotropic ion channels'-in summary-a motor neuron releases chemicals which bind an ion channel(acetylcholine nicotinic receptor) on a muscle fiber. this causes a conformational change in the ion channel and it opens, leading to a pathway which makes the muscle contract. after the chemical is removed from the receptor, the ion channel closes... some drugs/poisons may inhibit the removal of the chemical from the receptor, by blocking enzymes such as cholinestarase or by some other mechanisms. in various cells there are various receptors(i.e. heart muscle cells i think have beta-adrenergic receptors, to which the binding of norephinephrine stimulates contraction and muscarinic-acetylcholine receptors to which the binding of acetylcholine stimulates relaxation), so various drugs may affect various receptors.. also the drugs, or even bacteria, can affect the central nervous system, so that the neurons don't even reach the cells(they do it the same way, by increasing or decreasing the amount of chemicals that can be released from 1 neuronal cell to the next one in sequence).

chapter 7 in Loedish textbook gives introduction to the ion channels
and chapter 13 on the G-proteins and gives some introduction to the 'intercellular and intracelluar cell signalling' and discusses various pathways. for example some drugs can inhibit something much further in the pathway. such as the neuron can cause the nicotinic receptor to open/close normally, and it activates a protein which then causes a sequence of enzymes to open a voltage-gated Calcium channel and cause the muscle to contract. but some drug can make it so that calcium is then not removed from the cell cytosol and then the muscle cell will be desensitized,etc.

oh and in that same chapter 13 they give a small picture which shows that cell signalling can be affected in many different ways throughout the pathway.

 

[Moonbear]

I feel so unneeded around here.

The folks here are doing a great job explaining things to each other.

I'll just reinforce that the reason for having so many different types of muscle relaxer is that they have different mechanisms of action. As bor0000 has described, there are many steps involved in the signal for muscles to contract, so different compounds can target different parts of those pathways.

 

[bor0000]

some of the things i wrote i got mixed up. i did that as a review of some lectures, as i have finals coming up. so i think the most useful thing from my message is as the next poster outlined 'there are many mechanisms', and also that you can read a textbook(i gave the chapters).

 

[misskitty]

Ok, that's great info. Moonbear we all love you!

So are there any other natural muscle relaxants other than the skin of the poision dart frogs?

 

[Huckleberry]

Yes, there are many types.
http://library.thinkquest.org/C007974/4cla.htm
http://members.aol.com/Bio50/LecNotes/lecnot12b.html

alpha-neurotoxins Postsynaptic neurotoxins that block the acetylcholine receptor (neuromuscular) Elapid venoms only in snakes, also found in spiders and cone snails

Tetrodotoxin-like acute respiratory failure through paralysis of the respiratory musculature with death as a result Blue-ringed octopi, poison dart frogs, pufferfish

The poison found in pufferfish, blowfish, balloon fish, toads, sunfish, porcupine fish, toadfish, globefish, and swellfish is a tetrodotoxin. This is one of the most toxic poisons found in nature. Most people who eat pufferfish do so intentionally; pufferfish are considered an Asian delicacy, served in some types of sushi and sashimi. Unless the chef is specially trained to cut the meat in a particular fashion, the dish may contain a large amount of the toxin. Pufferfish poisoning is similar to paralytic shellfish poisoning.

And the poison from dart frogs and the blue-ring octopi can be absorbed through your skin. I checked on plant neuromuscular inhibitors too

There are 2 basic types of ACh receptors:
Muscarinic type:
Stimulated by the mushroom poison, muscarine
Found in parasympathetic synapses on organs like the heart and intestines; also found in the central nervous system
Nicotinic type:
Stimulated by the plant toxin, nicotine
Found in neuromuscular junctions and autonomic ganglia
Natural ACh receptor inhibitors include:
Curare: South American arrow poison produced from the vine, Chondodendron tomentosum
Atropine: from several plants, including Jimson weed (Datura stramonium), thornapple and nightshade (Belladonna atropa)
Scopolamine: from the henbane plant (Hyoscyamus niger)
Atropine and scopolamine inhibit muscarinic receptors; the other toxins inhibit nicotinic types

Hope you read this.

 

[misskitty]

Yes Huck I read it. That was a good post. Thanks.