Unit 3: Heart MicroAnatomy & Physiology

Cardiac Muscle

A type of striated muscle found in the heart, responsible for contracting and pumping blood.

Cardiac Monocytes

Contractile cardiac muscle cells, also known as cardiac muscle fibers.

Striated Muscle

Muscle tissue that has a striped appearance, due to the presence of sarcomeres.

Sliding Filament Model

A mechanism explaining how muscle contraction occurs through the sliding of actin and myosin filaments.

Intercalated Discs

Structures that connect adjacent cardiac muscle cells, facilitating coordinated contractions.

Desmosomes

Junctions that physically connect cardiac myocytes, providing mechanical stability.

Gap Junctions

Electrical and chemical connections between cardiac myocytes, allowing ion and signal sharing.

Syncytium

A functional mass of interconnected cardiac muscle cells that behave collectively as one unit.

Autorhythmic Cells

Cells in the heart that can generate action potentials independently of external stimuli.

L-Type Calcium Channels (LTCC)

Channels in T-tubules that allow calcium influx during cardiac muscle action potential.

Calcium-Induced Calcium Release

Mechanism where calcium influx triggers additional calcium release from the sarcoplasmic reticulum.

Calcium ATPase (CIRCA) Pump

A pump that moves calcium back into the sarcoplasmic reticulum after muscle contraction.

Sodium-Calcium Exchanger (NCX)

A transport mechanism that exchanges intracellular sodium for extracellular calcium.

Contractile Cells

Cells that make up about 99% of the myocardium and are responsible for heart contractions.

Pacemaker Cells

Noncontractile cells in the myocardium that generate electrical signals for cardiac contractions.

Sinoatrial (SA) Node

The natural pacemaker of the heart, located in the right atrium.

Funny Current

Depolarization current generated by HCN channels in pacemaker cells.

Internodal Pathways

Pathways that facilitate communication between the SA node and AV node.

Atrioventricular (AV) Node

Pacemaker location that introduces a critical delay between atrial and ventricular contraction.

AV Bundle (Bundle of His)

Structure that conducts impulses from the AV node down the interventricular septum.

Purkinje Fibers

Fiber network that conducts depolarization signals to ventricular contractile cells.

Pacemaker System Fail-safes

Redundant mechanisms in the heart to ensure continued pacing if primary pacemaker fails.

Excitation-Contraction Coupling

The process linking cardiac action potentials to muscle contraction.

Calcium Cycling

The movement of calcium into and out of the cytosol during contraction and relaxation.

Troponin

A protein that binds calcium, allowing actin-myosin interaction for muscle contraction.

Sodium-Potassium Pump (Na+/K+ Pump)

Pump that maintains sodium and potassium gradients essential for cardiac electrical activity.

Preload

The initial stretching of cardiac muscle fibers before contraction.

Afterload

The pressure against which the heart must work to eject blood during contraction.

Heart Rate Regulation

Regulation of the heart rate by the autonomic nervous system.

End Diastolic Volume (EDV)

The volume of blood in the ventricles at the end of diastole, before contraction.

Cardiac Output

The total volume of blood pumped by the heart per minute.

Stroke Volume

The volume of blood ejected during each heartbeat.

Heart Mechanics

Physical processes involving heart chambers, valves, and muscle contractions during the cardiac cycle.