1. Heart tissue Endocardium (internal layer) Myocardium (middle – muscle)
Epicardium (external layer)

2. Cardiac muscle Myocardium (heart muscle)
Specialized for coordinated contraction
Involuntary muscle tissue but with striations
Qualities of skeletal and smooth muscle
“Pacemaker” cells fire without neuronal innervation

3. Has a branching or “Y-shaped” structure

4. Intercalated discs Fibrous connections between myocardial cells
Fuse cells to one another for strength during contractions
Also contain “gap junctions”
Gap junctions connect myocardial cytoplasm allowing propagation of action potentials to move continuously from one cell to the next
“electrical synapses”

5. Only about half of your muscle cells will regenerate over your lifetime.
So….
Umm….
Take care of them!

6. Exam on Thursday
Review heart conduction system
Review blood types and Rh factor
Universal donors and recipients
Heart conditions
Blood type worksheet and finish heart conduction system worksheet

7. Cardiac Cycle
Systole – Ventricles contract forcing blood to the lungs and body
Diastole – Ventricles relaxed and filling with blood

8. Intrinsic conduction system

9. Pacemaker cells Conduction sequence
Myocardial cells that generate action potentials
SA node, AV node, Bundle of His
All can generate action potentials but usually superseded by SA impulse signal
Cells “slowly” depolarize from resting potential causing their own action potential
Conduction system is composed of myocardial cells specialized for electrical conduction.
Conduction sequence
SinoAtrial (SA) node
Atrial contraction
Atrioventricular (AV) node (.12s pause)
Bundle of His
Left and right bundle branches
Purkinje fibers
Ventricular contraction