Unit 5 - for Edexcel A level biology

1. Electrical activity of the heartElectrical activity of the heart

2. Interatrial pathway
Right atrium Left atrium
SA node
Internodal
pathway
AV node
Purkinje
fibers
Right ventricle Left ventricle
Bundle
of His

3. Sinoatrial
(SA) node
Right
atrium
Internodal
pathway
Right
branch
of bundle
of His Right
ventricle Purkinje
fibers
Left
branch
of bundle
of His
Left
atrium
Atrioventricular
(AV) node
Interatrial
pathway

8. Artificial Pacemaker • External Defibrillator

9. Conduction Of Cardiac Excitation Wave:-Conduction Of Cardiac Excitation Wave:-

11. The Sinoatrial node (SA node) is the normal Pace maker
of the heart
(the heart rate is set by SA node=70 beats/minute)
• In cases of damage of the SA node the next slower
pace maker will take the lead i.e. the AV node and the
heart rate will be slower (about 50/minute)
• If the AV node is damaged ,and SA node is
functional ,the atria will contract according to SA
node rate (70/minute) and the ventricles will contract
according to the purkinje rate (30/minute) this
condition occur in complete heart block (complete
atrio-ventricular dissociation) and it is live threatening
condition unless treated by implantation of artificial pace
maker set at normal SA node rate to drive the whole
heart
Ectopic focus:
Sometimes other area than SA node depolarize at faster
rate may arise from hyperexcited purkinje fiber or
any other cardiac tissue and it causes an abnormal

12. Cardiac Muscle can not be tetanized:Cardiac Muscle can not be tetanized:
Tetanus: this is continuous maximal contraction
without relaxation due to stimulation by rapid repetitive
stimuli
• Tetanus can not occur in cardiac muscle but can occur in
skeletal muscle
• Tetanus is fatal if occur in cardiac muscle because the
heart muscle relax to fill with blood before it contracts to
eject this blood

13. Refractory period: Period of time during which excitable
tissues can not be re -excited whatever the strength of the
2nd
stimulus is
The heart has a long refractory period (250 msec)
almost all the period of contraction (300msec) ,unlike
the skeletal muscle which has a shorter refractory period
and a 2nd
stronger stimulus can produce another
contraction
NB) Cause of long refractory period of cardiac muscle in
inactivation of Na+ channels during the long plateau phase
of action potential and remain inactive till the membrane
potential repolarizes back to the resting level

14. ARRYTHMIA : Irregular heart beat
TACHYCARDIA : Heart beat over 100 beats
per minute
BRADYCARDIA : Heart beat less than 60
beats per minute

15. SINOATRIAL NODE FAILURE : P waves
are missing , erratic QRS complex

17. T wave inversion
can be seen when one
suffers from CVD
ST segment lies
below the normal
during angina

19. P wave elevation Pulmonary hypertension ,
blood pressure in the lungs is
much higher than normal

20. Ventricullar fibrillation
Is a condition in which the hearts
electrical activity becomes
disordered
Collapse and sudden death will
follow in minutes unless medical
help is provided