MEDizzy - During a physiology experiment, a muscle is extracted and

Feed Library Learning Discuss Leaderboard Journal

Musculoskeletal and Integumentary Systems

During a physiology experiment, a muscle is extracted and suspended in a physiologic solution. The muscle contracts when directly stimulated with an electrode, but it does not contract spontaneously. It continues to contract upon stimulation after being treated with a drug that antagonizes myosin light chain kinase activity, and after it is placed in new salt solution that is calcium-free. Based on the experimental data provided, what type of muscle tissue is most likely being tested?

ExplanationThe muscle tissue being tested contracts when stimulated with an electrode, even in the absence of extracellular calcium, which indicates skeletal muscle tissue. (A) Cardiac muscle has automaticity, which allows the muscle to spontaneously contract without any electrical or hormonal stimuli. It also requires extracellular calcium influx through the dihydropyridine receptor (DHP) to open the ryanodine receptors (RyR) on the sarcoplasmic reticulum for substantial cytoplasmic calcium increases (calcium-induced calcium release). Therefore, because the experimental muscle tissue does not contract spontaneously and because it does contract in the absence of calcium, cardiac muscle tissue is excluded. (B, D) Smooth muscle tissue requires phosphorylation of myosin light chain (MLC) by myosin light chain kinase (MLCK) for contraction to occur. Because the experimental muscle tissue continues to contract when antagonized by a drug that blocks MLCK, this excludes smooth muscle tissue.