Cardiology : Action Potentials

created by Tommymoran on 4 Feb 14, enabled by Lou

Animals

Hard level (46% of success) 30 questions - 1 919 players

Prep for First Cardiology Midterm

What is the correct pathway for the heart's conducting system?

SA Node->AV Node->Atrial Muscle->AV Bundle->Purkjine Fibres->Ventricular Muscle

SA Node->AV Node->AV Bundle->Purkinje Fibres->Atrial Muscle->Ventricular Muscle

SA Node->Atrial Muscle->AV Node->AV Bundle->Ventricular Muscle->Purkinje Fibres

SA Node->Atrial Muscle->AV Node->AV Bundle->Purkinje Fibres-Ventricular Muscle

The Sinoatrial (SA) Node is...

A defined-cluster of conducting-myocytes on the right atrium

A diffuse nodule of myocytes at the Superior Vena Cava-Right Atrium junction

A defined-nodule of specialized-conducting cells at the Inferior Vena Cava-Right Atrium Junction

A diffuse nodule of specialized-conducting cells at the Superior Vena Cava-Right Atrium junction

The following is an action potential representative of what class of cells?

SA Nodal Cells

Myocytes

Nerve Cell

A and C

Which phase in the graph below constitutes the "pacemaker potential? "

Phase 0

Phase 3

Phase 4

None of the above

What is the resting potential of an SA Nodal cell?

-60mV

-70mV

-90mV

None of the above

The action potential in SA Nodal cells is primarily driven by...

Fast Na+ currents

Slow Ca++ currents

Slow K+ currents

None of the above

The slow depolarization apparent in phase 4 is primarily due to. .

The slow L-type Ca++ Channel

A slow, inward Na+ current (funny current)

A slow, outward Na+ current (funny current)

None of the above

What is the function of T-type Ca++ channels?

Open for a long period, resulting in the majority of the cells depolarization in Phase 0

Open transiently in phase 3, to reinstitute calcium stores lost in phase 0

Open for a long period of time in phase 4, to reinstitute calcium stores lost in phase 0

Open transiently, allowing Ca++ influx to further depolarize the cell in phase 4

Funny currents persist...

At all times throughout SA Nodal cell AP propagation

Only when an SA Nodal cell is hyperpolarized

Only during the repolarization of an SA Nodal cell

None of the above.

What primarily causes the repolarization in Phase 3?

A hyperpolarizing outward K+ current

Closing of the L-type Ca++ channels

Opening of the slow acting Na+ channels (funny current)

A and B

What would be one result of hypokalemia in SA nodal cells?

Decreased rate of repolarization, leading to Early AfterDepolarizations (EADs) and arrythmia

Increased rate of repolarization, leading to Early AfterDepolarization (EADs)

Hypoexcitability to due decreased rate of K+ rectifier function

None of the above

What is the intrinsic automaticity of the SA node?

80 beats/minute

100 beats/minute

120 beats/minute

None. The heart cannot beat without outside stimuli.

What type of receptor helps to directly control heart rate?

Cholinergic

ß1-Adrenergic

NMDA

A and B

ß-adrenergic receptors associate with G-proteins. Upon ligand binding, which subunit will bind to and activate adenylyl cyclase?

Alpha-(s)-subunit

ß-subunit

Gamma-subunit

B and C

Activated adenylyl cyclase cleaves ATP in cAMP, resulting in what?

Increased activation of Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels

Earlier L-type Ca++ channel opening

Accelerated Repolarization

All of the above

Cholinergic receptors are associated with a G-protein constituted by the inhibitory alpha-(i)-subunit. Upon decreased cAMP levels, what important kinase activity is deterred?

PKA phosphorylation of adenylyl cyclase

PKB phosphorylation of HCN channels

PKA phosphorylation of L-type Ca++ channels

B and C

What ß-gamma G-protein subunit interaction may counteract the funny current?

Potassium channel interaction

HCN channel interaction

Na+/Ca++ exhcanger interaction

None of the above

What is the function of the AV node?

Limit fibrillation entry into ventricles

Serve as back-up pacemaker

Delay action potential to allow ventricular filling (function as switching-station)

All of the above

Which has the faster intrinsic automaticity (rate of cycle)?

SA Node

AV Node

They are the same

Random filler answer (pick this if you want to be wrong)

What is the function of the delayed action potential in the AV node, compare to that of a Purkinje Fibre, illustrated below?

Separate heart beats to reduce heart stress

Allow for atrial filling

Allow for ventricular filling

There is no function. B is the representation of a pathologic AP

What characteristic of the AV Node and AV bundle result in the slower generation of action potential compared to Purkinje Fibres?

Fewer channels to exchange ions

Generally, smaller and slower ion channels

Denser and less symmetric cellular morphology

A and B

Connexins, intercellular pores, allow the exchange of Na+ ions between cells. What characteristic would you expect of Connexins of the SA and AV nodes compared to Purkinje Fibres?

Smaller diameter

Larger diameter

Slow-conductance

A and C

What allows the ventricles to contract as a syncitium?

Fast conducting NaV1. 5 channels

Fast-acting bundle branches

Purkinje fibre connections

A and C

What ion exchange predominantly drives depolarization in Purkinje Fibres and myocytes?

Na+ influx by NaV1. 5 channels

Ca++ influx by fast-acting Ca++ channels