Download Comparative Vertebrate Physiology

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)


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occur in layers
gap junctions (spontaneous depolarization)
mechanical stimuli and innervated
visceral organs (gut, bladder etc)
Types of smooth muscle

Multiunit

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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

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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
Isometric
tension
skeletal
muscle
smooth
muscle
Relative muscle length
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

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

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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
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3. Temperature

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Why is heart rate in an ectotherm temperature
dependent?
reduction slows Ca++ pump in the SR
reduction slows Na+/Ca++ exchange across
sarcolemma