THE HEART

Pacemaker Potential

Slow depolarization of the membrane due to sodium inflow through funny channels and reduced potassium outflow.

Depolarization (Action Potential)

Rapid depolarization occurs when calcium channels open and calcium rushes in once threshold (around –40 mV) is reached.

Repolarization

Process where calcium channels close and potassium channels open, allowing potassium to flow out and bringing the membrane potential back down.

Intrinsic Cardiac Conduction System

Network of autorhythmic cells that coordinates depolarization and contraction throughout the heart.

Sinoatrial (SA) Node

The pacemaker located in the right atrium, generating an electrical impulse about 75 times per minute.

Atrioventricular (AV) Node

Delays the impulse for about 0.1 seconds to allow atrial contraction to complete.

Atrioventricular (AV) Bundle (Bundle of His)

The only electrical connection between the atria and ventricles.

Bundle Branches

Right and left branches that carry the impulse through the interventricular septum.

Purkinje Fibers

Fibers that spread through the ventricles and cause coordinated contraction from apex to base.

Sympathetic Nervous System

Increases heart rate and contractility via norepinephrine.

Parasympathetic Nervous System

Decreases heart rate via acetylcholine, primarily through the vagus nerve.

Cardioacceleratory Center

Part of the cardiac centers in the medulla oblongata that activates sympathetic neurons to speed up the heart.

Cardioinhibitory Center

Activates parasympathetic fibers in the vagus nerve to slow down heart rate.

Long Refractory Period

Prevents tetanus in cardiac muscle contraction.

Sarcoplasmic Reticulum

Source of calcium influx during cardiac muscle action potential.