4- Compare and contrast the structure, function and control of the three muscle types found in the body.
All muscle tissue shares the same four functional characteristics which are electrical excitability, contractility, extensibility and elasticity. Electrical excitability is the ability to respond to certain stimuli by electrical signals. Contractility is the ability to contract or shorten. Extensibility is the ability to stretch without being damaged. Elasticity is the ability to return to the original length and shape after contraction or extension. In lean adult muscle tissue formulates almost half of body weight. The general functions of muscle tissue are body movements, stabilizing body position, generating heat, storing and moving substances within the body. The three muscle types found in the human body are skeletal muscle tissue, smooth muscle tissue and cardiac muscle tissue. Also, they differ in the structure, function and control. (Tortora and Derrickson, 2006).
The skeletal muscle tissues are usually attached by tendons to the bone and from this location it gets her name. Exception can be found in some facial muscle attached to the skin. skeletal muscles are controlled by the somatic nervous system without pacemaker. The smooth muscles are located in walls of hollow visceral organs except the heart. They can be found in airway, blood vessels, arrectore pili muscles of hair follicles and multiunit muscle in intrinsic eye muscles. The cardiac muscle tissues are located only in the wall of the heart. Both cardiac and smooth muscles are controlled by the autonomic nervous system and both of the cardiac and single unit of the smooth muscle have a pacemaker (Marieb and Hoehn, 2007; Tortora and Derrickson, 2006).
Under microscope, skeletal muscle fiber appears to be long cylindrical shaped and obvious striated with multi peripherally nuclei and no gap junction. The skeletal muscle fiber diameter varies between 10 to 100 μ m and their length varies between100 μ m to 30 cm. The cardiac muscle fiber appears to be branched cylindrical shaped and striated with one or two centrally located nuclei and gap junction between the fibers. The cardiac muscle fiber diameter varies between 10 to 20 μ m and their length varies between 50 to100 μ m. The smooth muscle fiber appears to be thick in the middle where the only nuclei located, narrowed at each end, not striated with no gap junction in multiunit smooth muscles but visceral (single unit) muscle have gap junction between the fibers. The smooth muscle fiber diameter varies between 3 to 8 μ m and their length varies between 30 to200 μ m. The gap junction and pacemaker for both cardiac and the visceral smooth muscle gives them the ability to contract at the same time as one unit (Marieb and Hoehn, 2007; Tortora and Derrickson, 2006).
Skeletal muscle contains three connective tissues. These tissues are endomysium, perimysium and epimysium. Skeletal muscles have Irregular rhythm and slow to fast contraction rate because of that they get tired and must rest. Both the cardiac and the smooth muscles have only endomysium connective tissue and regular rhythm but they differ in the contraction rate. The cardiac muscle has moderate speed of contraction rate, while the smooth muscle has very slow contraction rate (Marieb and Hoehn, 2007; Tortora and Derrickson, 2006).
The smooth muscle lack of transverse tubules and have only small amount of sarcoplasmic reticulum for calcium (Ca2+) storage but have caveolae which contain extracellular fluid full of calcium. The skeletal muscles have two T tubules in each A-I band junctions at the sarcomere and the sarcoplasmic reticulum is the only source of calcium. While in the cardiac muscle there is only one T tubules in each Z disc at the sarcomere and have two source of calcium. These two sources are the sarcoplasmic reticulum and extracellular fluid (Marieb and Hoehn, 2007; Tortora and Derrickson, 2006).
The contractions of skeletal muscles are regulated by acetylcholine released by somatic motor neurons and the ATP is delivered via aerobic and anaerobic respiration. The contractions of both cardiac and smooth muscles are regulated by acetylcholine and norepinephrine released by autonomic motor neurons, stretching and several hormones released by the endocrine glands. Also, oxygen is delivered for both of them via aerobic respiration (Marieb and Hoehn, 2007; Tortora and Derrickson, 2006).
Each type of muscles tissue has designated function. The cardiac muscle function is to pump blood to all parts of the human body. The smooth muscle main function is motion of fluid and substance through the body and responsible of blood vessels constriction and dilatation. The skeletal muscle functions are body movements, protection of vital organs, heat production, stabilizing of joints and posture (Marieb and Hoehn, 2007; Tortora and Derrickson, 2006).
In conclusion, the three types of muscle tissue are skeletal muscle tissue, smooth muscle tissue and cardiac muscle tissue. All muscle tissue shares the same four functional characteristics. The three types muscle tissue differs in the structure, function and control.
Human Bioscience
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