Ap2 Ch 18 Pt 3

Front 1

sequence of excitation

Back 1

– Sinoatrial node 
– Atrioventricular node 
– Atrioventricular bundle 
– Right and left bundle branches 
– Subendocardial conducting network (AKA
Purkinje fibers)

Front 2

Sinoatrial (SA) node

Back 2

–Pacemaker of heart in right atrial wall
• Depolarizes faster than rest of
myocardium

Front 3

(sinus rhythm)

Back 3

–SA node generates impulses about 75X/minute

Front 4

what is the inherent rhthym of the heart?

Back 4

• Inherent rate of 100X/minute tempered
by extrinsic factors

Front 5

Where does the impulse go from the SA node

Back 5

Impulse spreads across atria, & to AV node

Front 6

Atrioventricular (AV) node Where is it?

Back 6

– In inferior interatrial septum

Front 7

–AV node delays impulses approximately 0.1 second. Why?

Back 7

• Because fibers are smaller diameter,
have fewer gap junctions
• Allows atrial contraction prior to
ventricular contraction

Front 8

What is the inherent rate of the AV node?

Back 8

Inherent rate of 50X/minute in absence of
SA node input

Front 9

• Atrioventricular (AV) bundle
(bundle of His)

Back 9

– In superior interventricular septum
–Only electrical connection between atria
and ventricles
• Atria and ventricles not connected via
gap junctions

Front 10

Right and left bundle branches

Back 10

–Two pathways in interventricular septum
–Carry impulses toward apex of heart

Front 11

Subendocardial conducting network
AKA

Back 11

(Purkinje fibers)

Front 12

What do purkinje fibers do?

Back 12

– Complete pathway through interventricular
septum into apex and ventricular walls

Front 13

Where are purkinje fibers more elaborate?

Back 13

– More elaborate on left side of heart

Front 14

How often do AV bundle and purkinje/subendocardial conducting network inherently depolarize?

Back 14

30X/minute in absence of AV node input

Front 15

–Arrhythmias

Back 15

- irregular heart rhythms
–Uncoordinated atrial and ventricular
contractions

Front 16

–Fibrillation

Back 16

- rapid, irregular contractions; useless for pumping blood
 circulation ceases  brain death
• Defibrillation to treat

Front 17

Defective SA node may cause

Back 17

– Ectopic focus or pacemaker

• Extrasystole (premature contraction)

Front 18

Ectopic focus or pacemaker

Back 18

- abnormal pacemaker (cells outside of malfunctioning SA node set rhythm)
– AV node may take over; sets junctional
rhythm (40–60 beats/min); sufficient for blood
circulation

Front 19

Defective AV node may cause

Back 19

–Heart block
• Few (partial) or no (total) impulses
reach ventricles
–Ventricles beat at intrinsic rate –
too slow for life
–Artificial pacemaker to treat

Front 20

Heartbeat modified by:

what increases and decreases?

Back 20

ANS via cardiac
centers in medulla oblongata
–Sympathetic increases rate and force
–Parasympathetic decreases rate

Front 21

–Cardioacceleratory center –

Back 21

sympathetic

– affects SA, AV nodes, heart muscle, coronary arteries

Front 22

–Cardioinhibitory center –

Back 22

parasympathetic

– inhibits SA and AV nodes via vagus nerves

Front 23

Electrocardiogram (ECG or EKG)

Back 23

–Composite of all action potentials
generated by nodal and contractile cells
at given time

Front 24

Three waves:

Back 24

–P wave – depolarization SA node  atria
–QRS complex - ventricular depolarization
and atrial repolarization
–T wave - ventricular repolarization

Front 25

P-R interval

Back 25

– Beginning of atrial excitation to beginning of
ventricular excitation

Front 26

• S-T segment

Back 26

– Entire ventricular myocardium depolarized

Front 27

• Q-T interval

Back 27

– Beginning of ventricular depolarization
through ventricular repolarization

Front 28

Artificial Pacemakers
• Single

Back 28

– left ventricle

Front 29

Artificial Pacemakers

Dual

Back 29

– treat “heart block” – both ventricles

Front 30

Artificial Pacemakers

Biventricular

Back 30

–right atrium & both ventricles

Front 31

Two sounds (lub-dup) associated with
closing of heart valves
1st

2nd

pause

Back 31

– First as AV valves close; beginning of systole
– Second as SL valves close; beginning of
ventricular diastole
– Pause indicates heart relaxation

Front 32

Heart murmurs -

Back 32

abnormal heart sounds; usually indicate
incompetent (fails to close completely) or stenotic valves

Front 33

Mitral valve prolapse:

Back 33

valve disorder affects 1% of population; common in young women genetic basis resulting in abnormal chordae tendineae or a malfunction of the papillary muscles