Midterm 1 - Cardiac Function and Control

Question 1

what are the 2 types of muscle cells that compose the myocardium

Answer 1

contractile cells
auto rhythmic cells

Question 2

what percentage of cells in myocardium physically contract

Answer 2

99%

Question 3

what is require for contraction

Answer 3

action potential

Question 4

what are autorhythmic cells

Answer 4

modified non-contractile cells

Question 5

where are autorhytmic cells

Answer 5

concentrated in specific regions of the heart

Question 6

what do autorhytmic cells do

Answer 6

spontaneously generate action potential - pacemaker

Question 7

what are gap junctions

Answer 7

water-filled pores that form open connections between adjacent cells

Question 8

what do gap junctions allow

Answer 8

for ion to move freely from one cell to another - electrical activity can pass from cell to cell

Question 9

what do the gap junctions have no need for

Answer 9

no need for synapse - allow AP to jump rapidly through cells

Question 10

what is the electrical conduction system generated by

Answer 10

pacemaker cells - auto rhythmic

Question 11

what is the Sino-Atrial (SA) node

Answer 11

the command centre (determine heart contraction)

Question 12

what does the SA node do

Answer 12

rhythmical self excitation

Question 13

what is the difference between SA and AV nodes

Answer 13

AV nodes have slower pace, therefore under SA control

Question 14

do both AV and SA nodes have auto rhythmic activity

Answer 14

yes

Question 15

what is AV node a gateway for

Answer 15

electrical conduction between atria and ventricle

Question 16

what does the bundle of His and Purkinje fibers help

Answer 16

to quickly propagate electrical activity from the AV node to the rest of the ventricles

Question 17

what is the role of the electrical system

Answer 17

maintain appropriate heart rate
coordinate contraction of atria and ventricles
coordinate contraction of each chamber

Question 18

what is the clinical relevance of the electrical system

Answer 18

use ECG to determine heart rhythm
problems with conduction - abnormal rhythm (arrhythmia)

Question 19

during contraction, where do APs from auto rhythmic cells propagate to

Answer 19

the contractile cells

Question 20

what is responsible for muscle contraction

Answer 20

action potentials in contractile cells

Question 21

due to the gap junction, what can the heart be considered

Answer 21

a functional syncytium

Question 22

do to the gap junction, what rule does contraction follow

Answer 22

all or none rule

Question 23

how does the action potential of contractile cells differ from auto rhythmic

Answer 23

stable resting membrane potential (no drift)

Question 24

how does the action potential of contractile cells differ from skeletal muscle AP

Answer 24

duration
length of refractory period

Question 25

duration of skeletal muscle AP

Answer 25

very short, milliseconds

Question 26

duration of contractile muscle AP

Answer 26

long, 100s of milliseconds

Question 27

does skeletal muscle have a shorter or longer refractory period than cardiac muscle

Answer 27

shorter

Question 28

what is the effect of the sympathetic nervous system

Answer 28

stimulates heart rate increases contractile force reduces the contraction time

Question 29

how does the SNS stimulate the heart rate

Answer 29

stimulates the firing of the SA node and the velocity of the AV node conduction (shorter delay)

Question 30

how does the SNS increase contraction force

Answer 30

increase release of Ca2+ from sarcoplasmic store, which increases strength

Question 31

how does the SNS reduce contraction time

Answer 31

increases speed of Ca2+ transport (reduces plateau length)

Question 32

what is present in all cardiac cells associated with SNS

Answer 32

actions mediated by epinephrine/norepinephrine on B-adrenegic receptors

Question 33

effect of the parasympathetic nervous system (vagus nerve)

Answer 33

decreases heart rate

Question 34

how does the PSNS decrease heart rate

Answer 34

reduce SA node firing and decreases the velocity of the AV node conduction (longer delay)

Question 35

what occurs in auto rhythmic cells due to PSNS

Answer 35

actions mediated by binding of acetylcholine on muscarinic receptors - increase in K+ permeability and hyper polarization increase time required to reach the AP threshold

Question 36

where is the current conducted from heart cells firing AP simultaneously

Answer 36

through body fluid to skin

Question 37

what does an ECG do

Answer 37

measure heart membrane potential throughout cardiac cycle

Question 38

what do electrodes do in ECG

Answer 38

they are placed at different location on skin to read progression of the electric current wave

Question 39

how many waves does a standard ECG have

Answer 39

3

Question 40

what are the 3 waves of an ECG

Answer 40

P wave QRS wave T wave

Question 41

what does the P wave on an ECG show

Answer 41

depolarization of atria

Question 42

what does the QRS wave show on ECG

Answer 42

depolarization of the ventricles

Question 43

what does the T wave on an ECG show

Answer 43

depolarization of the ventricles

Question 44

what is the base-apex lead configuration

Answer 44

one lead on left chest, second lead over the neck in jugular groove

Question 45

what does the shape of an ECG depend on

Answer 45

where electrodes are placed

Question 46

2 uses of an ECG

Answer 46

assessment of heart rate and rhythm detection of abnormalities

Question 47

how does an ECG measure heart rate

Answer 47

measure intervals between cycles

Question 48

how does an ECG measure contraction force

Answer 48

measure amplitude of waves

Question 49

how does an ECG measure rhythm

Answer 49

measure intervals between each waves

Question 50

how does an ECG detect abnormalities

Answer 50

by measuring heart rate under resting conditions rhythm

Question 51

what is bradycardia

Answer 51

slower rate

Question 52

what is tachycardia

Answer 52

faster rate

Question 53

what are problems with rate generally associated with

Answer 53

the SA node... pacemaker is an artificial SA node

Question 54

how does an ECG detect rhythm

Answer 54

abnorally long P-Q interval ectopic beats (extrasystole)

Question 55

what does an abnormally long P-Q interval mean

Answer 55

AV conduction problem

Question 56

what do ectopic beats (extrasystole) mean

Answer 56

action potential generated independently of the SA node which results in ventricular extracontraction