1. Comparative Vertebrate Physiology
Smooth and cardiac muscle

2. Smooth muscle Characteristics lack striations uninucleate
occurs in layers

3. Characteristics Contracts uniquely because
T tubules absent (SR touches sarcolemma)
poorly develop SR (extracellular Ca++)
myosin, actin present lacks troponin

4. Types of smooth muscle Single unit (visceral) occur in layers
gap junctions (spontaneous depolarization)
mechanical stimuli and innervated
visceral organs (gut, bladder etc)

5. Types of smooth muscle Multiunit discrete fibers no gap junctions
innervated
large airways, large arteries, arrector pilli muscles

6. Potentials Single unit Pacemaker, slow wave and action potentials
Multiunit
Spike potentials

7. Smooth muscle contraction
Mechanisms
1. Myosin phosphorylation
Ca++ binds to calmodulin and activates MLCK allowing myosin to bind to actin
2. Regulation by caldesmon
Ca++-calmodulin removes caldesmon from its blocking position on actin
3. Direct Ca++ binding
Binding onto myosin, allowing it to bind to actin

8. Calcium sources Intracellular from SR Extracellular
Voltage operated channel (AP) in multiunit muscle
Tension is maintained after Ca++ is gone

9. Length-tension relationship
Tension over a wide range of initial lengths

10. Contract of smooth muscle
Irregular myofilament arrangement

11. Cardiac muscle Characteristics contains striations
single innervation area by the ANS (pacemaker)

12. Cardiac muscle Characteristics cells are uninucleated
intercalated discs
desmosomes
gap junctions
disc

13. Cardiac muscle Action potentials plateau phase
prolonged refractory period

14. Cardiac muscle Sources of Ca++ Contraction Following contraction
regulated by Ca++
sources: ECF and SR
Following contraction
Ca++ back into SR by Ca++ pump
Ca++ back into ECF by Na+/Ca++ proteins on sarcolemma
Sources of Ca++
Differences between vertebrates (frogs vs. mammals)

15. Intracellular calcium
Factors effecting concentration
1. Degree of depolarization

16. Intracellular calcium
2. Concentration of catecholamines
Ex. epinephrine, norepinephrine, dopamine
-adrenoreceptors activate IP3 increase Ca++ from SR

17. Intracellular calcium
2. Concentration of catecholamines
-adrenoreceptors activate adenyl cyclase increase Ca++ across sarcolemma

18. Intracellular calcium
3. Temperature
Why is heart rate in an ectotherm temperature dependent?
reduction slows Ca++ pump in the SR
reduction slows Na+/Ca++ exchange across sarcolemma