1. Science Starter
Which ventricle of the heart has thicker walls, left or right?
Why do you think that ventricle’s walls are thicker?
What makes a heart beat?

2. Today’s Agenda Science Starter Beating Heart Heart Conduction System
ECG & Arrhythmia
Exit Quiz

3. https://youtu.be/NEuSCPifKhA

5. Think, Write, Pair, Share
Take a minute and think about why the heart could beat outside the body
Write down your thoughts
Share with your neighbor
A few volunteers will share their neighbors’ thoughts

6. Unit 5: Cardiovascular System 5.3: Heart Contractions

7. A. The Heart: Conduction System
The heart is not just an inert bundle of muscle
It contains control centers (nodes) and conductive pathways that control its contractions
These pathways can function without input from the nervous system

8. Contraction is initiated by the sinoatrial node
B. Heart Contractions
Contraction is initiated by the sinoatrial node
Sequential stimulation occurs at other autorhythmic cells
“Auto-”: self

9. Sinoatrial (SA) node initiates contraction (L & R Atria contract)
C. Heart Contraction Sequence
Sinoatrial (SA) node initiates contraction (L & R Atria contract)
Impulse from SA node reaches atrioventricular (AV) node, a “delay switch”
AV node sends signal down atrioventricular bundle (AV bundle/Bundle of His)

10. Signal from AV bundle splits at bundle branches
C. Heart Contraction Sequence
Signal from AV bundle splits at bundle branches
Signal travels through Purkinje Fibers, which cause ventricles to contract
Chambers contract as one unit because cardiac muscle cells are electrically linked

11. How do we measure this?
With a device called an EKG or ECG (electrocardiogram)
This is the beep-beep thing in medical tv shows

12. D. ECG – electrocardiogram – a recording of the electrical events (changes) during a cardiac cycle
P Wave – depolarization (contraction) of the atria (atrial contraction – systole)
QRS Complex – depolarization of the ventricles (ventricular contraction, systole)
T Wave – Repolarization of the ventricles

13. E. What happens if this goes wrong?
We get an abnormal heartbeat
A.K.A. an arrhythmia
This can be diagnosed by examining specific portions of an ECG trace
A few examples:
guide.aspx

14. Arrhythmia Dance!

15. Cardiac Conduction Practice
Use the link on my website to practice with cardiac conduction
Mrhoutzscience.weebly.com
Match the heart condition with the EKG strip
Make sure you complete the final question

16. Exit Quiz