Parts of the Muscular System
There are three types of muscular tissues: skeletal (or striated) muscle, cardiac muscle, and smooth muscle.
Skeletal muscle is found throughout your body. Anything that you can consciously flex (control voluntarily) is skeletal muscle. Skeletal muscle is also known as striated muscle because, when viewed under the microscope, the muscle has a striped appearance. This goes back to the highly organized muscle structure that is readily visible under an electron microscope.
Cardiac muscle is a specialized striated muscle that makes up your heart. It contracts to pump blood through your body, and it never tires, never stops working until you die. By the age of 70, your heart has been continuously beating more than 2 billion times! Cardiac muscle is involuntary muscle but nerves and hormones can change its contraction in different situations.
Smooth muscle is found around organs such as your stomach, bladder, and uterus. Smooth muscle works independently, without your conscious input, which is important for life-supporting functions such as digestion. Try it: your food does not fall into your stomach because of gravity. It moves because of a process called peristalsis that “waves” the contents of your mouth down your digestive tract even when you do a headstand. The blood vessels in your body are also lined with smooth muscle cells, which enables them to become larger (dilate) or get smaller (contract), as needed. This allows the body to divert the blood to areas of highest need.
A Closer Look at Muscle
Muscle compares to a big rope made up of smaller ropes, which are in turn made up of smaller yarns, and so on. Using this analogy, let’s explore the parts of a large muscle.
Muscles are a collection of myocyte bundles (you will notice frequent use of the prefix “myo-” in this section: it is Greek for muscle; “-cyte” simply means cell). Each myocyte – also referred to as a muscle fiber – contains so-called thin filaments which are made of actin, as well as thick filaments made of myosin. It is the highly intermingled organization of thin and thick filaments that creates the stripes in striated muscle.