Cardiac Muscle Contraction Mechanism Quiz

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Questions and Answers

What other calcium sources play a role in excitation-contraction coupling?

Sodium ions

Mitochondria (correct)

Chloride ions

Potassium ions

What is the role of Ca++ ions in the regulation of cardiac muscle fiber contraction and relaxation?

Preventing the initiation of contraction

Initiating the action potential

Slowing down the relaxation process

Enhancing the strength of contraction (correct)

How does extracellular Ca++ ions impact the contraction strength of the heart?

Decreases the contraction strength

Halts the contraction process

Increases the contraction strength (correct)

Has no effect on contraction strength

How does intracellular calcium concentration modulate the strength of cardiac muscle contraction?

By activating enzymes that strengthen contraction Signup and view all the answers

What is the function of the actin-binding site in myosin?

Facilitates muscle contraction by interacting with actin Signup and view all the answers

During muscle contraction, what role does troponin play?

Attaches tropomyosin to actin Signup and view all the answers

What covers the actin active site during the resting state of a muscle?

Tropomyosin Signup and view all the answers

Which component of troponin has a strong affinity for calcium ions?

C Signup and view all the answers

During which phase in the cardiac muscle contraction are the L-type Ca++ channels responsible for the depolarization?

Phase 0 Signup and view all the answers

In which portion of the left ventricle does blood flow only occur during diastole?

Subendocardial portion Signup and view all the answers

What is the main source of Ca for cardiac contraction?

Ca from the platue phase Signup and view all the answers

What characterizes the relative refractory period in cardiac muscle?

An action potential can occur, but with a stronger stimulus than usual Signup and view all the answers

Which muscle type depends mainly on ECF Ca for contraction?

Cardiac muscle Signup and view all the answers

How does the relaxation process occur in cardiac muscle?

Ca++ is rapidly pumped back into muscle fibers by SERCA2 pump Signup and view all the answers

What is the role of the transverse tubule (TT) in cardiac muscle contraction?

TT allows direct passage of ions between extracellular spaces and muscle cells Signup and view all the answers

What is the advantage of the long plateau phase in cardiac muscle contraction?

The muscle is more difficult to excite than normal Signup and view all the answers

Study Notes

Calcium Sources in Excitation-Contraction Coupling

Besides the sarcoplasmic reticulum, extracellular Ca++ ions and Ca++ release from the mitochondria also play a role in excitation-contraction coupling.

Regulation of Cardiac Muscle Fiber Contraction and Relaxation

Ca++ ions regulate cardiac muscle fiber contraction by binding to troponin, causing a conformational change that exposes the actin-binding site, allowing myosin to interact with actin and produce contraction.
Ca++ ions also regulate cardiac muscle fiber relaxation by reducing Ca++ ion concentration, allowing troponin to return to its original conformation, blocking the actin-binding site and causing relaxation.

Role of Extracellular Ca++ Ions

Extracellular Ca++ ions impact the contraction strength of the heart by increasing the amount of Ca++ available for contraction.

Intracellular Calcium Concentration

Intracellular calcium concentration modulates the strength of cardiac muscle contraction by increasing or decreasing the amount of Ca++ available for contraction.

Actin-Binding Site and Myosin

The actin-binding site in myosin is involved in muscle contraction by allowing myosin to interact with actin and produce contraction.

Troponin's Role in Muscle Contraction

During muscle contraction, troponin plays a role by undergoing a conformational change upon Ca++ binding, exposing the actin-binding site and allowing myosin to interact with actin.

Resting State of a Muscle

The actin active site is covered by tropomyosin during the resting state of a muscle.

Troponin and Calcium Ions

Troponin-C has a strong affinity for calcium ions, allowing it to detect changes in intracellular calcium concentration.

L-Type Ca++ Channels

L-type Ca++ channels are responsible for the depolarization of the cardiac muscle fiber during the plateau phase.

Blood Flow in the Left Ventricle

Blood flow only occurs during diastole in the apex of the left ventricle.

Main Source of Ca for Cardiac Contraction

The main source of Ca for cardiac contraction is the extracellular fluid (ECF Ca).

Relative Refractory Period

The relative refractory period in cardiac muscle is characterized by the inability of the muscle to contract again due to the refractory period of the L-type Ca++ channels.

Muscle Type and ECF Ca

Smooth muscle depends mainly on ECF Ca for contraction.

Relaxation Process in Cardiac Muscle

The relaxation process in cardiac muscle occurs when Ca++ ion concentration decreases, allowing troponin to return to its original conformation, blocking the actin-binding site and causing relaxation.

Transverse Tubule (TT) in Cardiac Muscle Contraction

The transverse tubule (TT) plays a role in cardiac muscle contraction by allowing rapid depolarization of the muscle fiber, leading to rapid contraction.

Advantage of the Long Plateau Phase

The advantage of the long plateau phase in cardiac muscle contraction is that it allows for longer contraction times, resulting in more forceful contractions.

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Description

Test your knowledge on the source of Ca for cardiac contraction in cardiac muscle cells, the openings of transverse tubules, and the factors influencing the strength of smooth muscle contraction.