Download Control of the cardiac cycle

Control of the cardiac cycle
Learning intentions
• Describe how heart action is coordinated with
reference to the sinoatrial node, the
atrioventricular node and the purkyne tissue.
• Interpret and explain electrocardiogram (ECG)
traces with reference to normal and abnormal
heart activity.
What is Your Heart Rate?
• Your pulse is the
number of beats in
15 seconds then
calculate for the
number of beats per
minute
• Complete question 1
on the worksheet.
The need for coordination
• The heart of a mammal contains four main
chambers. The action of these chambers is
coordinated by electrical activity in specialised
tissues that regulate the heart rate.
Coordination of the heart
• The sinoatrial node (SAN) (pacemaker) generates electrical
activity at regular intervals. This causes the atrial cardiac
muscles to contract (atrial systole)
• The atrioventricular node (AVN) delays the electrical activity
to allow blood to flow into the ventricles.
• The Purkyne tissue is a specialised conducting tissue that
spreads the electrical signal to the ventricular muscles causing
them to contract.
T
U
V
The pathway followed by the wave of excitation
Electrocardiograms (ECGs)
• We can monitor the
electrical activity of
the heart using an
electrocardiogram
(ECG).
Electrocardiogran (ECG)
Electrodes are placed on the skin over opposite sides of the heart,
and the electrical potentials generated recorded with time. The
result is an ECG.
P wave = electrical activity during atrial
systole
QRS complex = electrical activity during
ventricular systole
T wave = ventricular repolarisation
(recovery of ventricular walls)
Q-T interval – contraction time
(ventricles contracting)
T-P interval – filling time – ventricles
relaxed and filling with blood
A normal ECG trace compared with others indicating an unhealthy heart
Activity
• Students will answer questions on page 59
• Students will attempt some past paper
questions.