Comparative Vertebrate Physiology

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Presentation transcript:

Comparative Vertebrate Physiology Smooth and cardiac muscle

Smooth muscle Characteristics lack striations uninucleate occurs in layers

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

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

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

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

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

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

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

Contract of smooth muscle Irregular myofilament arrangement

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

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

Cardiac muscle Action potentials plateau phase prolonged refractory period

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)

Intracellular calcium Factors effecting concentration 1. Degree of depolarization

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

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

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