Blood, Sweat, and Tears: Human Anatomy

The Muscular System

Types of Muscles

1. Cardiac Muscle
As the name suggests, this is the muscle that makes up the heart. This muscle tends to be very tough and thick to withstand thousands of palpitations every day from birth to death. This muscle is all involuntary so that these palpitations don't need to be controlled consciously. 
2. Skeletal Muscle
This muscle is the muscle that generally covers the extremities (arms, legs, hands, etc.) and is the only voluntary muscle in the body. This is the muscle responsible for the majority of large movement in the body, and is the muscle that moves the bones, adding movement to structure. 

3. Visceral Muscle
This muscle is also involuntary and is often known as smooth muscle. Unlike other types of muscle tissue, smooth muscle is non-striated, meaning that it is not made up of the parallel fibers of actin and myosin. Instead, it's cells are fat in the middle, taper at the ends, and layer over each other. This formation allows for smoother contraction, thus the name smooth muscle. This muscle is what is responsible for all other muscular contractions that are not in the heart or bone, such as the intestines, throat, etc. It is generally found in the torso of the body. 

Functions of Muscles

1. Movement
Obviously, the greatest use of muscles is for their creation of movement. Their contraction on opposite sides of bones pulls your bones in and out to move different parts of your body.
2. Heat Creation
As muscles contract and relax, they expend energy. As with any energy usage, some is lost, and most of what is lost goes to heat. So, muscles indirectly create heat through energy usage, which is important in maintaining homeostasis.