Heart/skeletal differences

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

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

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

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

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

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

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

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