2. Heart/skeletal differences New slide Skeletal Muscle Long cells Cells independent of each other Cardiac Muscle Short cells Cells connected by desmosomes and gap junctions for strong connection and communication See 673

3. Heart/skeletal differences New slide Skeletal Muscle 2% mitochondria by volume Very regular myofibrils Cardiac Muscle 25%+ mitochondria by volume Myofibrils branch and vary in size (striations less obvious) See 673

4. Heart/skeletal differences New slide Skeletal Muscle T tubules and cisternae result in triads Cardiac Muscle fewer and larger T tubules. No terminal cisternae– no triads See 673

5. Heart/skeletal differences New slide Skeletal Muscle Each cell must be stimulated by nerve in order to fire Motor units fire together Cardiac Muscle some cells fire on their own Organ fires as whole See 673

6. Heart/skeletal differences New slide Skeletal Muscle Shorter contractile phase (from single action potential) shorter refractory period Cardiac Muscle Longer contractile phase from single action potential longer refractory period See 675

7. Heart/skeletal differences New slide Skeletal Muscle Calcium comes from sarcoplasmic reticulum, with action potential. Cardiac Muscle calcium comes mostly from SR (80%) with additional coming from extracellular space (“slow channels”) See 675

8. Heart/skeletal differences New slide Skeletal Muscle Able to function anaerobically Cardiac Muscle anaerobic function quickly shuts down cell (see 675) See 675

9. Heart/skeletal differences New slide Skeletal Muscle Entry of Na + causes depolarization and action potential Cardiac Muscle “leakage” of Na + causes slow depolarization to some threshold which triggers calcium channels to open, causing rapid polarity change See 675 This is about the “autorhythmic” cells