<span>There are numerous proteins in muscle. The main two are thin actin filaments and thick myosin filaments. Thin filaments form a scaffold that thick filaments crawl up. There are many regulatory proteins such as troponin I, troponin C, and tropomyosin. There are also proteins that stabilize the cells and anchor the filaments to other cellular structures. A prime example of this is dystrophin. This protein is thought to stabilize the cell membrane during contraction and prevent it from breaking. Those who lack completely lack dystrophin have a disorder known as Duchene muscular dystrophy. This disease is characterized by muscle wasting begininng in at a young age and usually results in death by the mid 20s. The sarcomere is the repeating unit of skeletal muscle.
Muscle cells contract by interactions of myosin heads on thick filament with actin monomers on thin filament. The myosin heads bind tightly to actin monomers until ATP binds to the myosin. This causes the release of the myosin head, which subsequently swings foward and associates with an actin monomer further up the thin filament. Hydrolysis and of ATP and the release of ADP and a phosphate allows the mysosin head to pull the thick filament up the thin filament. There are roughly 500 myosin heads on each thick filament and when they repeatedly move up the thin filament, the muscle contracts. There are many regulatory proteins of this contraction. For example, troponin I, troponin C, and tropomyosin form a regulatory switch that blocks myosin heads from binding to actin monomers until a nerve impulse stimulates an influx of calcium. This causes the switch to allow the myosin to bind to the actin and allows the muscle to contract. </span><span>
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Answer:
b. Exchange between the plasma and the intracellular fluid occurs across the cell membrane.
Explanation:
The body fluid can be categorized as extracellular and intracellular fluid. The fluid within cells is called intracellular fluid and the body fluid outside body cells makes the extracellular fluid. The interstitial fluid is the extracellular fluid that is present in the narrow spaces between cells of tissues.
On the other hand, the extracellular fluid present within blood vessels is termed blood plasma. Therefore, plasma and intracellular fluid can exchange material via interstitial fluid only, not directly via the cell membrane. The exchange between interstitial fluid and intracellular fluid occurs across the cell membrane.
Salt or bad products that enters ur body
