Cardio -2

Vocabulary flashcards covering the cardiac refractory period, prevention of tetany, and left ventricular rotational mechanics.

Refractory period (cardiac muscle)

The interval during which normal cardiac muscle cannot be re-excited by another impulse.

Ventricular refractory period

The normal refractory period of ventricular muscle, lasting approximately $0.25-0.30\,\text{second}$.

Relative refractory period (cardiac muscle)

An additional period lasting about $0.05\,\text{second}$ during which a sufficiently strong stimulus may excite the muscle.

Atrial refractory period

The refractory period of atrial muscle, which is shorter than the ventricular refractory period and lasts about $0.15\,\text{second}$.

Functional importance of cardiac refractory period

Limits immediate re-excitation during contraction and helps coordinate rhythmic pumping.

Mechanism preventing wave summation in cardiac muscle

The prolonged cardiac action potential and refractory period prevent repeated excitation from summing normally during a single contraction.

Consequence of sustained tetanic contraction in cardiac muscle

Interferes with the alternating contraction and relaxation needed for effective pumping.

Clinical significance of the cardiac refractory period

Essential for rhythmic cardiac pumping; unlike skeletal muscle, cardiac muscle cannot normally be driven into sustained tetanic contraction by rapid repetitive stimulation.

Organization of left ventricular muscle fibers

Arranged in complex layers running in different directions to allow a twisting motion during systole.

Subepicardial fibers

Left ventricular muscle fibers that spiral in a leftward direction.

Subendocardial fibers

Left ventricular muscle fibers that spiral in a rightward direction, opposite to the subepicardial fibers.

Apical rotation during systole

Counterclockwise rotation of the left ventricular apex when viewed from apex to base.

Basal rotation during systole

Clockwise rotation occurring at the base of the left ventricle.

Effect of left ventricular twisting motion

Produces a wringing action that helps pump blood downward toward the apex during systole.

End-systolic ventricular recoil

The process where the left ventricle behaves like a loaded spring that recoils or untwists during diastole.

Functional importance of ventricular untwisting

Helps allow blood to enter the pumping chambers rapidly during diastole.