UCL PHOL1001: Topic 7 - Cardiovascular System

The action potentials in the heart are about 100 times longer than those of skeletal muscle. - ANS True The action potential of skeletal muscle is about 2 ms in duration while the action potentials of the heart cells range from about 150 ms in the cells of the SA node to about 300 ms in a Purkinje fiber. The cells of the sinoatrial node have a steady resting potential of -90 mV. - ANS False The membrane potential of the SA node cells is low, about -60 mV, while that of ventricular cells is about -90 mV. The cardiac action potential is conducted through the myocardium entirely via specialized conducting fibres. - ANS False Although the conduction of the cardiac impulse through the atria occurs preferentially via certain fiber bundles, these cells are normal atrial myocytes. The spread of cardiac excitation is delayed by about 0.1 s at the atrioventricular node. - ANS True The conducting tissue of the heart is composed of specialized cardiac myocytes linked by gap junctions. - ANS True In the ventricles, the specialized conducting cells are the bundle cells and the Purkinje fibers, which transmit their action potentials to ventricular myocytes via gap junctions. The P wave of the ECG reflects atrial contraction. - ANS False