heart electrical Flashcards
What is automaticity in the heart?
The ability of the heart to generate its own electrical impulses automatically.
This allows the heart to beat without needing external signals.
What is the function of the Sinoatrial (SA) Node?
It is the primary ‘pacemaker’ of the heart that initiates the electrical impulse, setting the rhythm for the heartbeat.
This is known as sinus rhythm.
What are secondary pacemakers in the heart?
Cells in the AV node and Purkinje fibers that can take over if the SA node fails.
They have a slower rate than the SA node but can maintain the heartbeat.
What is diastolic depolarization?
The slow, spontaneous depolarization that happens between heartbeats in pacemaker cells.
Pacemaker cells do not have a true resting membrane potential.
What triggers inward Na+ currents during diastolic depolarization?
Hyperpolarization, which causes a gradual buildup of positive charge inside the cell.
This is part of the process leading to action potential initiation.
What happens when the membrane potential reaches -40mV?
Voltage-gated calcium (Ca2+) channels open, triggering the action potential.
This is a critical step in the process of depolarization.
What causes repolarization in pacemaker cells?
The opening of voltage-gated potassium (K+) channels allows K+ to exit the cell.
This returns the membrane to a more negative state after the action potential peaks.
What are funny Na+ channels?
Channels that allow Na+ to flow into the cell, contributing to slow depolarization.
They help bring the membrane potential up to the threshold for action potential initiation.
What effect does sympathetic stimulation have on heart rate?
Increases heart rate by releasing epinephrine or norepinephrine, which opens more HCN channels.
This allows more Na+ ions to enter the cell, speeding up depolarization.
What is the role of acetylcholine in heart rate modulation?
It slows the heart rate by binding to M. AchR receptors, causing K+ channels to open and allowing K+ to leave the cell.
This slows the depolarization process.
What heart rate is typically considered normal resting heart rate?
Around 60-70 bpm.
This rate can increase with sympathetic stimulation.
What indicates a heart rate greater than 100 bpm?
An increase in Na+ influx due to strong sympathetic stimulation or other factors.
This is often a response to physical activity or stress.
What is the maximum heart rate (Max HR) formula?
Max HR = 220 - Age.
This formula is used to estimate the highest number of heartbeats per minute during intense exercise.
What is the target heart rate zone for effective cardiovascular workouts?
50-80% of Max HR.
This range helps improve heart and lung fitness while avoiding overexertion.
What is the resting membrane potential of cardiac muscle cells?
Around -90 mV.
This is similar to other excitable cells.
What occurs during the plateau phase of cardiac muscle action potential?
A slow influx of Ca2+ through voltage-gated Ca2+ channels causes the membrane potential to remain stable for 200-300 ms.
This prevents summation or tetanus, allowing proper relaxation between beats.
How does repolarization occur in cardiac muscle?
Through the opening of voltage-gated K+ channels, allowing K+ ions to exit the cell.
This returns the cell to its resting potential.
What is a key difference between cardiac and skeletal muscle action potentials?
Cardiac muscle has a plateau phase, while skeletal muscle does not.
The plateau phase is crucial for preventing tetanus in the heart.
What happens at the Atrioventricular (AV) node?
The electrical impulse slows down, allowing the atria to fully empty into the ventricles before contraction.
This delay is important for coordinated heart function.
How long after atrial contraction do the ventricles typically contract?
0.1–0.2 seconds.
This timing ensures that the ventricles are filled with blood before pumping it out.
What is the role of gap junctions in cardiac tissue?
They allow action potentials to spread between cardiac cells for coordinated contraction.
This is essential for effective heart function.
