Cardiac muscle & Conducting system_241105

Name the two circulatory circuits in the heart.

Pulmonary and systemic circulation.

Define automaticity in cardiac muscle cells.

The ability to generate action potentials without external stimuli.

What is the role of contractile cells in the heart?

They perform mechanical contraction, accounting for 99% of heart muscle cells.

What do autorhythmic cells do?

Initiate and conduct action potentials, setting the heart’s rhythm.

What is cardiac rhythmicity?

The heart’s ability to generate action potentials at a regular rhythm, causing consistent muscle contractions.

Describe the structure of cardiac muscle fibers.

Striated, branched, with intercalated discs allowing rapid ion diffusion (presence of gap junctions).

What is the function of intercalated discs?

They facilitate rapid ion movement, allowing coordinated muscle contraction.

What are the two syncytia in the heart?

• Atrial syncytium and ventricular syncytium.

Explain the property of conductivity in cardiac cells.

Ability to transfer action potentials to neighboring cells.

What initiates the heart’s pacemaker potential?

Gradual Na+ influx, reduced K+ outflow, and Ca2+ entry.

Where is the SA node located?

In the right atrium, near the superior vena cava.

What is the function of the AV node?

It delays impulses, allowing the atria to contract before the ventricles.

What is the role of the Bundle of His?

Transmits impulses from the AV node to the ventricles.

How do Purkinje fibers assist in heart contraction?

They distribute impulses quickly across the ventricles for a coordinated contraction.

Describe the initial depolarization phase in contractile cells.

Na+ channels open, causing rapid influx and cell depolarization.

What occurs during the plateau phase in contractile cells?

K+ efflux fast causing repolarisation but Ca2+ influx maintains depolarization, extending the contraction.

What is the purpose of the refractory period in cardiac muscle?

Prevents immediate re-excitation, allowing coordinated contraction and relaxation.

How does sympathetic stimulation affect the heart?

Increases heart rate, force, and AV node conduction speed.

What effect does parasympathetic stimulation have on heart rate?

It decreases heart rate by reducing SA and AV node excitability.

What causes the long action potential in cardiac muscle?

The opening of slow Ca2+ channels creates a plateau phase.

Which ions are involved in pacemaker potential?

Na+, K+, and Ca2+ ions.

What ion movement causes the rising phase of the action potential?

Ca2+ influx through L-type channels in autorhythmic cells.

Why is the plateau phase important?

It prolongs contraction, ensuring efficient blood ejection.

What is the SA node’s discharge rate?

70-80 beats per minute.

What is the resting membrane potential of cardiac contractile cells?

Around -90 mV, maintained by the Na+-K+ pump.