How does rapid depolarisation occur in ventricular contractile cells?
Rapid depolarization occurs due to the opening of voltage-gated fast Na+ channels, allowing Na+ to enter the cell.
Explain the components of the hearts conducting system.
Components include the SA node, AV node, internodal pathways in the atria, AV bundle (bundle of His), bundle branches, and Purkinje fibers.
How do desmosomes contribute to cardiac muscle function?
Desmosomes prevent cell separation during contraction in cardiac muscle cells.
What is the refractory period in the heart and why is it important?
Refractory period in the heart is when the membrane does not respond normally to a second stimulus to prevent tetanus in the ventricles and ensure coordinated contraction-relaxation cycles.
What are the two types of cardiac muscle fibers?
Contractile fibers and autorhythmic fibers.
What are autorhythmic fibers and what role do they play?
Autorhythmic fibers are self-excitable cells that act without external stimulation, setting the rhythm of the heart as pacemakers and conducting impulses throughout the heart.
What is the sequence of excitation in the heart from the SA node to ventricular depolarization?
SA node generates impulses, impulses move through internodal pathways, pass through AV node, conduct to the AV bundle (bundle of His), branch into bundle branches, and further to Purkinje fibers for ventricular contraction.
What is the resting potential of ventricular and atrial cells?
Resting potential of a ventricular cell is about -90 mV, and for an atrial cell is about -80 mV.
Describe the process of repolarization in cardiac contractile cells.
Repolarization occurs when K+ channels open, allowing K+ to leave the cell, leading to the return of the membrane potential to resting levels.
What happens during the plateau phase of the action potential in cardiac cells?
During the plateau phase, there is increased intracellular Ca2+ which balances the exit of Na+ and keeps the membrane potential at 0mV.
Explain the phases of the action potential in ventricular contractile fibers.
The phases include rapid depolarization, plateau phase, and repolarization.
What is the function of contractile fibers in the heart?
Contractile fibers are responsible for the powerful contractions that drive the hearts pumping activity.
Why do cardiac muscle cells have many mitochondria?
Cardiac muscle cells have many mitochondria to support aerobic metabolism due to the high energy demands of the heart.
How is the contraction of contractile cells similar to skeletal muscle?
Both involve electrical activity (action potentials) leading to mechanical response (contraction), but in cardiac cells, there are two sources of Ca2+: intracellular SR and extracellular.
What are nodal rhythmic fibers and how do they function?
Nodal rhythmic fibers are self-excitable fibers that depolarize spontaneously, leading to the initiation and regulation of the hearts rhythm.
Define and differentiate between premature atrial contractions and paroxysmal atrial tachycardia.
Premature atrial contractions are single early heartbeats caused by atrial cells triggering outside the normal rhythm, while paroxysmal atrial tachycardia is a rapid increase in heart rate due to a flurry of atrial activity.
What are the characteristics of cardiac muscle cells?
Small, single central nucleus, branching interconnections between cells, many mitochondria, same actin/myosin setup as skeletal muscle cells.
What are intercalated disks in cardiac muscle cells?
Branching interconnections between cells that contain desmosomes and gap junctions for cell-cell communication.
What is the significance of gap junctions in cardiac muscle cells?
Gap junctions allow ions and action potentials to pass from cell to cell, electrically coupling the myocardium and ensuring coordinated contraction.
Describe the characteristics of autorhythmic fibers in the heart.
Autorhythmic fibers depolarize and reach threshold spontaneously, controlling and coordinating the heartbeat automatically.
