Questions and Answers
Excitation contraction coupling in the myocardial cells is the process where the depolarization wave is propagated over the cardiac muscle fibers then spreads through T-tubules → release of ______ from the terminal cisternae of sarcoplasmic reticulum.
Ca++
The released ______ binds to troponin C.
Ca++
The strength of cardiac muscle contraction is directly proportional to the concentration of ______ in the extracellular fluid.
calcium
Extracellular calcium enters via L-type Ca++ channels during action potential along ______.
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At the end of plateau of cardiac muscle, Ca++ influx is suddenly stopped and active pumping (reuptake) of Ca++ occurs into SR by Ca++ ATP ase, and outside the cell through T tubules by ______-Ca++ exchanger.
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According to Starling's law, an increase in venous return leads to an increase in initial length (EDV) which results in an increase in ______.
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Within certain limits, the greater the initial length of the cardiac muscle fibers, the greater the ______.
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Positive inotropic agents lead to an increase in ______.
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Vagal tone reduces SAN rhythm from 120 beat/min to 70 beat/min, blocking vagus with atropine results in an increase in ______.
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Marked increase in extracellular K+ may stop the heart in ______.
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Study Notes
Excitation-Contraction Coupling in Myocardial Cells
- Depolarization wave spreads through cardiac muscle fibers, initiating contraction.
- Signal travels via T-tubules, leading to calcium release from sarcoplasmic reticulum terminal cisternae.
- Released calcium ions bind to troponin C, facilitating muscle contraction.
Calcium's Role in Contraction Strength
- Strength of cardiac muscle contraction is directly proportional to extracellular calcium concentration.
- Calcium enters myocardial cells through L-type calcium channels during the action potential phase.
Calcium Handling and Reuptake
- At the end of the plateau phase of cardiac muscle action potential, calcium influx ceases.
- Active reuptake of calcium into the sarcoplasmic reticulum occurs via calcium ATPase.
- Calcium is also extruded from the cell through T-tubules utilizing the sodium-calcium exchanger.
Starling's Law and Cardiac Function
- According to Starling's Law, increased venous return results in enhanced end-diastolic volume (EDV).
- Greater initial length of cardiac muscle fibers correlates with increased contraction strength.
- Allows the heart to adjust its output in response to varying levels of venous return.
Effects of Inotropic Agents and Autonomic Regulation
- Positive inotropic agents enhance the strength of muscle contractions by increasing calcium availability.
- Vagal tone reduces the heart rate from 120 beats per minute to approximately 70 beats per minute.
- Atropine administration blocks vagal effects, causing an increase in heart rate.
Effects of Extracellular Potassium Levels
- Significant increases in extracellular potassium can lead to cardiac arrest.
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Description
Test your knowledge on the ability of the cardiac muscle to convert chemical energy into mechanical energy for pumping blood. Explore topics like excitation-contraction coupling in myocardial cells and the process of cross bridge cycling for contraction.
