19.3: Cardiac Muscle and the Cardiac Conduction System

Cardiomyocytes

• muscle cells of the heart

• short, thick, branched cells

• branches form a network throughout each pair of heart chambers

What are the main differences between cardiomyocytes and skeletal muscle?

• sarcoplasmic reticulum is less developed in cardiomyocytes

• T tubules are much larger than in skeletal muscle

• skeletal muscle does not have intercalated discs

Skeletal Muscle

• striated

• under voluntary control

• found in muscles used for movement

Smooth Muscle

• smooth appearance

• involuntary control

• found in the internal organs

Cardiac Muscle

• striated

• involuntary movement

• found only in heart

Adheren Junctions

• bands of proteins that connect actin filaments of neighboring cells

Desmosomes

• interlocking proteins that snap neighboring cells together

Gap Junctions

• form pores to allow substances to pass through

How do cardiomyocytes generate the ATP necessary for repeated contractions?

• they utilize aerobic respiration

Sinoatrial Node (SA)

• pacemaker of heart

• patch of autonomic cells in right atrium that initiates each heart beat

Atrioventricular Node (AV)

• group of autorhythmic cells in the interatrial septum of the heart

• relays excitation from the atria to the ventricles

Atrioventricular Bundle

• pathway where signals leave AV node

• forks into right and left branches which enter interventricular septum and go towards apex

Subendocardial branches (purkinje fibers)

• distribute electrical excitation to the cardiomyocytes of the ventricles

Steps in Cardiac Conduction System

1. SA node fires

2. Excitation spreads through atrial myocardium

3. AV node fires

4. excitation spreads down AV bundle

5. subendocardial conducting network distributes excitation through ventricular myocardium