Modern humans and Neanderthals show an average cranial capacity of around 1400–1500 cc. 

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#Unit 7. System Physiology – Animal

Fourth heart sound (S4)

Not audible in normal adults

Heard in ventricular hypertrophy, where ventricular compliance is decreased

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#Unit 7. System Physiology – Animal

Isovolumetric Ventricular Contraction

Initiates contraction of the ventricles

Intraventricular pressure rises sharply as the myocardium presses on the blood in the ventricle

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#Unit 7. System Physiology – Animal

Isovolumetric Ventricular Contraction As soon as ventricular pressure exceeds atrial pressure, the AV valve closes. 

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#Unit 7. System Physiology – Animal

Closure of the AV valves produces the first heart sound (S1).

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#Unit 7. System Physiology – Animal

During isovolumetric Ventricular contraction, the volume of the ventricle does not change because all valves are closed.

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#Unit 7. System Physiology – Animal

Period of isovolumetric ventricular contraction lasts, until the pressures in the left and right ventricles,exceed the pressures in the aorta & pulmonary artery.