Midterm paper

MODULE 4 LO1 Nodal Cells

Dr. Lisa Brinn [email protected]

1. Coordination of Cardiac Contractions • Contraction cycles

v Systole - contraction v Diastole – relaxation

• Chamber pressure v Rises v Falls

• Help comes from: v AV valves

o Blood flows out of atria ➙ ventricles Ø AV valves are open Ø Atrial pressure ↑ ventricular pressure

v Semilunar valves o Blood flows out of ventricles ➙ arterial trunks

Ø Semilunar valves are open Ø Ventricular pressure ↑ arterial pressure

Proper timing of atrial and ventricular contractions

↓ • Elaborate pacemaking • Conduction systems

Types of Cardiomyocytes A. Nodal (conductive) cells • Pacemakers

B. Contractive cells • All other cardiomyocytes

Nodal (Conductive) Cells • Are autorhythmic

v Definition: o Inherent ability to generate and conduct impulses

o Cardiac muscle tissue contracts on its own ↓

Alter basic rhythm of contraction

Heart Pacemaker Cells • Specialized cells that spontaneously depolarize = action potential ➙ cells contract

v Sinoatrial (SA) node o Spreads into atria (internodal pathways)

v Atrioventricular (AV) node o Spreads down to heart apex

SA node

AV node

Fibrous tissue

➙ Spreads to atria↑

Purkinje fibers (located at the apex)

↑

Bundle of His

Right and left bundle branches

↑

↑

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Action Potential at SA Node

-5mV 🟰

-40mV

-60mV 🟰

🟰

🟰 🟰

3Na+

2K+

↑

↓ ⥥ K+

⥥Na+

+20mV 🟰⥥Ca++ -60mV

⥥ K+

🟰

Sinoatrial and Atrioventricular Nodes Components of Conducting System

SA node Contains pacemaker cells that initiate the electrical impulse that results in a heartbeat

Internodal pathways

Are conducting fibers in the atrial wall that conduct the impulse to the AV node while simultaneously stimulating cardiac muscle cells of both atria

AV node Slows the electrical impulse when it arrives from the internodal pathways

AV bundle Conducts the impulse from the AV node to the bundle branches

Left bundle branch

Extends toward the apex of the heart and then radiates across the inner surface of the left ventricle

Right bundle branch

Extends toward the apex of the heart and then radiates across the inner surface of the right ventricle

Moderator band

Relays the stimulus through the ventricles to the papillary muscles, which tense the chordae tendineae before the ventricles contract

Purkinje fibers

Convey the impulses very rapidly to the contractile cells of the ventricular myocardium

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