Is the diaphragm a smooth muscle or a skeletal muscle?
Our body has three types of muscles : skeletal, smooth and cardiac.
The skeletal muscle is related to skeletal system, and is voluntary. For example muscles of limbs. Diaphragm is also a skeletal muscle. It is the main muscle of respiration.
The smooth muscle, on the other hand, is found in the wall of blood vessels and viscera (for example in the wall of digestive tract). The cardiac muscle is only found in the heart wall.
Following is a diagram of the diaphragm :