Nerve_Cell========<::::|:::|      \
                             /   |:::|       - Muscle cell
                Transmitter      |:::|      /


Skeletal muscle takes orders from nerves. Nerve cells give those orders to muscle with chemicals  called "transmitters" - neurotransmitters. The super duper transmitter for muscle is a chemical called acetylcholine . Don't worry about what it looks like. It's just a key that fits a protein lock. That chemical released from the nerve fits into a protein on the muscle surface (which is fairly intimate with  the nerve ending). Once that key is in the lock a cascade of "signal" or wave of signal spreads over the muscle as sodium and potassium get swapped in & out of the cell as if a wave at a football game.

 If acetylcholine were missing or if the protein lock (receptor) were amiss, the effect would be no transmission of signal from nerve to muscle.

 In myasthenia, there are insufficient ACTIVE receptor proteins (working ones, at least). The body damages its own acetyl choline receptors by way of auto immune disease. That is, antibodies are  mistakenly made against the receptor proteins and latch on in such a way that acetylcholine cannot get in to activate the mechanism. PERHAPS the antibodies are made against something else that has a  portion that looks so much like the receptor proteins that the antibody can't distinguish them. There are several, otherwise unrelated, well known post infection diseases wherein the immune response to  bacteria winds up leaving antibodies around that attack self, one's own substance, causing heart or kidney disease etc. What actually causes it in MG is not too clear, yet.

 In this case the foreign entity may well be called "mother" as many babies with myasthenia are born of myasthenic mothers. The antibody from the mother may damage fetal chemical receptors. It can be  paralyzing enough to cause the motion sensing cellular processes of joint development to fail (resulting in failure to make or to completely make joints - which require movement of muscle to go to completion - a syndrome called arthrogryposis results - although there are other motion messing causes possible as well). Lupis - a disease of immunity run amok - also can produce this along with other  tissue type damage as lupis often targets many proteins.

Babies with myasthenia have a habit of being born prematurely. It is easy to blame prematurity for many things when we need to remember that many things result in prematurity.

In congenital form, although the target of myasthenia is as broad as all skeletal muscle, certain locations show up most prominently. Early on eyes are most involved. There is both inability to open  the lids and the eyes do not converge on anything (eye muscles are not working). The cry is weak sounding and nursing is weak.

 The hereditary forms (familial or familial infantile) is often even nastier at first as babies are born blue and need to be artificially assisted in breathing. The eyes are not the most prominent weakness as the  involvement is prominent over the whole of the body. If there is no secondary damage, the tendency is to improve with age although relapses do occur along the way.

 There are other variants, but these are the main ones. The mainstay of treatment of the neurotransmission defect is drug based. Orthopedics gets involved for the secondary deformities and postural disturbances.

Removal of the Thymus (which produces the problem substance) is helpful in many cases.

Biologics: We are on the brink of being able to make substances which will take out trouble making proteins. Even though the biggest target disease is rheumatic arthritis, the basic science is so close that whatever works for that will spill over to many other disorders.

The section on Botulinum toxin has a more detailed description of the acetylcholine transmission (though in another context).