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

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

Has a branching or “Y-shaped” structure

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”

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

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

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

Intrinsic conduction system

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cells that generate action potentials SA node, AV node, Bundle of His All can generate action potentials but usually superseded by SA impulse signal Cells “slowly” depolarize from resting potential causing their own action potential Conduction system is composed of myocardial cells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