Passage
The nicotinic acetylcholine receptor (nAChR) is a protein embedded in the muscle fiber membrane that facilitates cell-to-cell communication across the neuromuscular junction. When acetylcholine (ACh) binds nAChR, electrical depolarization within skeletal muscle fibers is induced and ultimately gives rise to contractile activity. The nAChR is composed of five protein subunits symmetrically organized around a central ion pore. Previous studies demonstrated that these subunits may serve as epitopes (antibody binding sites) in autoimmune disease. By reversibly binding nAChR subunits, anti-nAChr antibodies may temporarily block the attachment site for ACh, resulting in muscle weakness.Researchers harvested muscle samples from mice to investigate the effects of anti-nAChR antibodies on muscle tension, the pulling force transmitted by muscles during contraction.Experiment 1First, skeletal muscle samples (tibialis anterior) of adult male mice were surgically harvested (n = 30) , washed, and stripped of connective tissues. Next, the isolated muscle samples were placed in a 150-mL oxygen-infused, electrolyte-rich bath containing glucose and Ca²⁺ ions that were able to enter the muscle fibers and enable maximal contractile force. One end of the submerged muscle was anchored in place while the other was attached to an apparatus that measures muscle tension and modifies muscle length. Using electrodes, action potentials were elicited in the harvested muscle tissue to evaluate contractile function (Figure 1) .
Figure 1 Action potential elicited from a harvested skeletal muscle sampleExperiment 2The researchers divided the 30 muscle samples into three groups of 10. Resting muscle tension was measured, and the electrolyte-rich baths of each group were further infused with a 7.5-mL solution containing mouse-specific anti-nAChR antibodies, ACh, or a mixture of both (Table 1) . Post-infusion (peak) muscle tension was measured for 30 minutes, with results displayed in Figure 2.Table 1 Solutions Infused into the Electrolyte-Rich Bath
Figure 2 Pre-infusion resting muscle tension and post-infusion peak muscle tension in harvested muscle samples (Note: * indicates p < 0.05.)
-To interpret the results of Experiment 2, researchers must assume that:muscle samples were of uniform weight and size.no intermolecular interactions occurred between ACh and anti-nAChR antibodies in Infusion C.co-infusion of ACh and anti-nAChR antibodies was performed following ACh infusion.

Question

Passage
The nicotinic acetylcholine receptor (nAChR) is a protein embedded in the muscle fiber membrane that facilitates cell-to-cell communication across the neuromuscular junction. When acetylcholine (ACh) binds nAChR, electrical depolarization within skeletal muscle fibers is induced and ultimately gives rise to contractile activity. The nAChR is composed of five protein subunits symmetrically organized around a central ion pore. Previous studies demonstrated that these subunits may serve as epitopes (antibody binding sites) in autoimmune disease. By reversibly binding nAChR subunits, anti-nAChr antibodies may temporarily block the attachment site for ACh, resulting in muscle weakness.Researchers harvested muscle samples from mice to investigate the effects of anti-nAChR antibodies on muscle tension, the pulling force transmitted by muscles during contraction.Experiment 1First, skeletal muscle samples (tibialis anterior) of adult male mice were surgically harvested (n = 30) , washed, and stripped of connective tissues. Next, the isolated muscle samples were placed in a 150-mL oxygen-infused, electrolyte-rich bath containing glucose and Ca²⁺ ions that were able to enter the muscle fibers and enable maximal contractile force. One end of the submerged muscle was anchored in place while the other was attached to an apparatus that measures muscle tension and modifies muscle length. Using electrodes, action potentials were elicited in the harvested muscle tissue to evaluate contractile function (Figure 1) .

Figure 1 Action potential elicited from a harvested skeletal muscle sampleExperiment 2The researchers divided the 30 muscle samples into three groups of 10. Resting muscle tension was measured, and the electrolyte-rich baths of each group were further infused with a 7.5-mL solution containing mouse-specific anti-nAChR antibodies, ACh, or a mixture of both (Table 1) . Post-infusion (peak) muscle tension was measured for 30 minutes, with results displayed in Figure 2.Table 1 Solutions Infused into the Electrolyte-Rich Bath

Figure 2 Pre-infusion resting muscle tension and post-infusion peak muscle tension in harvested muscle samples (Note: * indicates p < 0.05.)
-To interpret the results of Experiment 2, researchers must assume that:muscle samples were of uniform weight and size.no intermolecular interactions occurred between ACh and anti-nAChR antibodies in Infusion C.co-infusion of ACh and anti-nAChR antibodies was performed following ACh infusion.

Quizplus · Accepted Answer

11ecba2d_100e_73f0_a3bf_67b4f5194b7b_MD0008_00 The two primary variables in an experiment are the dependent variable and the independent variable. The general experimental goal is to investigate the relationship between these two variables by intentionally modifying the independent variable and observing the effect of this modification on the dependent variable. In Experiment 2, the researchers studied how three infusions, each containing different combinations of acetylcholine and anti-nAChR antibodies, affected the tension of muscle samples when added to an electrolyte-rich bath. The infusion type was intentionally modified, and therefore was the independent variable. Muscle tension, which was assessed in each infusion, served as the dependent variable. However, some experimental variables can have an unforeseen effect on the independent variable or dependent variable, complicating any interpretation of a possible relationship between the two. Such variables are referred to as confounding variables. Ideally, confounding variables should be either controlled for or eliminated from an experimental design. Failure to do so may impair a researcher's ability to reach valid conclusions about experimental results. Accordingly, to interpret the results from Experiment 2, the researchers must have made the following assumptions about potential confounding variables: Muscle samples were of uniform (similar) weight and size. If the muscle samples had varying weights and sizes, the muscle tension measurements could not be compared in a valid manner because larger muscles would generate more tension than smaller muscles (Number I). No intermolecular interactions occurred between ACh and anti-nAChR antibodies in Infusion C. If interactions were to occur, this could interfere with muscle tension measurements as contraction is dependent on ACh binding to its receptor (Number II). (Number III) Experiment 2 was conducted on three groups of 10 unique animal subjects. Isolated muscle samples from each group were exposed to the contents of only one infusion (A, B, or C). At no point in time were these three groups treated with multiple infusions. Educational objective: An ideal experiment features an independent variable, a dependent variable, and no confounding variables.

Passage the Nicotinic Acetylcholine Receptor (NAChR) Is a Protein Embedded in in the Muscle