It is and it isn’t, and here are some of the important differences:
Heart muscle — also called cardiac muscle — makes up the wall of the heart. Throughout our life, it contracts some 70 times per minute pumping about 5 liters of blood each minute.
Skeletal muscle, as its name implies, is the muscle attached to the skeleton. It is also called striated muscle. The contraction of skeletal muscle is under voluntary control (voluntary).
Smooth muscle is found in the walls of all the hollow organs of the body (except the heart). Its contraction reduces the size of these structures. Thus it
- regulates the flow of blood in your arteries
- moves food along through your gastrointestinal tract
- expels urine from your urinary bladder
- sends babies out into the world from the uterus
- regulates the flow of air through the lungs
The contraction of smooth muscle is generally not under voluntary control (involuntary).
The heart, responsible for pumping blood throughout the body, is made up of cardiac muscle and is the only place in the body where such muscle is found. All the other muscles in the body are composed of either skeletal muscle or smooth muscle.
Cardiac muscle is unique because it is striated, like skeletal muscle, yet involuntary, like smooth muscle. Skeletal muscle controls the body’s movement and is generally under conscious, or voluntary, control. The internal organs, on the other hand, with the exception of the heart, are made of smooth muscle, which works without conscious effort.
- cardiac muscle cell
- intercalated disks
Cardiac muscle is like skeletal muscle in that it is striated and multinucleate, and like smooth muscle in that the nuclei are centrally located and many cells are required to span the length of the muscle. It differs from both skeletal muscle and smooth muscle in that its cells branch and are joined to one another via intercalated disks. Intercalated disks allow communication between the cells such that there is a sequential contraction of the cells from the bottom of the ventricle to the top. This makes possible the maximal ejection of blood from the ventricle during contraction and occurs without nervous innervation to each cell or group of cells.
Cardiac muscle also differs from the other two muscle types in that contraction can occur even without an initial nervous input. The cells that produce the stimulation for contraction without nervous input are called pacemaker cells.
Hope this helps,