CV3 Cardiac conduction system

Question 1

what is the cardiac conduction system

Answer 1

network of nodes, cells and signals
controls heartbeat
inherent & rhythmical electrical activity (heart creates its impulses)
makes the heart an effective pump

Question 2

what are autorhythmic cells

Answer 2

network of specialised cardiac muscle fibres
generate spontaneous action potentials

nerve impulses from ANS and endocrine hormones modify the heartbeat
does not establish the fundamental rhythm

Question 3

what’s involved in specialised cardiac muscle fibres

Answer 3

in SA node, AV node & Purkinjean fibres
self-excitable
pacemaker activity

Question 4

can a heart still beat with the nerves cut?

Answer 4

a living heart removed from the body will continue to beat despite cutting nerves

Question 5

from top to bottom which order do the nerve fibres go
Purkinje fibres
Atrioventricular (AV) bundle (bundle of his)
Atrioventricular (AV) node
Sinoatrial (SA) node
Right and left bundle branches

Answer 5

1. sinoatrial (SA) node
2. atrioventricular (AV) node
3. atrioventricular (AV) bundle (bundle of his)
4. right and left bundle branches
5. Purkinje fibres

Question 6

what are the three steps in ventricular action potential

Answer 6

1. Rapid Depolarisation
2. Plateau
3. Repolarisation

Question 7

what happens during Rapid Depolarisation

Answer 7

as Na+ enters

Question 8

what happens during Plateau

Answer 8

maintained depolarisation; some K+ leaves
slows Ca2+ enters
binds to troponin
actin + myosin slide

Question 9

what happens during Repolarisation

Answer 9

as K+ exits, & Ca2+ leaves

Question 10

what is a electrocardiogram (ECG)

Answer 10

recording of electrical changes that accompany AP propagation that can be detected at the surface of the body

Question 11

where would you place the ECG

Answer 11

place electrodes on 4 limbs & 6 positions on the chest

Question 12

what are the 3 recognisable waves accompany each heartbeat

Answer 12

P wave
QRS complex
T wave

Question 13

what is the P wave

Answer 13

atrial depolarisation
(contraction)

Question 14

what is the QRS complex

Answer 14

onset of ventricular depolarisation
(contraction)

Question 15

what is the T wave

Answer 15

ventricular repolarisation
(just before ventricles start to relax)

Question 16

if P wave is the larger wave?

Answer 16

enlarged atrium

Question 17

in QRS if Q is enlarged

Answer 17

MI

Question 18

in QRS if R is enlarged

Answer 18

enlarged ventricles

Question 19

if T is flatter

Answer 19

insufficient O2
coronary artery disease

Question 20

if there’s a interval between P-Q

Answer 20

scar tissue
coronary artery disease
rheumatic fever

Question 21

if the S-T segment is elevated

Answer 21

acute MI
depressed- insufficient O2

Question 22

if the Q-T interval lengthens

Answer 22

myocardial damage or coronary ischaemia
conduction abnormalities

Question 23

what is the healthy adult pulse at rest

Answer 23

average 75bpm
(60-100)

Question 24

what is the healthy adult pulse at sleep

Answer 24

40 bpm

Question 25

what is the healthy adult pulse with strenuous exercise

Answer 25

200-220 bpm

Question 26

what are the modification of heartbeats

Answer 26

hormones & neurotransmitters
ectopic pacemakers

Question 27

what does the hormones & neurotransmitters do?

Answer 27

speed or slow pacing of heart by SA node fibres

Question 28

what does the Ectopic pacemaker do

Answer 28

out with SA node
develops abnormal excitability
(can produce extra beats or abnormally paced heart)
can be triggered by stimulants
(nicotine, caffeine)