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Table 18.1 Key Differences between Skeletal and Cardiac Muscle Table 18.1 Structure Gap junctions between cells Contracts as a unit T tubules Sarcoplasmic reticulum Source of Ca** for contraction Ca** binds to troponin Pacemaker cells present Tetanus possible Supply of ATP Striated, long, cylindrical, multinucleate No No, motor units must be stimulated individually Abundant Elaborate; has terminal cisterns Sarcoplasmic reticulum only Yes No Yes Aerobic and anaerobic (fewer mitochondria) Key Differences between Skeletal and Cardiac Muscle SKELETAL MUSCLE CARDIAC MUSCLE Striated, short, branched, one or two nuclei per cell Yes Yes, gap junctions create a functional syncytium Fewer, wider Less elaborate; no terminal cisterns Sarcoplasmic reticulum and extracellular fluid Yes Yes No Aerobic only (more mitochondria)