There are three main types of muscles in the human body. Skeletal muscles are responsible for movement, stability, heat production, and the regulation of blood glucose levels; cardiac muscles are responsible for pumping blood throughout the body; and smooth muscles are responsible for involuntary movements of internal organs.
Skeletal muscles work together with the skeletal system to support and move the body. Skeletal muscles are composed of striated muscle tissues under control of the somatic, or voluntary, nervous system. In addition to moving the body, skeletal muscles can produce heat through rapid contractions or shivering. Skeletal muscles also regulate blood glucose levels through glucose uptake.
Cardiac muscles are the muscles responsible for the pumping action of the heart. Cardiac muscle is striated like skeletal muscle; but unlike skeletal muscle, it is not under voluntary control. It is controlled by the autonomic, or involuntary, nervous system. Cardiac muscle tissue is also called myocardium and is made of cells called cardiomyocytes. A cardiomyocyte is a muscle cell that is found in cardiac muscle and generates the heart contractions. Cardiomyocytes are connected through junctions, called intercalated discs. These junctions allow the electrical activation that causes all cardiomyocytes to contract as a single unit.Smooth muscle tissue is also controlled by the autonomic nervous system. Smooth muscle is responsible for the involuntary movement of internal organs. For example, movements of the stomach, intestines, and bladder are all caused through smooth muscle contractions. The walls of blood vessels also contain smooth muscles.
Muscle Tissue Types
Similar to skeletal muscle, cardiac muscle has striations and contracts when the filaments slide past each other. However, cardiac cells have a different appearance than skeletal or smooth muscle cells, in that they interconnected, short, and fat. They also have many branches coming off of them. The number of nuclei also differs, having one or two of them. Some cardiac muscle cells can contract on their own, without any neural input. The contraction is also all or nothing. Either all of the heart muscle cells contract at the same time, or none of them contract at all.
Comparison of Muscle Tissue Types
|Body location||Attached to the bones or to the skin||Walls of the hollow organs, eyes, air passages, and large arteries||Only in the heart|
|Cell shape and appearance||Form striations, have multiple nuclei, very long and thin||Form no striations, have single nucleus, spindle shaped||Form some striations, have single or double nuclei, create branching chains|
|Connective tissue components||Epimysium, perimysium, and endomysium||Endomysium||Endomysium attached to heart|
|Regulation of contraction||Voluntary, somatic nervous system||Involuntary, pacemaker cells or autonomic nerves, regulated by local chemicals, hormones, and stretch||Involuntary, pacemaker cells or autonomic nerves, regulated by autonomic nervous system, hormones, stretch|
|Speed of contraction||Slow to fast||Very slow||Slow|
|Metabolism||Aerobic and anaerobic||Mostly aerobic||Aerobic|