Electrical Wiring of Heart

What is functional syncytium?

all cells depolarize and contract at same time

What are intercalated disks?

connections between heart cells that contribute to functional syncytium

What are intercalated disks connected by?

gap junctions (allow ions to pass) and desmosomes (hold cells together)

What is the conduction system?

electrical wiring of the heart

What does the conduction system ensure?

coordinated contraction; generate action potentials and conduct action potentials to other heart cells via gap junctions

What are the 2 modified muscle cells?

pacemaker cells and autorhythmic

Where does the conduction system start?

at the superior wall of the right atrium

What structures does the conduction system consist of?

SA node, AV node, AV bundle, R and L bundle branches, purkinje fibers

Explain the function of the sinoatrial node?

part of conduction system; primary pacemaker; generates electrical impulse spreading to atria to contract

What is the function of the atrioventricular node?

part of conduction system; secondary pacemaker; spread from atria to ventricle to fill with blood

What is the function of the AV bundle?

part of conduction system; splits into left and right branches; carries signal from ventricles to both sides of the heart

What is the function of purkinje fibers?

part of the conduction system; extend from branches throughout ventricles; even impulses for ventricles to contract bottom up

What are pacemaker potentials?

conductile slow, spontaneous depolarization between heartbeat

What are pacemaker potentials triggered by?

hyper-polarization in conductile muscle cells

What happens in the cell during a pacemaker potential, depolarization phase, and repolarization phase?

Pacemaker:

1. Voltage gated K+ channels close, F-type Na+ channels open

2. T-type voltage-gated Ca2+ channels open

Depolarization:

1. L-type voltage-gated Ca2+ channels open - triggers AP at -40mV

Repolarization:

1. voltage-gated Ca2+ channels close; voltage-gated K+ channels open

How does epinephrine and noepinephrine modulate pacemaker potentials?

increase production of cAMP = keeps cardiac pacemaker channels open

Whats another name for pacemaker channels?

HCN channels

How does the parasympathetic nervous system slow heart rate?

in pacemaker potentials; parasympathetic neurons secrete AcH to opens K+ channels

What is a contractile cell?

contracts to generate force and pump blood in heart

Whats the difference between a conductile and contractile cell?

conductile - spreads electrical signals through heart to coordinate heartbeat

contractile - contracts to pump blood

Can contractile cells reach threshold without conductile cells?

Nope