The Heart

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The Route of an Action Potential

Step 1:

SA node activation

(Time = 0msec )

Step 2:

Spread across atrial surfaces

(Time = 50msec )

Step 3:

100msec delay at AV node. Atrial contraction.

(Time = 150msec )

Step 4:

Spread down IV septum, bundle branches and purkinje fibers.

(Time = 175msec )

Step 5:

Relayed to myocardium. Ventricular contraction.

(Time = 225msec )

Endocardium

Inner Layer

Lines chambers and valves

Continuous with large blood vessels

Thin squamous epithelium

Endocarditits- inflammation of the endocardium, typically involves heart valves

Myocardium

Specialised cardiac muscle.

Myocarditis- inflammation of the myocardium

Pericardium

Pericardial sac surrounds the heart.

Space inbetween the inner and outer pericardial membranes is filled with pericardial fluid which provides lubrication and prevents friction as the heart beats.

Pericarditis- inflammation of the pericardium.Causes surfaces to rub together and gives a distinct scratching noise that can be heard through a stethoscope.

Epicardium

External layer

Transparent outer part of pericardium

Atrioventricular valves:

Prevent the backflow of blood between the heart chambers.

Heart Valves:

They open and close in response to pressure changes.

Valves open to allow blood flow from the atria into the ventricles.

Stenosis:

Narrowing of the heart valves restricting blood flow.

Semilunar Valves:

Prevent the backflow from the aorta and pulmonary artery back into the heart when the heart contracts.

Action Potential

Layers of the Heart Wall

Valves