<prompt> 10 years old Ramu has increasing muscle weakness and raised CPK levels. The most likely defect is in plasma membrane of-NervesMuscle fibresBasement membraneAll body cells  <response>: Ans. is b Muscle fibres Ref. Chandrasoma Taylor, 3e, p. 953.Increase in CPK level with muscle weakness suggests muscle cell damage.Creatine kinase is an enzyme found mainly in:Skeletal muscleHeartBrainIts levels will be raised in the serum when any of the above mentioned cell is damaged.There are various isotypes of the enzyme which are specific for difference cells.Enzyme - TissueCreatine kinase - HeartMB isoenzymeCreatine kinase - BrainBB isoenzymeCreatine kinase - Skeletal muscleMM isoenzymeOther enzymes elevated in muscle diseasesAldolaseAminotransferases specially ACT Lactate dehydrogenase 