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.
This chart will help you find foods that are a good source of vitamin A. Both animal and plant foods have vitamin A activity. Retinol, also called preformed vitamin A, is the natural form found in animals.Carotenoids, found in plants, are compounds that the body can convert to vitamin A.Liver is the single best food source of vitamin A. However, many experts recommend eating liver only once or twice a month because of the toxic substances it can contain. Environmental pollutants tend to congregate in an animal's liver.oth animal and plant foods have vitamin A activity. Retinol, also called preformed vitamin A, is the natural form found in animals. Carotenoids, found in plants, are compounds that the body can convert to vitamin A.