**EXAM 3 Heart's Conduction System

Hormones Factors that Regulate HR(2)

~Catecholamines (epinephrine and norepinephrine) increase HR & contractility ~Thyroid hormones increase HR & contractility

Ions Factors that Regulate HR(2)

~High K+ or Na+ decreases HR & contractility ~Ca2+ increases HR & contractility

6 Factors that Regulate HR

~Hormones ~Ions ~Age ~Gender ~Fitness ~Body temperature

Body temperature Factors that Regulate HR(2)

~Increased body temp. (fever, exercise) increases SA node firing, thereby increasing HR ~Oppositely, decreased body temp. decreases HR

Atrioventricular (AV) bundle(3)

(Bundle of His) ~located in superior part of interventricular septum ~Carries impulse from atria to ventricles

Sino-atrial (SA) node(3)

(the "pacemaker") ~SETS HEART RATE ~Travels through both atria which contract simultaneously ~Initiates impulses at a rate of about 75 beats per minute

Right and Left bundle branches

extend through the interventricular septum toward apex of heart ~Transmit impulse to their respective ventricle

Purkinje fibers(3)

located in the inner ventricular walls of the heart, just beneath the endocardium ~Conduct action potential from the apex to the remainder of the ventricular myocardium ~Causes synchronized contraction of ventricles

Sino-atrial (SA) node location

located in the right atrial wall just inferior and lateral to the opening of the superior vena cava

Gender Factors that Regulate HR

males < females

Age Factors that Regulate HR

newborn = 120 bpm adult= 70 bpm

Atrioventricular (AV) node(3)

~The impulse is delayed here ~This "traffic jam" allows the atria to empty their blood into ventricles ~Once past AV node signal spreads rapidly throughout heart

Cardiac center(5)

~in the medulla oblongata ~Receives signals from baroreceptors and chemoreceptors in cardiovascular system ~Sends signals via sympathetic and parasympathetic pathways ~Modifies (does not initiate) cardiac activity •Influences rate and force of heart's contractions

5 steps of the conduction system

1) SA Node fires 2) Excitation spreads through atrial myocardium 3) AV Node fires 4) Excitation spreads down AV bundle 5) Purkinje fibers distribute excitation through ventricular myocardium

Parasympathetic innervation(3)

decreases heart rate ~Starts at medulla's cardioinhibitory center ~Relayed via vagus nerves (CN X) •Right vagus innervates SA node •Left vagus innervates AV node

Sympathetic innervation(3)

increases heart rate and force of contraction ~Starts at medulla's cardioacceleratory center ~Relayed via neurons from T1-T5 segments of spinal cord •Extend to SA node, AV node, myocardium, and coronary arteries •Increases coronary vessel dilation

Conduction system(3)

initiates and conducts electrical events to ensure proper timing of contractions ~Specialized cardiac muscle cells that have action potentials but do not contract ~Its activity is influenced by autonomic nervous system

Atrioventricular (AV) node location

right above the tricuspid valve in the interatrial septum

5 components of the conduction system.

~Sinoatrial (SA) node (pacemaker) ~Atrioventricular (AV) node ~Atrioventricular (AV) bundle (bundle of His) ~Right and Left Bundle Branches ~Purkinje fibers