What Are the Structural and Functional Differences Between Skeletal, Smooth and Cardiac Muscles and Where Are They Found?

Skeletal muscle is the type normally thought of when one thinks of the word muscle, but do not be mislead, this is only one of three different types of muscle. The three different muscles, classified by their general microscopic appearance, are skeletal, cardiac and smooth. Let's start first with skeletal.

Skeletal muscle is characterized by elongated, multi-nucleated fibers, or cells, with striations due to light, I band, and dark, A band, alternations. The nuclei of the fibers are not centered, but rather located towards the outer edge of the cells. These muscles are under somatic or voluntary control. This means they are under immediate conscious control by the nervous system. Skeletal muscle has a name related to its function since it is usually associated with attachment to and movement of bones and cartilage. Skeletal muscle requires either extrinsic nerve or hormonal stimulation to create action potentials, which trigger movement.

Cardiac, like skeletal muscle, is also striated. Though unlike skeletal, cardiac muscle cells are short and branched with a single, centered nucleus. They are also involuntary or not under immediate conscious control. Rather than Z-disks, which join skeletal muscle cells, intercalated disks join cardiac muscle fibers. Cardiac muscles are located only in the heart. Unlike skeletal, cardiac muscle can contract without extrinsic nerve or hormonal stimulation. It contracts via its own specialized conducting network within the heart, with nerve stimulation causing only an increase or decrease in rate of conducting discharge. The heart also has some very beneficial features such as an increased number and larger mitochondria, which allow it to produce more ATP. This is very important since the heart is constantly contracting and relaxing. Cardiac muscle can also convert lactic acid produced by skeletal muscle to ATP. This is quite ingenious since lactic acid is a by-product of muscle when in a deoxygenated state, a state that would...