18 Questions
What is the role of ATP in muscular contraction and relaxation?
ATP breaks down to supply energy for muscular contraction and relaxation.
Which step involves the sliding of thin filaments over thick filaments in muscular contraction?
Step 6: Shortening obtained by disconnection and reconnection of myosin heads.
During muscular relaxation, what leads to the cessation of myosin and actin interaction?
Reuptake of calcium by the sarcoplasmic reticulum.
Which process uncovers the binding sites of myosin on actin filaments during muscular contraction?
Release of calcium ions from lateral sacs of the sarcoplasmic reticulum.
Which structure is responsible for spreading action potential to the depth of myofibrils?
T-tubular system
In which step is more shortening obtained by disconnection, cocking, reconnection, and swiveling of myosin heads on actin filaments?
Step 5: Sliding of thin filaments over thick filaments.
What is the role of the sympathetic nervous system in cardiac muscle contraction?
Activates β1-adrenoceptors
How does physiological stimulation via sympathetic nerves affect the rate of relaxation in cardiac muscle?
Accelerates Ca++ re-entry into the SR
Which protein undergoes phosphorylation due to the activation of β1-adrenoceptors?
Phospholamban
How do drugs like milrinone and caffeine affect cAMP levels?
Inhibit phosphodiesterases
What effect does increasing intracellular [Ca++] have on cardiac muscle contraction?
Increases force of contraction
How does phosphorylation of phospholamban influence Ca++ levels in the sarcoplasmic reticulum?
Increases Ca++ retention in the SR
Where does the majority of the Ca++ used to trigger contraction of cardiac muscle come from?
Sarcoplasmic reticulum (SR)
In which type of muscle does the source of Ca++ for the contractile mechanism differ from cardiac muscle?
Skeletal muscle
What triggers an initial increase in intracellular calcium ion [Ca++i] concentration in cardiac muscle cells?
Inward flow of calcium from extracellular fluid
What role do L-type calcium channels play in cardiac muscle contraction?
Mediate inward flow of extracellular calcium
Which component helps spread electrical excitation rapidly into cardiac muscle cells?
T tubules
What type of muscle uses only sarcoplasmic reticulum (SR) stores of Ca++ for contraction?
Skeletal muscle
Explore the factors influencing the force of cardiac muscle contraction, including the role of crossbridges and intracellular calcium levels. Learn how sympathetic nervous system activation and certain drugs can enhance cardiac muscle contraction. Test your knowledge on physiological stimulation in cardiac muscle.
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