The Heart and ECGs

Biology Unit 5

The Heart and ECGs

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Biology Unit 5
Revision Notes
Topic 7: Run for your life
12. Understand that cardiac muscle is myogenic and
describe the normal electrical activity of the heart,
including the roles of the sinoatrial node (SAN), the
atrioventricular node (AVN) and the bundle of His,
and how the use the electrocardiograms (ECGs) can
aid the diagnosis of cardiovascular disease (CVD) and
other heart conditions.
The heart is myogenic ­ the impulse to contract originates within the heart itself from the
The heart has intrinsic rhythmicity
The heart has its own natural "pacemaker" - the SAN which is located in the right atrium
The basic rhythm causes the heart to beat at about 70 bpm.
Regulation of the heartbeat
1. The SAN sets up a wave of electrical excitation (depolarisation) which causes the atria to
contract (atrial systole)
2. Excitation spreads to the AVN
3. The AVN is excited and after a short rest (to allow the ventricles to fill) the wave of
depolarisation passes into the bundle of His
4. The bundle of His carries the excitation from the AVN down the Purkyne tissue
5. This penetrates through the septum of the heart, spreading between and around the
ventricles, and depolarisation causes contraction of the ventricles (ventricular systole)
6. Blood leaves the heart and travels around the body and the lungs.
Text Book: p. 152 - 153

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Biology Unit 5
Revision Notes
Electrocardiograms (ECGs)
An ECG is used to investigate the rhythms of the heart by producing a record of the electrical activity
of the heart. The depolarisation in the heart causes tiny electrical changes on the surface of your skin.
An ECG measures these changes at the surface of your skin.
12 electrodes are attached to the body.…read more


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