A normal heartbeat is initiated in the:

A. SA node
B. AV node
C. AV bundle
D. Purkinje fibers

A. SA node

After originating in the sinus node, the impulse next normally travels to the:

A. bundle branches
B. Purkinje network
C. AV node
D. ventricular myocardium

C. AV node

At the AV node, impulses are normally:

A. accelerated
B. delayed
C. blocked
D. amplified

B. delayed

The AV bundle normally conducts impulses from the:

A. ventricles to atria
B. SA node to atria
C. Purkinje fibers to apex
D. atria into ventricles

D. atria into ventricles

The right and left bundle branches ultimately distribute impulses to:

A. both atria
B. all ventricular regions
C. the AV valves
D. the sinus node

B. all ventricular regions

The sinus node is located in the:

A. superior posterolateral right atrium
B. inferior left atrial wall
C. interventricular septum
D. coronary sinus opening

A. superior posterolateral right atrium

Relative to the superior vena cava opening, the sinus node lies:

A. medial and above
B. anterior and below
C. posterior and medial
D. below and lateral

D. below and lateral

Sinus nodal fibers connect directly to atrial muscle fibers so that:

A. ventricular filling begins sooner
B. AV delay becomes longer
C. atrial depolarization spreads immediately
D. semilunar valves open earlier

C. atrial depolarization spreads immediately

Some cardiac fibers can spontaneously depolarize, producing rhythmic discharge. This property is called:

A. self-excitation
B. conduction delay
C. summation
D. tetany

A. self-excitation

The resting membrane potential of sinus nodal fibers is normally closest to:

A. -90 to -95 mV
B. -55 to -60 mV
C. -40 to -45 mV
D. +20 to +15 mV

B. -55 to -60 mV

Sinus nodal cells are less negative than ventricular cells mainly because they are naturally leaky to:

A. potassium and chloride
B. calcium and potassium
C. sodium and potassium
D. sodium and calcium

D. sodium and calcium

Which list correctly names the three main cardiac ion channels?

A. chloride, sodium, magnesium
B. calcium, chloride, funny
C. fast sodium, L-type calcium, potassium
D. sodium-potassium pump, chloride, calcium

C. fast sodium, L-type calcium, potassium

Because the sinus node membrane potential is less negative, which channels remain closed during nodal action potential generation?

A. potassium channels
B. fast sodium channels
C. chloride channels
D. ryanodine channels

B. fast sodium channels

The sinus nodal action potential upstroke is slower than ventricular muscle because nodal cells rely mainly on:

A. slow sodium-calcium channels
B. fast sodium channels
C. inward rectifier potassium
D. chloride influx

A. slow sodium-calcium channels

Between heartbeats, the slow rise in sinus nodal resting membrane potential is caused mainly by:

A. potassium leaving the cell
B. calcium sequestration into SR
C. sodium influx
D. chloride influx

C. sodium influx

When sinus nodal membrane potential reaches threshold, about _____, L-type calcium channels open.

A. -90 mV
B. -60 mV
C. 0 mV
D. -40 mV

D. -40 mV

The self-excitation of sinus nodal fibers is due primarily to their

A. inherent leakiness
B. prolonged refractory period
C. high contractile force
D. dense fast sodium current

A. inherent leakiness

To avoid remaining continuously depolarized, sinus nodal fibers do which of the following?

A. open fast sodium channels, lose potassium
B. inactivate calcium channels, lose potassium
C. close potassium leak channels, lose potassium
D. activate chloride influx, lose potassium

B. inactivate calcium channels, lose potassium

Which additional event helps terminate the sinus nodal action potential and prevent persistent depolarization?

A. sodium retention in cell
B. calcium influx acceleration
C. chloride entry
D. potassium diffusion outward

D. potassium diffusion outward

Excess negativity developing inside the fiber after repolarization is called:

A. depolarization
B. afterdepolarization
C. hyperpolarization
D. automaticity

C. hyperpolarization

Which sequence best describes the sinus node action-potential process?

A. Self-excitation, recovery, hyperpolarization, threshold drift, re-excitation
B. Recovery, depolarization, threshold drift, hyperpolarization, re-excitation
C. Hyperpolarization, recovery, self-excitation, threshold drift, re-excitation
D. Threshold drift, self-excitation, recovery, re-excitation, hyperpolarization

A. Self-excitation, recovery, hyperpolarization, threshold drift, re-excitation

Rapid activation of the left atrium after sinus node discharge is aided most directly by the:

A. middle internodal tract
B. posterior internodal tract
C. AV bundle
D. anterior interatrial band

D. anterior interatrial band

Which tracts conduct impulses from the SA node to the AV node?

A. anterior, lateral, septal pathways
B. anterior, middle, posterior internodal pathways
C. left, right, posterior bundle branches
D. Bachmann, Purkinje, nodal tracts

B. anterior, middle, posterior internodal pathways

Which structure primarily delays transmission before impulses enter the ventricles?

A. SA node
B. AV bundle
C. AV node
D. Purkinje fibers

C. AV node

During EP mapping, a conduction structure is identified in the posterior wall of the right atrium behind the tricuspid valve. This is the:

A. AV node
B. SA node
C. coronary sinus
D. bundle branch

A. AV node

The total delay in the AV node plus AV bundle is closest to:

A. 0.03 seconds
B. 0.16 seconds
C. 0.13 seconds
D. 0.30 seconds

C. 0.13 seconds

The conduction delay between the sinus node and AV node is approximately:

A. 0.13 seconds
B. 0.10 seconds
C. 0.16 seconds
D. 0.03 seconds

D. 0.03 seconds

The total delay before the excitatory signal reaches contracting ventricular muscle is about:

A. 0.13 seconds
B. 0.16 seconds
C. 0.03 seconds
D. 0.30 seconds

B. 0.16 seconds

Slow conduction through nodal tissue occurs mainly because of diminished numbers of:

A. gap junctions
B. sodium channels
C. myofibrils
D. T tubules

A. gap junctions

Which fibers continue from the AV node through the AV bundle into the ventricles?

A. atrial conducting fibers
B. internodal bands
C. papillary fibers
D. special Purkinje fibers

D. special Purkinje fibers

Purkinje fibers are best described as:

A. small fibers, rapid contraction
B. nonconducting myocardial cords
C. large fibers, fast conduction
D. thin fibers, slow conduction

C. large fibers, fast conduction

The conduction velocity in Purkinje fibers is closest to:

A. 0.3 to 0.5 m/sec
B. 1.5 to 4.0 m/sec
C. 4.5 to 6.0 m/sec
D. 0.03 to 0.13 m/sec

B. 1.5 to 4.0 m/sec

Rapid Purkinje transmission is attributed mainly to the very high permeability of:

A. gap junctions at discs
B. L-type calcium channels
C. fast sodium channels
D. potassium leak pores

A. gap junctions at discs

Purkinje fibers contract very little during impulse transmission because they contain few:

A. intercalated discs
B. mitochondria
C. T tubules
D. myofibrils

D. myofibrils

Which statement is a special characteristic of the AV bundle?

A. It conducts only retrograde impulses
B. It lies within atrial free wall
C. Impulses normally cannot travel backward
D. It is the main pacemaker

C. Impulses normally cannot travel backward

The only site where atrial muscle is not separated from ventricular muscle is the:

A. AV node
B. AV bundle
C. Purkinje network
D. SA node

B. AV bundle

The continuous fibrous barrier between atrial and ventricular muscle normally acts as an:

A. insulator
B. amplifier
C. pacemaker
D. depolarizer

A. insulator

The left and right bundle branches travel primarily:

A. upward toward the base
B. laterally into the atria
C. downward toward the apex
D. posteriorly to the vena cava

C. downward toward the apex

The terminal Purkinje fibers penetrate into the ventricular muscle mass approximately:

A. halfway through myocardium
B. to the epicardium only
C. through the full thickness
D. one-third of the way

D. one-third of the way

A lesion affecting the fibrous insulating barrier but sparing the AV bundle would most likely alter which normal property of the heart?

A. Purkinje automaticity
B. electrical separation of atria and ventricles
C. atrial depolarization by SA node
D. ventricular repolarization pattern

B. electrical separation of atria and ventricles

The gross arrangement of cardiac muscle around the heart is best described as a:

A. double spiral
B. circumferential ring
C. radial lattice
D. single helix

A. double spiral

Between the spiraling layers of cardiac muscle lie:

A. Purkinje sheets
B. elastic laminae
C. AV nodal bands
D. fibrous septa

D. fibrous septa

The total time for impulse transmission from the bundle branches to the last ventricular muscle fibers is closest to:

A. 0.16 seconds
B. 0.03 seconds
C. 0.06 seconds
D. 0.13 seconds

C. 0.06 seconds

If isolated from faster pacemakers, AV nodal fibers typically discharge at an intrinsic rate of:

A. 15-40/min
B. 40-60/min
C. 70-80/min
D. 100-120/min

B. 40-60/min

Purkinje fibers, when acting as an intrinsic pacemaker, usually discharge at:

A. 15-40/min
B. 40-60/min
C. 70-80/min
D. 90-110/min

A. 15-40/min

The normal discharge rate of the sinus node is about:

A. 15-40/min
B. 40-60/min
C. 70-80/min
D. 90-100/min

C. 70-80/min

The SA node normally controls cardiac rhythmicity primarily because it has the:

A. longest refractory period
B. highest discharge rate
C. greatest contractile force
D. slowest conduction velocity

B. highest discharge rate

A pacemaker located anywhere other than the sinus node is called an:

A. escape focus
B. reentry circuit
C. ectopic pacemaker
D. nodal bypass tract

C. ectopic pacemaker

Blockage of cardiac impulse transmission can cause a:

A. shift of pacemaker
B. stronger SA discharge
C. shorter refractory period
D. loss of ventricular systole

A. shift of pacemaker

AV block refers to failure of the cardiac impulse to pass from the:

A. ventricles to atria
B. bundle branches to Purkinje
C. atria to ventricles
D. SA node to atria

C. atria to ventricles

In complete AV block, which chambers continue to beat at their own normal rhythm?

A. ventricles
B. atria
C. both equally
D. neither chamber

B. atria

In AV block, the structure that usually becomes the pacemaker for the ventricles is the:

A. SA node
B. atrial muscle
C. AV bundle only
D. Purkinje system

D. Purkinje system

A patient with complete AV block briefly has no effective ventricular rhythm before a slow escape rhythm appears. This delay occurs because the Purkinje fibers are initially:

A. overstimulated
B. depolarized maximally
C. in a suppressed state
D. blocked by acetylcholine

C. in a suppressed state

In Stokes-Adams syndrome, the Purkinje system may fail to begin firing for approximately:

A. 1-2 seconds
B. 5-20 seconds
C. 20-40 seconds
D. 40-60 seconds

B. 5-20 seconds

A patient with sudden complete AV block loses consciousness after a few seconds because cerebral blood flow ceases. Syncope usually occurs after about:

A. 1-2 seconds
B. 8-10 seconds
C. 12-15 seconds
D. 4-5 seconds

D. 4-5 seconds

The delayed pickup of ventricular beating after AV block is called:

A. ventricular fibrillation
B. Wenckebach phenomenon
C. Stokes-Adams syndrome
D. pulsus alternans

C. Stokes-Adams syndrome

Parasympathetic fibers to the heart are distributed mainly to the:

A. SA and AV nodes
B. ventricular free walls
C. bundle branches
D. Purkinje network

A. SA and AV nodes

Sympathetic fibers are distributed to:

A. only the atria
B. all parts of heart
C. only SA node
D. only ventricles

B. all parts of heart

The main neurotransmitter mediating parasympathetic control of the heart is:

A. epinephrine
B. dopamine
C. acetylcholine
D. serotonin

C. acetylcholine

Parasympathetic stimulation has two major cardiac effects: decreased SA nodal rate and decreased excitability of the:

A. Purkinje fibers
B. ventricular myocardium
C. bundle branches
D. AV junctional fibers

D. AV junctional fibers

Ventricular escape refers to the ability of the Purkinje fibers to:

A. block atrial conduction
B. pace ventricles independently
C. increase SA discharge
D. shorten AV delay

B. pace ventricles independently

Acetylcholine released from vagal nerves greatly increases membrane permeability to:

A. sodium ions
B. calcium ions
C. chloride ions
D. potassium ions

D. potassium ions

Sympathetic stimulation of the heart causes increased SA discharge, increased conduction, and increased:

A. force of contraction
B. vagal tone
C. potassium efflux
D. AV nodal delay

A. force of contraction

Stimulation of sympathetic cardiac nerves releases:

A. epinephrine
B. acetylcholine
C. norepinephrine
D. dopamine

C. norepinephrine

Norepinephrine exerts its main cardiac effects through:

A. alpha-1 receptors
B. muscarinic receptors
C. beta-2 receptors
D. beta-1 receptors

D. beta-1 receptors

Sympathetic stimulation increases membrane permeability primarily to:

A. potassium and chloride
B. sodium and calcium
C. calcium and chloride
D. sodium and potassium

B. sodium and calcium