Electrical Activity of the Heart

Question 1

<p>What is the calcium store in muscle?</p>

Answer 1

<p>Sarcoplasmic reticulum</p>

Question 2

<p>What forms the electrical connection in the heart?</p>

Answer 2

<p>Gap junctions</p>

Question 3

<p>What are the intercalating disks formed by?</p>

Answer 3

<p>Desmosome followed by gap junction. Desmosome ensures that cells contract at the same time.</p>

Question 4

<p>Why does cardia muscle have a long action potential?</p>

Answer 4

<p>Long refractory period ensures there is no tetanic contraction.Means Ca2+ entry from outside the cell can regulate contraction.</p>

Question 5

<p>How does Ca2+ entry from outside the cell regulate contraction?</p>

Answer 5

<p>impaired thermogenesis and energy expenditure.</p>

Question 6

<p>What are the cells called with an unstable resting membrane potential?</p>

Answer 6

<p>Pacemakers</p>

Question 7

<p>What causes the wave of electrical activity in the non-pacemaker action potential?</p>

<p>Resting membrane potential?</p>

<p>Initial depolarisation?</p>

<p>Plateau?</p>

<p>Repolarisation?</p>

Answer 7

<p>Resting membrane potential - High resting permeability for potassium</p>

<p>Initial depolarisation - Increase in permeability for sodium</p>

<p>Plateau - Increase in permeability for calcium (L - type channels) and decrease in permeability for potassium.</p>

<p>Repolarisation - Decrease in permeability for calcium and increase in permeability for potassium</p>

Question 8

<p>What causes the wave of electrical activity in the pacemaker action potential?</p>

<p></p>

<p>Action potential?</p>

<p>Pacemaker potential (or pre-potential)?</p>

Answer 8

<p>Action potential - increase in permeability for calcium (L-type receptors)</p>

<p>Pacemaker potential (pacemaker potential):</p>

<p>- Gradual decrease in permeability for potassium</p>

<p>- Early increase for permeability for sodium (Pf channels)</p>

<p>- Late increase in calcium in (T-type channels)</p>

<p></p>

Question 9

<p>When do sodium pF channels open?</p>

Answer 9

<p>During repolarisation of the previous action potential</p>

Question 10

<p>How can drugs affect electrical activity of the heart?</p>

Answer 10

<p>–Ca2+-channel blockers – decrease force of contraction – target L type calcium channels – fewer cross bridges formed – smaller strength of contraction</p>

<p>–Cardiac glycocides – increase force of contraction – More calcium comes in - More cross bridges formed– stronger strength of contraction</p>

Question 11

<p>How does temperatureaffect the electrical activity of the heart?</p>

Answer 11

<p>–increases ~10 beats/min/ºC</p>

Question 12

<p>How does hyperkalemia affect the electrical activity of the heart?</p>

Answer 12

<p>Fibrillation and heart block -reduces concentration gradient for potassium – cell starts to depolarise, spontaneous firing of action potentials</p>

Question 13

<p>What is the affect of hypokalaemia on electrical activity of the heart?</p>

Answer 13

<p>fibrillation & heart block (anomalous) – cells start to hyperpolarise – loads of channels open and the cell depolarises.</p>

Question 14

<p>What is the affect of hypercalcemia on electrical activity of the heart?</p>

Answer 14

<p>–Increased HR & force of contraction – more calcium comes in when the channels open – increase force of contraction.</p>

Question 15

<p>What is the effect of hypocalcaemia on electrical activity of the heart?</p>

Answer 15

<p>–Decreased HR & force of contraction</p>

Question 16

<p>What is the function of the sinoatrial node?</p>

Answer 16

<p>Pacemaker - 0.5 metres per second</p>

Question 17

<p>Describe the annulus fibrosis</p>

Answer 17

<p>Non- conduciting insulator between the atria and the ventricles. Action potentialcan only pass through the atroventricular node.</p>

Question 18

Describe the stages shown

Answer 18

Question 19

<p>What is the arterioventricular node?</p>

Answer 19

<p>A delay box - 0.05 m/s</p>

Question 20

<p>What is the function of the bundle of his?</p>

Answer 20

<p>Bundle of his ensures all the ventricle contracts at the same time</p>

Question 21

<p>What is the name given to the fibres responsible for innervating the ventricular cardiac muscle?</p>

Answer 21

<p>•Purkinje fibres</p>

<p>–rapid conduction system</p>

<p>–~ 5 m/sec</p>

Question 22

<p>What is the extracellular effect of an action potential in a single myocyte?</p>

Answer 22

<p>eEokes a very small extracellular electrical potential</p>

Question 23

<p>How are large extra-cellular electrical waves created?</p>

Answer 23

<p>•Lots of small extracellular electrical potentials evoked by many cells depolarising and repolarising at the same time can summate to create large extracellular electrical waves</p>

Question 24

<p>What does each wave correspond to?</p>

Answer 24

<p>P wave corresponds to atrial depolarisation</p>

<p>QRS complex corresponds to ventricular depolarisation</p>

<p>T wave corresponds to ventricular repolarisation</p>

Question 25

<p>What are blocks the result of?</p>

Answer 25

<p>Issues in conduction</p>

Question 26

<p>What are flutters and fibrilations due to?</p>

Answer 26

<p>Errors in rhythm</p>

Question 27

<p>What is characteristic of atrial fibrillation on an ECG?</p>

Answer 27

<p>No distinguishable P wave</p>

Question 28

<p>How does a defibrillator work?</p>

Answer 28

<p>Defibrillator puts all the cells into their refractory state – they are now ready to receive the next action potential</p>