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 ThursdayReview heart conduction systemReview blood types and Rh factorUniversal donors and recipientsHeart conditionsBlood type worksheet and finish heart conduction system worksheet

Systole – Ventricles contract forcing blood to the lungs and body

Diastole – Ventricles relaxed and filling with blood

Cardiac Cycle

Intrinsic conduction system

Pacemaker cells• 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• SA node, AV node, Bundle of His• All can generate action potentials but usually superseded by SA impulse signal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 sequenceSinoAtrial (SA) node

Atrial contractionAtrioventricular (AV) node (.12s pause)Bundle of HisLeft and right bundle branchesPurkinje fibers

Ventricular contraction