Lecture 7-8 Slides (1spp) - Cardiac Muscle and the Cardiac Cycle

Overview of Heart Anatomy and Cardiac Cycle

• Anatomy of the Heart

  • Includes heart valves

  • Responsible for mechanical events during the cardiac cycle

Mechanical Events of the Cardiac Cycle

• Phases of Cardiac Activity

  • Contraction (Systole)

    • Decrease in volume (↓V), increase in pressure (↑P)

  • Relaxation (Diastole)

    • Increase in volume (↑V), decrease in pressure (↓P)

• Blood flows from high pressure to low pressure areas.

Cardiac Muscle Action Potentials

• Characteristics of Cardiac Muscle Cells

  • Different action potentials compared to skeletal muscle

  • Exhibit plateau phases due to ion movements, primarily calcium (Ca2+).

Autorhythmic Cells and Conducting System of the Heart

• Components

  • SA Node: Primary pacemaker (70 bpm)

  • AV Node: Secondary pacemaker (50 bpm)

  • Purkinje Fibers: Tertiary pacemaker (30 bpm)

• Autorhythmic cells generate spontaneous action potentials.

Electrocardiograms (ECG)

• Components of ECG

  • P wave: Atrial depolarization

  • QRS complex: Ventricular depolarization

  • T wave: Ventricular repolarization

• Important for assessing heart rate, rhythm, and potential conduction issues.

Cardiac Cycle Events

• List of Primary Events

  • Late Diastole: Chambers are relaxed, ventricles fill passively.

  • Atrial Systole: Atria contract, sending additional blood into ventricles.

  • Ventricular Systole: Ventricles contract, ejecting blood.

  • Isovolumetric Contraction: AV valves close, pressure builds without volume change.

  • Isovolumetric Relaxation: Ventricles relax, pressure drops, semilunar valves close.

Important Heart Sounds**

• S1: Closing of AV valves during ventricular contraction.

• S2: Closing of semilunar valves during ventricular relaxation.

Stroke Volume**

• Measured as EDV (End Diastolic Volume) - ESV (End Systolic Volume).

Intercalated Disks in Cardiac Muscle**

• Function as connectors between cardiac muscle cells.

• Contain desmosomes for mechanical support and gap junctions for electrical signaling.