How do cardiac and smooth muscles differ from skeletal?
1 Answer
These three types of muscles have different characterics and different jobs.
Skeletal muscles are found in pairs and move bones. They have striations which can be seen under the microscope. Because of this they are often called striated muscle.
They are also called voluntary muscles because we have to think to make them move.
Smooth muscles appear smooth under a microscope and are called involuntary as we do not have to think to make them move.
They also contract very slowly and in waves (peristalsis). They are found in all hollow organs except the heart.
Cardiac (heart) muscle are only found in the heart. They are striated like skeletal muscle but they are also involuntary.
The heart muscle is rather odd. If you would take just a few cells and place them in a Petri dish and spread them apart, each one will beat on it's own. If you would push them together, the beating would stop for a millisecond and then they would all beat as one.
The heart does have nervous innervation through the autonomic system (as does smooth muscle) but it doesn't need it.
It has pacemaker cells that regulate the beat. These cells are not nervous tissue but specialized cardiac cells. These are the SA (sinus) node and the AV node.
