3.2.6 coordination of cardiac cycle

Question 1

bradycardia

Answer 1

slow heart rhythm

Question 2

ectopic heartbeat

Answer 2

extra beat or early beat of ventricles

Question 3

electrocardiogram (ECG)

Answer 3

trace that records electrical activity of heart

Question 4

fibrillation

Answer 4

uncoordinated contraction of atria & ventricles

Question 5

myogenic muscle

Answer 5

muscle that can initiate own contraction

Question 6

Purkyne tissue

Answer 6

consists of specially adapted muscle fibres which conduct wave of excitation from AVN (atrio-ventricular node) down septum to ventricles

Question 7

sino-atrial node (SAN)

Answer 7

heart’s pacemaker - small patch of tissue that sends out waves of electrical excitation at regular intervals to initiate contractions

Question 8

trachycardia

Answer 8

rapid heart rhythm

Question 9

how is cardiac muscle myogenic

Answer 9

can initiate own contraction

Question 10

which muscle contracts at a higher frequency

Answer 10

atrial muscle

Question 11

what initiates & controls the heartbeat

Answer 11

sino-atrial node (SAN)
- at top of right atrium, by vena cava
- generates electrical activity
- initiates waves of excitation at regular intervals

Question 12

role of SAN in contraction of atria

Answer 12

1. wave of excitation spreads over walls of atria
2. travels along membranes of muscle tissue
3. as wave of excitation passes, it causes cardiac muscle cells to contract
   = atrial systole

Question 13

role of atrio-ventricular node (AVN)

Answer 13

• tissue at base of atria unable to conduct wave of excitation = cannot spread directly to ventricle walls
• AVN located at top of interventricular septum
• conducts wave of excitation to ventricles
• wave of excitation delayed in node = time for atria to finish contracting & blood to flow into ventricles

Question 14

role of AVN in contraction of ventricles

Answer 14

1. after short delay, wave of excitation carried from AVN down specialised conducting tissue (Purkyne tissue)
2. tissue runs down interventricular septum
3. at base of septum, wave of excitation spreads over ventricle walls
4. as excitation spreads up from base = muscles contract from base upwards
5. pushes blood up towards major arteries at top of heart

Question 15

describe an ECG trace of a healthy person (look in textbook for diagram pg 197)

Answer 15

• wave P shows excitation of atria
• QRS shows excitation of ventricles
• T shows diastole

Question 16

draw an ECG trace for someone with bradycardia

Answer 16

pg 197

Question 17

draw an ECG trace for someone with tachycardia

Answer 17

pg 197

Question 18

draw an ECG trace for someone with atrial fibrillation (atria beats more frequently than ventricles)

Answer 18

pg 197
- no clear P waves

Question 19

draw an ECG trace for someone with ectopic heartbeat

Answer 19

pg 197

Question 20

normal ECG

Answer 20

sinus rhythm