1 Each muscle fibre ( muscle cell ) is covered by a plasma membrane sheath which is called the sarcolemma. 2  Tunnel-like extensions from the sarcolemma pass through the muscle fibre from one side of it to the other in transverse sections through the diameter of the fibre.keletal muscles consist of 100,000s of muscle cells (also known as muscle fibers) that perform the functions of the specific muscle of which they are a part.
Green vegetables are also a major source of iron and calciumfor any diet. Swiss chard and spinach are not considered good sources of calcium, due to their high content of oxalic acid. Green leafy vegetables are rich in beta-carotene, which can also be converted into vitamin A, and also improve immune function. Millions of children around the world have an increased risk of blindness, and other illnesses because of inadequate dietary vitamin A from green leafy vegetables.
Green leafy vegetables and orange vegetables and fruits supply vitamin A in the form of carotenoids. To easily meet your recommended intakes, the Dietary Guidelines for Americans suggests 3 cups per week of dark leafy green vegetables and 2 cups per week of orange vegetables.hat are the best food sources? Preformed vitamin A (a.k.a. retinol) is found in foods of animal origin, such as liver, eggs, milk fortified with vitamin A, fortified cereals and fish.