objective 3 pt 2

Question 1

The intrinsic cardiac conduction system consists of
noncontractile cardiac cells specialized to initiate and
distribute impulses throughout the heart.
Although the heart depolarizes and contracts without
nervous system stimulation, the rhythm can be altered by
autonomic nervous system.

Answer 1

electrical events of the heart

Question 2

what is the sequence of excitation?

Answer 2

Cardiac pacemaker cells pass impulses across heart in ∼0.22 seconds
◦ Coordinates depolarization of the heart
◦ Ensures heart beats as a unit

Question 3

what is the order in which impulses pass across the heart?

Answer 3

1. Sinoatrial (SA) node →
2. Atrioventricular (AV) node →
3. Atrioventricular (AV) bundle →
4. Right and left bundle branches →
5. Sub-endocardial conducting network
   (Purkinje fibers)

Question 4

sets the pace of the heart as it depolarizes faster than
rest of myocardium

Answer 4

pacemaker

Question 5

Located in right atrial wall
◦ Generates impulses about 75×/minute (sinus rhythm)
◦ Innate rate of 100×/minute tempered by extrinsic factors
◦ Impulse spreads across atria, and to AV node

Answer 5

sinoatrial node

Question 6

Located in inferior interatrial septum
◦ Delays impulses approximately 0.1 second
◦ Allows atrial contraction to occur before ventricular contraction
◦ Inherent rate of 50x/minute in absence of SA node input
◦ From the AV node the impulse sweeps to the AV bundle

Answer 6

atrioventricular node

Question 7

Located in superior interventricular septum
◦ Only electrical connection between atria and ventricles
◦ Atria and ventricles not connected via gap junctions
◦ The AV bundle splits into the rt. and lt. bundle branches

Answer 7

antrioventricular bundle

Question 8

Found in interventricular septum
◦ Carry impulses toward apex of heart

Answer 8

right and left bundle branches

Question 9

Extends from interventricular septum into apex and ventricular walls
◦ More elaborate on left side of heart due to size of LV
◦ Process from initiation at SA node to complete contraction takes
~0.22 seconds
◦ Ventricular contraction immediately follows the depolarization wave

Answer 9

sub-endocardial conducting network

Question 10

sends signals
through sympathetic nervous system to
increase both rate and force of contraction
◦ Stimulates SA and AV nodes, heart muscle,
and coronary arteries

Answer 10

cardio-acceleratory center

Question 11

sends
parasympathetic signals via vagus nerve to
decrease heart rate
◦ Inhibits SA and AV nodes via vagus nerves

Answer 11

cardio-inhibitory center

Question 12

is a device that
can detect electrical currents
generated by heart

Answer 12

electrocardiograph

Question 13

is
a graphic recording of electrical
activity
◦ Combination of all action
potentials at given time; not a
tracing of a single AP
◦ Electrodes are placed at various
points on body to measure
voltage differences
◦ 12 lead ECG is most typical

Answer 13

electrocardiogram

Question 14

what are the main features of electrocardiography?

Answer 14

P wave
QRS complex
T wave
P-R interval
S-T segment
Q-T interval

Question 15

depolarization of atria

Answer 15

P wave

Question 16

ventricular depolarization

Answer 16

QRS complex

Question 17

ventricular repolarization

Answer 17

T wave

Question 18

beginning of atrial excitation to beginning of ventricular excitation

Answer 18

P-R interval

Question 19

entire ventricular myocardium depolarization

Answer 19

S-T segment

Question 20

beginning of ventricular depolarization through ventricular repolarization

Answer 20

Q-T interval

Question 21

may be due to enlarged ventricles

Answer 21

enlarged R wave

Question 22

could be cardia ischemia

Answer 22

elevated or depressed ST segment

Question 23

could be repolarization abnormality that increases risk of ventricular arrhythmias

Answer 23

prolonged QT interval

Question 24

period of heart contraction

Answer 24

systole

Question 25

period of heart relaxation

Answer 25

diastole

Question 26

blood flow through heart during one heartbeat Atrial systole and diastole are followed by ventricular systole and diastole ◦ Cycle represents series of pressure and blood volume changes ◦ Mechanical events follow electrical events seen on ECG ◦ Cycle lasts ~ 0.8 secs

Answer 26

cardiac cycle

Question 27

marked by a succession of pressure and blood volume changes in the heart

Answer 27

cardiac cycle

Question 28

what are the phases of the cardiac cycle?

Answer 28

1. Ventricular filling (atrial systole) 2. Isovolumetric contraction 3. Ventricular ejection 4. Isovolumetric relaxation

Question 29

Contraction of atria completes emptying blood out of the atria into the ventricles o AV valves are open; SL valves are closed o Ventricles are relaxed (diastole) and filling with blood o Cycle begins with P wave of ECG o Takes ~ 0.1 sec

Answer 29

atrial systole

Question 30

As the atria relax, the ventricles begin contracting ◦ Begins with QRS complex ◦ AV and SL valves are closed ◦ Pressure increases rapidly but volume remains same ◦ For a split second, the ventricles are completely closed chambers and the blood volume remains constant as the ventricles contract

Answer 30

isovolumetric ventricular contraction

Question 31

Onset coincides with R wave and appearance of 1st heart sound ◦ AV valves closed ◦ SL valves open ◦ Blood forcefully ejected into pulmonary artery and aorta ◦ T wave occurs just before ventricles relax ◦ Residual volume ◦ End-systolic volume ◦ Takes ~ 0.3 secs

Answer 31

ventricular systole

Question 32

SL valves close (2nd heart sound) o AV valves are closed o All chamber relax simultaneously for ~ 0.4 sec o Atria passively fill with blood

Answer 32

isovolumetric ventricular relaxation

Question 33

what are the 2 sounds of the heart?

Answer 33

lub dub

Question 34

first sound is the closing of AV valves at beginning of ventricular systole

Answer 34

Lub

Question 35

second sound is closing of SL valves at beginning of ventricular diastole

Answer 35

Dub

Question 36

the volume of blood pumped by each ventricle in 1 min

Answer 36

cardiac output

Question 37

number of beats per min

Answer 37

HR

Question 38

amount of blood pumped out by one ventricle with each beat

Answer 38

SV

Question 39

factors increase heart rate

Answer 39

positive chronotropic factors

Question 40

factors decrease heart rate

Answer 40

negative chronotropic factors

Question 41

what can HR be regulated by?

Answer 41

autonomic nervous system chemicals other factors

Question 42

can be activated by emotional or physical stressors. upon activation norepinephrine is released

Answer 42

sympathetic nervous system

Question 43

increases HR increased contractility

Answer 43

norepinephrine

Question 44

opposes sympathetic effects. upon activation acetylcholine is released

Answer 44

parasympathetic nervous system

Question 45

slows HR but has little to no effect on contractility

Answer 45

AcH

Question 46

The hormones Epinephrine and Thyroxine influence heart rate. o Epinephrine increases heart rate and contractility o Thyroxine increases heart rate and enhances effects of epinephrine and NE o Intracellular and extracellular ions influence normal heart function

Answer 46

chemical regulation of heart rate

Question 47

fetus has fastest HR; declines with age

Answer 47

age

Question 48

females have faster HR than males

Answer 48

gender

Question 49

increases HR trained athletes can have slow HR

Answer 49

exercise

Question 50

HR increases with increased body temp

Answer 50

body temp