WEEK 8 MRAD 2235 Anatomy & Physiology of Cardiac Conduction System

These flashcards cover the key concepts and mechanisms of the cardiac conduction system and its components, including pacemaker and contractile cells, their functions, and the electrical events leading to heart contractions.

What are the two types of cardiac myocytes involved in the heartbeat?

Contractile cardiomyocytes and autorhythmic cells.

What is the role of pacemaker cells in the heart?

To generate rhythmic action potentials that set the heart rate.

How do autorhythmic cells generate action potentials?

They spontaneously and rhythmically generate and conduct action potentials.

What is the intrinsic rate of the SA node?

Approximately 100 action potentials per minute.

Where is the SA node located?

In the right atrium of the heart.

What happens when the SA node generates an action potential?

It causes depolarization of connected cardiac myocytes and stimulates contraction of the atria.

What is the function of the AV node?

It allows for delayed conduction to let the atria finish contracting before the ventricles contract.

What structure prevents the electrical signal from passing directly from the atria to the ventricles?

The septum.

What are Purkinje fibers responsible for?

Transmitting the wave of excitation throughout the ventricles.

What kind of channels do pacemaker cells possess that aid in action potential generation?

Voltage-gated Na+ 'funny' channels and T-type Ca2+ channels.

What type of heart myocyte has relatively few myofibrils?

Autorhythmic cells.

How does the cardiac conduction system ensure correct timing in heartbeats?

It dictates how electrical signals spread through the cardiac chambers.

What happens during the rising phase of the pacemaker action potential?

Ca2+ channels open, allowing rapid Ca2+ influx.

What initiates the depolarization of the SA node?

The spontaneous closure of K+ channels and opening of Na+ channels.

What is the role of Bachmann’s bundle in the conduction system?

It fast-tracks depolarization from the SA node to the left atrium.

What is the effect of norepinephrine on heart rate?

It increases the heart rate by making the SA node fire more rapidly.

What happens when the SA node is damaged?

The AV node can take over as the pacemaker but with a slower firing rate.

What is the purpose of an artificial pacemaker?

To generate electrical impulses to coordinate heart contractions when the natural rhythm is disrupted.

How do larger diameters of cells affect conduction velocity?

They typically contribute to faster conduction velocities.

What ions can affect heart function?

Electrolytes such as sodium (Na+), potassium (K+), and calcium (Ca2+).

What is the relationship between myofibrils and contractile capabilities in cardiomyocytes?

More myofibrils allow for a greater ability to contract.

Why is there a gap between the atria and ventricles in terms of electrical conduction?

To prevent simultaneous contraction, allowing optimal ventricle filling.

What characterizes the action potential of pacemaker cells compared to other excitable cells?

In pacemaker cells, Ca2+ influx rather than Na+ influx drives the rising phase.

What anatomical feature allows for the separation of left and right bundle branches in the conduction system?

The interventricular septum.

What can modulate the heart rate besides the intrinsic firing rate of pacemakers?

The autonomic nervous system and hormonal influences.

What happens during repolarization of pacemaker cells?

K+ channels open, leading to K+ efflux and a return to resting potential.

What is the estimated conduction velocity of the SA node action potential?

Approximately 6 m/sec.

What effect do thyroid hormones have on the heart?

They can increase heart rate.

How does the heart's electrical conduction system ensure rapid and coordinated contraction?

Through the precise propagation of electrical impulses via specialized pathways.

What modifications can change the rate of action potential firing of the SA node?

Autonomic innervation and circulating hormones.

Why are pacemaker cells considered electrically self-excitable?

They can generate action potentials independently of nervous stimulation.

What physical structure connects the atria and ventricles in the conduction system?

The AV node.

What is the primary function of contractile cardiomyocytes?

To contract and propel blood through the heart.

What distinguishes the action potential pattern of autorhythmic cells from contractile cardiomyocytes?

Autorhythmic cells have unstable resting potentials leading to spontaneous depolarization.

What happens to K+ efflux after repolarization in pacemaker cells?

K+ channels close, initiating the slow depolarization that prepares for the next action potential.

What role does the cardiac skeleton play in the conduction system?

It acts as an electrical insulator between atria and ventricles.