Re: what problems can occur whithin the muscular system?

Hello Christina

The human body contains 3 main muscular systems, and each have different 
things that can go wrong with them. The most well known muscular system and 
the one that I shall concentrate my answer to is the skeletal muscle 
system.  However there is also smooth muscle that makes up a large portion 
of the walls of the stomach, intestines, bladder, arteries, and many other 
parts of the body.  Then there is cardiac muscle, which is a unique muscle 
type specific to the heart.  The skeletal muscle system is sometimes 
referred to as voluntary muscle because we can control what it does.  This 
enables us to move around and perform tasks in our every day lives.

Diseases of voluntary muscle are called myopathies.  Either these are 
caused by a external influences such as disease and infection or by genetic 
defects which occur when there is a problem with one of the genes that are 
responsible for the way the body is made up.  

Inflammatory myopathies are when the muscle becomes swollen which can be 
very painful and make the muscle weak. These are generally caused by 
bacterial, viral or parasitic infections that affect the muscle.

Metabolic and endocrine myopathies are caused by the bodies own hormones 
and systems when they are not working properly.  An example of this is 
thyroid disease.  The thyroid is a gland in the neck that produces 
hormones, which control the metabolic rate of many tissues, and over 
activity or under activity of the gland can pose many problems with the 
muscular system.

Another cause of problems is at a place called the neuromuscular junction. 
 This is where the nerves from the brain meet the muscle and the signal for 
a muscle to contract has to be passed from one to the other.  This is done 
with substances called neurotransmitters, which are chemicals that are 
passed from the nerve to the muscle to transmit the signal.  If there is a 
problem with either the production of the chemical by the nerve or the 
detection of the chemical by the muscle then this will lead to problems 
controlling the movement of the muscles.  An example of such a disease is 
"Myasthenia Gravis" where up to 90% of the receptors for the 
neurotransmitter acetlycholine have been damaged by the bodies immune 
system.  This causes the muscles to feel tired much more quickly than they 
would normally.

Possibly the most well known problems with the muscular system is muscular 
dystrophy.  This is a genetic disease.  Most muscular dystrophies are 
caused my mutations in one particular gene that means this diseases mainly 
affects males because of the way it is transmitted.  (It is an X-linked 
recessive disorder).  This gene is responsible for the production of a 
protein in the muscle called dystrophin, which is in turn responsible for 
how the muscle structure is assembled.  Problems with this protein mean 
that the cells to do assemble correctly and so the muscle does not work 
properly.  There are other muscular dystrophies that are caused by defects 
in other genes.

Channelopathies.  These are rare disorders caused by defects in ion 
channels in the muscle.  Many systems in the body are controlled at the 
level of the cell by the movement of small ions across the cell membrane.  
Ions involved in this include calcium, potassium and chloride ions  and the 
movement of these ions is controlled by ion channels that can open and 
close depending on whether or not they want the ion to get through.  If 
there is a problem with these ion channels, it can affect the way that the 
muscle contraction is controlled and the muscles do things that we don't 
want them to.

E.g. Myotonias are characterised by a continued contraction of the muscle 
after the voluntary effort has stopped.  This is caused by a genetic defect 
in the chloride ion channel.

Another ion that causes problems in muscle is potassium.  Problems with the 
body that cause high or low levels of potassium in the blood can cause 
muscle weakness because this interferes with how the muscles are regulated.

This is a very brief insight into the sorts of problems that are found in 
the muscular system.

Much more detail can be found at  http://www.bio.uni
pd.it/~telethon/MuscleNET.html.

Regards