Download 1110 Cardiac Cycle

Science Starter
1. Which ventricle of the heart has thicker walls, left
or right?
2. Why do you think that ventricle’s walls are thicker?
3. What makes a heart beat?
Today’s Agenda
• Science Starter
• Beating Heart
• Heart Conduction System
• ECG & Arrhythmia
• Exit Quiz
• https://youtu.be/NEuSCPifKhA
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
Unit 5: Cardiovascular System
5.3: Heart Contractions
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
B. Heart Contractions
 Contraction is initiated by the
sinoatrial node
 Sequential stimulation occurs at
other autorhythmic cells
“Auto-”: self
C. Heart Contraction Sequence
1. Sinoatrial (SA) node initiates contraction (L
& R Atria contract)
2. Impulse from SA node reaches
atrioventricular (AV) node, a “delay switch”
3. AV node sends signal down
atrioventricular bundle (AV bundle/Bundle
of His)
C. Heart Contraction Sequence
4. Signal from AV bundle splits at bundle
branches
5. Signal travels through Purkinje Fibers,
which cause ventricles to contract
• Chambers contract as one unit because
cardiac muscle cells are electrically linked
How do we measure this?
• With a device called an EKG or ECG
(electrocardiogram)
• This is the beep-beep thing in medical tv shows
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
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:
• http://www.practicalclinicalskills.com/ekg-referenceguide.aspx
Arrhythmia Dance!
• http://youtu.be/r9yUIDNmCsw
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
Exit Quiz