Which one of the following statements correctly describes activities of muscles?
How do our bodies move?
Muscle cells are specifically engineered to contract. Muscles permit motions such as walking, as well as bodily functions such as respiration and digestion. Skeletal muscle, cardiac muscle, and smooth muscle are the three types of muscle tissue present in the human body (Figure 19.33).
Graph 19.33. Skeletal muscle, smooth muscle, and cardiac muscle are the three types of muscle tissue present in the human body, and they can all be seen using light microscopy. Smooth muscle cells have only one plump nucleus and are short, tapered at either end. Cardiac muscle cells are short, branched, and striated. The cytoplasm will branch, and the cell has a single nucleus in the middle. (credit: NCI, NIH modification; scale-bar data from Matt Russell)
Skeletal muscle tissue attaches to bones or skin to form skeletal muscles, which regulate locomotion and any movement that can be actively regulated. Skeletal muscle is also known as voluntary muscle because it can be regulated by thought. Skeletal muscles are long and cylindrical in appearance, and skeletal muscle tissue appears striped or striated when viewed under a microscope. The normal arrangement of contractile proteins causes the striations (actin and myosin). Actin is a globular contractile protein that helps muscles contract by interacting with myosin. Multiple nuclei can also be found in a single skeletal muscle cell.
11 major muscle groups
The organization of muscle tissue into sarcomeres gives cardiac muscle, like skeletal muscle, a striated appearance. Although cardiac muscle is similar to skeletal muscle in many respects, it differs in a few ways. Tubular cardiomyocytes, or cardiac muscle cells, make up cardiac muscles. Tubular myofibrils, which are repeating portions of sarcomeres, make up cardiomyocytes. Electrical action potentials are transmitted between sarcomeres through intercalated disks.
In both cardiac and skeletal muscle, a sarcomere is the essential unit of muscle tissue. Sarcomeres appear as striations with alternating dark and light bands under the microscope. T-tubules bind sarcomeres to a plasma membrane called a sarcolemma, which increases the rate of depolarization within the sarcomere.
Sarcomeres are made up of long, fibrous proteins that slide past one another as muscles contract and relax. Myosin, which forms a dense, flexible filament, and actin, which forms a thin, more stable filament, are the two most important proteins in sarcomeres. Myosin has a globular head and a long, fibrous tail that attaches to actin. The head of the myosin also binds to ATP, the energy source for muscle movement. The Z-disc, which forms the sarcomere’s boundaries, binds actin molecules. Myosin and actin combine to form myofibrils, the sarcomeres’ repeating molecular structure.
Introduction to how reflexes work – reflex arc, monosynaptic
When red blood cells (previously equilibrated in a 280-milliosmolar NaCl solution) are put in a solution of 140 millimolar NaCl containing 20 millimolar urea, a relatively large yet permeant molecule, which of the following best describes the changes in cell volume that will occur?
B) The osmolarity of a solution of 140 millimolar NaCl is 280 milliosmoles, which is iso-osmotic to “natural” intracellular osmolarity. Since the intracellular and extracellular osmolarities are equal, there would be no difference in cell volume if red blood cells were put in 140 millimolar NaCl alone. The presence of 20 millimolar urea, on the other hand, raises the osmolarity of the solution, making it hypertonic in comparison to the intracellular solution. Water will initially exit the cell, but since urea is permeable to the plasma membrane, urea will diffuse into the cell and equilibrate through it. As a result, water will re-enter the cell, and the volume of the cell will return to normal.
A-level biology exam technique workshop
Which of the following observations refutes the theory that children inherit traits acquired during their parents’ lifetime? Genetic variation induces variations in the length of the giraffe’s body.
The dominant allele in Mendelian inheritance is for the tall plant, while the recessive allele is for the small plant. Which of the following statements about genotype and phenotype is correct? The tall plant phenotype is represented by the genotypes TT and Tt.
Researchers show that a common topical antibiotic called chloramphenicol prevents a deadly fungal growth on the skin of amphibians in a well-controlled experiment. Which of the following best describes how the antibiotic works to keep a fungal infection at bay? The antibiotic destroys a bacterial partner that is essential for the fungal infection to progress.