origin + conduction of cardiac impulse

Question 1

what is the heart

Answer 1

electrically controlled muscular pump which sucks and pumps blood

Question 2

where are electrical signals which control the heart generated

Answer 2

within the heart

Question 3

the heart is capable of beating rhythmically in the absence of external stimuli (T/F)

Answer 3

True

Question 4

what is autorhythmicity

Answer 4

heart is capable of beating rhythmically in the absence of external stimuli

Question 5

excitation originates

Answer 5

pacemaker cells in sino-atrial node

Question 6

what initiates heart beat

Answer 6

cluster of specialised pacemaker cell in SA node

Question 7

where is the SA node located

Answer 7

Upper right atrium

Question 8

SA node does not drive entire heart (T/F)

Answer 8

False - does drive entire heart

Question 9

What is sinus rhythm?

Answer 9

Heart controlled by sino-atrial node

Question 10

How does cardiac excitation originate?

Answer 10

• cells in SA node = no stable resting membrane potential
• cells in SA node = generate regular spontaneous pacemaker potentials
• spontaneous membrane potential takes membrane potential to threshold
• every time threshold reached = action potential
• –> regular spontaneous action potentials in SA node

Question 11

define pacemaker potential

Answer 11

slow depolarisation of membrane potential to a threshold

Question 12

pacemaker potential due to

Answer 12

• decrease in K+ efflux
• Na+ and K+ influx
• transient Ca++ influx

Question 13

explain rising phase of action potential

Answer 13

• depolarisation
• activation of long lasting L-type Ca++ channels
• Ca++ influx

Question 14

explain falling phase of action potential

Answer 14

• repolarisation
• activation of K+ channels
• K+ efflux

Question 15

Cell-to-cell current flow moves via

Answer 15

Gap junctions

Question 16

Give characteristics of the AV node

Answer 16

• small bundle of specialised cells
• located at base of right atrium just above junction of atria and ventricles
• only point of electrical contact between A + V
• smal in diameter
• slow conduction velocity

Question 17

Spread of Excitiation

Answer 17

-across atria = cell-to-cell conduction via gap junctions
-SA to AV node = cell-to-cell conduction via gap junctions
AV node = conduction delayed (atrial systole to proceed ventricular diastole
-Bundle of His, Purkinjie Fibres = rapid spread of action potentials to ventricles
-ventricular muscle = cell-to-cell conduction

Question 18

Phase 0 of ventricular muscle action potential

Answer 18

fast Na+ influx

Question 19

Phase 1 of ventricular muscle action potential

Answer 19

closure of Na+ channels

transient K+ efflux

Question 20

Phase 2 of ventricular muscle action potential

Answer 20

mainly Ca++ influx

AKA plateau phase

Question 21

Phase 3 of ventricular muscle action potential

Answer 21

Closure of Ca++ channels and K+ efflux

Question 22

Phase 4 of ventricular muscle action potential

Answer 22

Resting membrane potential

Question 23

sympathetic stimulation

Answer 23

increases HR

Question 24

parasympathetic stimulation

Answer 24

decreases HR

Question 25

Heart rate is mainly controlled by what system?

Answer 25

Autonomic nervous system

Question 26

Explain vagus nerve

Answer 26

- parasympathetic supply to heart | - continuous influence on SA under normal resting conditions

Question 27

Explain vagus tone

Answer 27

- dominates under normal resting conditions - slows intrinsic heart rate - 100 to 70bpm

Question 28

Normal resting heart rate values

Answer 28

60-100 bpm

Question 29

Resting heart rate less than 60bpm =

Answer 29

bradycardia

Question 30

resting heart rate more than 100bpm =

Answer 30

tachycardia

Question 31

what does vagus nerve supply?

Answer 31

SA and AV node

Question 32

Vagal stimulation

Answer 32

slows HR | increases AV nodal delay

Question 33

what is the neurotransmitter in parasympathetic supply of the heart

Answer 33

acetyl choline acting through muscarinic M2 receptors

Question 34

what is atropine

Answer 34

-competitive inhibitor of acetylcholine

Question 35

when is atropine used

Answer 35

extreme bradycardia (speeds up the heart)

Question 36

outline the effects of vagal stimulation on pacemaker potentias

Answer 36

- cell hyperpoalrises - longer to reach threshold - slope of pacemaker potential decreases - frequency of AP decreases - negative chronotropic effect

Question 37

what does cardiac sympathetic nerves supply?

Answer 37

SA node AV node Myocardium

Question 38

what does sympathetic stimulation do

Answer 38

- increase HR - decrease AV nodal delay - increases contraction force

Question 39

what is the sympathetic supply of the heart neurotransmitter

Answer 39

noradrenaline acting through B1 adrenoreceptos

Question 40

noradrenaline effect on pacemaker cells

Answer 40

- pacemaker potential slope increases - pacemaker potential reaches threshold quicker - frequency of action potentials increases (positive chrronotropic effect)

Question 41

what is an ECG?

Answer 41

record of depolarisation and repolarisation cycle of cardiac muscle obtained from skin surface

Question 42

P wave

Answer 42

Atrial depolarisation

Question 43

QRS Complex

Answer 43

Ventricular depolarisation

Question 44

T wave

Answer 44

Ventricular depolarisation

Question 45

PR interval

Answer 45

Largely AV node delay

Question 46

ST segment

Answer 46

Ventricular systo;e

Question 47

TP interval

Answer 47

Diastole