1. The Mammalian Heart
External and Internal Structure
Mass = 300 g
Muscle = Cardiac muscle
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2. Cardiac muscle
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3. A mammalian heart seen from the
front (External)
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4. Coronary arteries
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5. Vertical section through a
mammalian heart (Internal)
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6. Vertical section through a
mammalian heart (Internal)
(mitral)
• septum
• papillary
muscle
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7. Atrio-ventricular valves
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8. Difference in thickness of the
walls of different chambers and
their functions?
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9. Mammalian circulatory system
Closed double
circulation
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10. Cardiac cycle
* Sequence of events which makes up one heart beat
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11. Heart action control
 Myogenic – naturally contracts and relaxes, not
needing to receive impulses from a nerve to make it
contract
 Important components:
i) sinoatrial node (SAN/pacemaker) – sets the rhythm of
contraction for all other cardiac muscle cells
ii) atrio-ventricular node (AVN) – picks up the excitation
wave as it spreads across the atria and passes it on to
Purkyne tissue
iii) Purkyne tissue – conducting fibres that transmits
excitation wave through ventrical walls
 Fibrillation – heart wall flutters rather than contracting
as a whole and then relaxing as a whole (started by
electric shock or by damage to large areas of muscle in
the walls of the heart)
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12. Fibrillation
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13. Heart action control
Purkyne tissue
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14. Electrocardiogram (ECG)
 Electrodes placed over opposite sides of
the heart and the electrical potentials
generated recorded with time
 ECG – graph of voltage against time
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