Physiology 1

Question 1

What is the heart?

Answer 1

An electrically controlled muscular pump

Question 2

Where are the electrical signals that control the heart generated?

Answer 2

Within the heart itself

Question 3

What is autorhythmicity?

Answer 3

Heart capable of beating rhythmically in absence of external stimuli

Question 4

Where in the heart does excitation normally originate?

Answer 4

Pacemaker cells in sino-atrial node

Question 5

What in the heart initiates the heart beat?

Answer 5

Pacemaker cells in sino-atrial node

Question 6

Where is SA node located?

Answer 6

Upper right atrium

Question 7

What is the function of the SA node?

Answer 7

Sets pace for entire heart

Question 8

What is a heart controlled by SA node said to be?

Answer 8

In sinus rhythm

Question 9

How does cardiac excitation normally originate?

Answer 9

* Cells in SA node do not have stable resting membrane potential
* Exhibit spontaneous pacemaker potential
* Spontaneous pacemaker potential take membrane potential above threshold to generate an action potential

Question 10

What is the pacemaker potential?

Answer 10

Slow depolarisation of membrane potential to threshold

Question 11

What is the ionic basis for spontaneous pacemaker potential? (3)

Answer 11

* Decrease in K+ efflux
* Na+ and K+ influx (funny current)
* Transient Ca++ influx

Question 12

What channel type causes transient Ca++ influx?

Answer 12

T-type Ca++ channels

Question 13

What is the ionic basis for pacemaker action potential?

Answer 13

Once threshold is reached:
* Depolarisation caused by activation of long lasting L-type Ca++ channels
* Results in Ca++ influx

Question 14

What is repolarisation caused by? (2)

Answer 14

* Inactivation of L-type Ca++ channels
* Activation of K+ channels causing K efflux

Question 15

Understand diagram

Answer 15

…

Question 16

How does cardiac excitation normally spread across the heart?

Answer 16

Question 17

What allows the cell-to-cell current flow in the heart?

Answer 17

Gap junctions

Question 18

What exists between cardiac myocytes?

Answer 18

Intercalated disc

Question 19

What is the atrioventricular node?

Answer 19

Small bundle of specialised cardiac cells

Question 20

Where is AV node located?

Answer 20

Base of right atrium

Question 21

What is the only point of electrical contact between atria and ventricles?

Answer 21

AV node

Question 22

Why is conduction delayed in AV node?

Answer 22

To allow atrial systole to precede ventricular systole

Question 23

What is the function of the Bundle of His and Purkinje fibres?

Answer 23

Allow rapid spread of action potential to ventricles

Question 24

How does AP spread through ventricular muscle?

Answer 24

Cell-to-cell conduction via gap junctions

Question 25

Is the action potential in cardiac muscle cells the same as the action potential is pacemaker cells?

Answer 25

No, different

Question 26

Do cardiac myocytes have an unstable resting potential like pacemaker cells?

Answer 26

No, resting membrane potential remains at -90 mV until cell is excited

Question 27

What is phase 0 of action potential in atrial and ventricular myocytes?

Answer 27

Fast Na+ influx reverses membrane potential to +20 mV (depolarisation) (NOT calcium influx like in pacemaker cells)

Question 28

What is phase 1, 2, 3 and 4 of action potential in atrial and ventricular myocytes?

Answer 28

\* Phase 1 - closure of Na+ channels and transient K+ efflux \* Phase 2 - mainly Ca++ influx \* Phase 3 - repolarisation, closure of Ca++ channels and K+ efflux \* Phase 4 - resting membrane potential

Question 29

What is plateau phase of action potential?

Answer 29

Unique to cardiac muscle cells - membrane potential is maintained near the peak of action potential for a few hundred milliseconds

Question 30

What causes plateau phase of action potential?

Answer 30

Influx of Ca++ through L-type Ca++ channels (phase 2)

Question 31

What causes repolarisation in cardiac muscle action potential?

Answer 31

Inactivation of Ca++ channels and activation of K+ channels resulting in K+ efflux

Question 32

What is heart rate mainly influenced by?

Answer 32

Autonomic NS

Question 33

What is the effect of sympathetic stimulation of the heart?

Answer 33

Increases HR

Question 34

What is the effect of parasympathetic stimulation of the heart?

Answer 34

Decreases HR

Question 35

Explain autonomic NS influence on normal resting heart rate

Answer 35

\* Vagus nerve (parasympathetic) exerts continuous influence on SA node under resting conditions \* Vagal tone dominates under resting conditions \* Vagal tone slows intrinsic HR from 100 ppm to a normal resting HR of 70 ppm

Question 36

Which group of people tend to have increased vagal tone?

Answer 36

Athletes

Question 37

What is normal resting heart rate?

Answer 37

60 - 100 bpm

Question 38

What is a resting heart rate less than 60? More than 100?

Answer 38

``` \<60 = bradycardia \>100 = tachycardia ```

Question 39

What does vagus nerve supply in the heart?

Answer 39

SA and AV node

Question 40

What is the effect of vagal stimulation of the heart? (2)

Answer 40

\* Slows heart rate \* Increases AV nodal delay

Question 41

What neurotransmitter is responsible for vagal parasympathetic stimulation of the heart?

Answer 41

Acetylcholine acting on muscarinic M2 receptors

Question 42

What drug is given to patients with extreme bradycardia to speed up the heart?

Answer 42

Atropine - a competitive inhibitor of acetylcholine

Question 43

What is the effect of vagal stimulation on pacemaker potentials? (4)

Answer 43

\* Cell hyperpolarises \* Takes longer to reach threshold \* Slope of pacemaker potential decreases \* Frequency of AP decreases

Question 44

What is the effect of vagal stimulation on pacemaker potentials, or anything that slows down heart rate known as?

Answer 44

Negative chronotropic effect

Question 45

What do cardiac sympathetic nerves supply?

Answer 45

SA, AV node and myocardium

Question 46

What is the effect of sympathetic stimulation on the heart?

Answer 46

\* Increases HR \* Decreases AV nodal delay \* Increases force of contraction

Question 47

What neurotransmitter is responsible for sympathetic stimulation of the heart?

Answer 47

Noradrenaline acting through B1 adrenoceptors

Question 48

What is the effect of noradrenaline on pacemaker cells? (3)

Answer 48

\* Slope of pacemaker potential increases \* Pacemaker potential reaches threshold quicker \* Frequency of action potential increases

Question 49

What is the effect of noradrenaline on pacemaker potentials, or anything that speeds up heart rate known as?

Answer 49

Positive chronotropic effect

Question 50

What is an ECG?

Answer 50

Depolarisation and repolarisation cycle of cardiac muscle obtained from skin surface

Question 51

What are standard limb leads of ECG? (3)

Answer 51

\* Lead I: right arm - left arm \* Lead II: right arm - left leg \* Lead III: left arm - left leg

Question 52

What are the ECG waves?

Answer 52

\* P - atrial depolarisation \* QRS complex - ventricular depolarisation/arial repolarisation \* T - ventricular repolarisation

Question 53

What are the ECG intervals?

Answer 53

\* PR interval: AV node delay \* ST segment: ventricular systole \* TP interval: diastole