<prompt> Which of the following is an intracellular constituents of neuromuscular system?MgCaClNa  <response>: The nerve and muscle fibers, like other bodily cells, maintain a fluid internal environment that is distinctly different from the external or interstitial medium. The main intracellular constituents are potassium K, magnesium Mg, and phosphorus P, whereas those outside the cell are sodium Na, calcium Ca, and chloride Cl. Ref: Ropper A.H., Samuels M.A. 2009. Chapter 45. Electrophysiologic and Laboratory Aids in the Diagnosis of Neuromuscular Disease. In A.H. Ropper, M.A. Samuels Eds, Adams and Victors Principles of Neurology, 9e. 