3 Types Of Muscle Type
The muscular system functions to inhibit the actions of excitability, contractility, extensibility, and elasticity. The 3 types of muscle tissues are skeletal, cardiac, and smooth muscles. The only muscle type that you can voluntarily control are the skeletal muscles because most of these muscles are attached to the bones of the body which are responsible for movement of the skeletal system. In fact, “While skeletal muscles are under voluntary control, they also may receive some automatic inputs from the brain. This is certainly true of many of the muscles of respiration (breathing), which are automatically programmed to continue contracting and relaxing, so that an individual does not have to decide to take each breath. There are more than 650 different voluntary muscles in the human body" (World of Anatomy and Physiology, 2007 [Source #1]). The cardiac tissue located in the cardiac muscle is responsible for the forceful contraction of heart beats. The result of the heartbeat is that the heart essentially pumps out the used blood. Smooth muscle makes up the muscles of the intestine, the uterus, the blood vessels, and the eyes. The intestine contracts and relaxes without an individual being aware of its actions, allowing for food to be churned up and moved along its length. An individual cannot exert control over these muscles, meaning, one cannot decide to speed up the amount of time it takes for a meal to travel down the length of intestine.
The three types of muscle fibers: skeletal muscle fiber, smooth muscle fiber, and cardiac muscle fiber. (Experiment Central, 2010)
Muscle Tissue Regeneration
Of the three types of muscle tissue, smooth muscle tissue has the greatest capacity for regeneration. Pericytes are the stem cells of smooth muscle and are capable of regenerating small blood vessels that consist of smooth muscle. Pericytes are basically a connective tissue cell that occurs about small blood vessels. However, muscle tissue damage can occur in all three types of muscle tissue: skeletal, cardiac, and smooth muscle. Skeletal muscle tissue is susceptible to damage from strenuous exercise. In particular, eccentric exercises that include muscle lengthening cause fatigue more rapidly than concentric exercises that include muscle shortening - leading to more muscle damage. Also, “Blood vessels and nerves are important factors in the regeneration of muscle tissue. If vascularization is absent, macrophages will be unable to reach the damaged area, and the healing process will be halted. Additionally, any living cells will die within hours if blood is absent from the injured region. In the case of severe skeletal muscle damage, fibrosis can occur, interrupting contraction of skeletal muscle. Fibrosis is the development of scar tissue in place of muscle fibers; it limits the ability of muscle tissue to regenerate" (World of Anatomy and Physiology, 2007 [Source #2]). Macrophages, a type of white cell, release a hormone called prostaglandin that is believed to stimulate the sensory nerves in muscles, creating pain and inflammation. Prostaglandin are basically fatty acids or lipids found produced by nearly every cell in the body and function to do many things as there many, different kinds. Muscles are usually the most sore two to three days following exercise and are not fully healed until eight to ten days post exercise (2007). During repair, muscle tissue becomes resistant to damage from further strenuous exercise.
Muscle Energy
“Skeletal muscles are the mechanism for powering human movement. While individual muscles are typically regarded as distinct organic structures, the skeletal muscles are the largest organ grouping in the body (the skin is the largest contiguous organ)" (World of Sports Science, 2007). All joints are, essentially, moved by pairs of muscles working in contrasting but complementary ways. These are called antagonistic muscles which are basically muscles that opposes the action of another. Antagonistic pairs are needed in the body because muscles can only exert a pulling force, and can't push themselves back into their original positions. Also, “The energy metabolism characteristics of each type of fiber also contribute to the function of each type. Glycogen, the storage form of the carbohydrate product glucose, is then utilized at the muscle in the cycle of electrochemical reactions that produce adenosine triphosphate (ATP), the source of energy within the muscle" (World of Sports Science, 2007). The mitochondria is the portion of the muscle cell where the energy production occurs. It is within the mitochondrial membrane where, depending on the energy sources that are available at the moment, either fatty acids are reduced for energy production or glucose is converted to lactate (lactic acid) as a part of the ATP energy cycle. Cellular respiration in the presence of oxygen, or aerobic respiration, is the process in which organic substrates are broken down into carbon dioxide and water, causing the release of a considerable amount of energy in the form of ATP.
ADP is formed during cellular respiration with energy released by the breakdown of glucose molecules as well as the release of energy to the muscle for contraction. (The Gale Encyclopedia of Science, 2010)
Muscle Excitation and Stimuli
Muscle excitability is basically the ability of a muscle fiber to respond to a stimulating agent. This means that the muscle fiber is able to receive and respond to any change in the environment, whether it be inside or outside of our bodies. Both factors go hand in hand. When skeletal muscles contract, they help the body with mobility and breathing. Skeletal muscles respond to stimuli that are both voluntary and involuntary. Although similar to skeletal muscle, cardiac muscle is only unique to the heart. Cardiac cells are smaller and contain more mitochondria than a skeletal muscle cell. In fact, "The mitochondria produce high-energy molecules in the form of ATP to supply cardiac muscles with the fuel they need to continuously contract, pumping blood through the circulatory system" (McFarlane-Parrott, 2007). The heart is an involuntary muscle and does not need any help from the nervous system to initiate and maintain contraction. Smooth muscles are controlled involuntarily. Smooth muscle lines the walls of the body's organs, particularly the blood vessels and digestive system. When smooth muscles contract, they control the passage of substances through blood vessels and intestines (2007). Muscle contractions involve the shortening of a muscle while exerting a force at the same time and performing work. It should be noted thought that while skeletal muscles are resting, there is still a force acting which is created from the muscle's connection to the bone on each end of the muscle. This force is basically a tension force where something is being stretched, similar to the force of a rubber band that is stretched.