eletrical heart activity

Can the heart depolarize without nervous input?

Yes, it is autorhythmic (intrinsic conduction system).

What modifies heart rhythm externally?

Autonomic nervous system (ANS).

What coordinates a heartbeat?

Gap junctions + intrinsic conduction system.

What are autorhythmic cells?

Noncontractile cells that initiate and conduct impulses.

What is a pacemaker potential?

Unstable resting membrane potential in pacemaker cells.

What causes pacemaker potential depolarization?

Slow Na⁺ influx.

What ion causes rapid depolarization?

Ca²⁺ influx.

What causes repolarization?

K⁺ efflux.

What is the correct sequence of excitation?

SA node → AV node → AV bundle → bundle branches → Purkinje fibers

Total conduction time through heart?

0.22 seconds

Where is the SA node?

Right atrial wall

Function of SA node?

Pacemaker of the heart

Normal firing rate?

~75 bpm (intrinsic ~100 bpm)

Location of AV node?

Inferior interatrial septum

Function of AV node?

Delays impulse (~0.1 sec)

Why delay occurs?

Smaller fibers, fewer gap junctions

AV node intrinsic rate?

50 BPM

Function of AV bundle?

Only electrical connection between atria & ventricles

Function of bundle branches?

Carry impulses to apex

Function of Purkinje fibers?

Distribute impulses through ventricles

Intrinsic ventricular conduction rate?

30 BPM

What is an arrhythmia?

Irregular heart rhythm

What is fibrillation?

Rapid, chaotic contractions

Treatment for fibrillation?

Defibrillation

Sympathetic effect on heart?

Increases rate & force

Parasympathetic effect?

Decreases heart rate

Nerve for parasympathetic control?

Vagus nerve

What ion starts depolarization?

Na⁺ influx

What causes plateau phase?

Ca²⁺ influx

What causes repolarization?

K⁺ efflux

Duration of cardiac AP?

~200 ms

Why is long AP important?

Prevents tetany, ensures pumping

What does an ECG measure?

Electrical activity of heart

What is a P wave?

Atrial depolarization

What is QRS complex?

Ventricular depolarization

What is T wave?

Ventricular repolarization

What is P-R interval?

Atrial → ventricular excitation time

What is S-T segment?

Ventricles fully depolarized

What is Q-T interval?

Ventricular depolarization → repolarization

Enlarged R waves indicate?

Enlarged ventricles

S-T segment elevation/depression indicates?

Ischemia

What is systole?

Contraction phase

What is diastole?

Relaxation phase

What is cardiac cycle?

One complete heartbeat

Relationship of electrical to mechanical events?

Electrical events occur first

What causes “lub”?

AV valves closing

What causes “dup”?

Semilunar valves closing

Formula for cardiac output (CO)?

CO = HR × SV

Normal resting CO?

5.25 L/min

What is stroke volume (SV)?

Blood pumped per beat

Formula for SV?

SV = EDV − ESV

Normal EDV?

120 mL

Normal ESV?

50 mL

Normal SV?

70 mL

What is preload?

Stretch of cardiac muscle before contraction

Main factor affecting preload?

Venous return

Frank-Starling law?

↑ stretch → ↑ contraction → ↑ SV

Positive chronotropic factors?

Increase HR

Negative chronotropic factors?

Decrease HR

What systems regulate HR?

ANS, chemicals, other factors

Hypocalcemia effect?

Depresses heart

Hypercalcemia effect?

↑ HR & contractility

Hyperkalemia effect?

Arrhythmias, cardiac arrest

Hypokalemia effect?

Weak heartbeat, arrhythmias

Who has faster HR: males or females?

Females

Effect of exercise on HR?

Increases HR

Effect of temperature?

↑ temp → ↑ HR

Tachycardia?

HR > 100 bpm

Bradycardia?

HR < 60 bpm

Congestive heart failure (CHF)?

Low CO → inadequate tissue perfusion