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?

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 http://www.healthcentral.com/heart-disease/animation-44725-71.html

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

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

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)

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

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 http://youtu.be/RYZ4daFwMa8

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-reference- guide.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