Cardiac Muscle & Cardiac Conduction System

What cells make up 99% of the cells in the atria and ventricles?

Myocardial contractile cells

What is the function of the myocardial contractile cells?

Conduct impulses

Contractions that pump blood through the body

What cells make up 1% of the autorhythmic cells?

Myocardial conducting cells

What is the function of the myocardial conducting cells?

Initiate/propagate action potential that travels through heart muscle and trigger contractions

What is the name of the heart cells that are striated, short, thick branched cells with one central nucleus with light-staining mass of glycogen?

Cardiomyocytes

How is most repair of cardiac muscle damage done?

Fibrosis - scarring

What joins cardiomyocytes end to end?

Intercalated discs

What are the three features that intercalated discs use to join cardiomyocytes?

Interdigitating folds

Mechanical junctions

Electrical junctions

What is the function of the interdigitating folds?

Increase surface area and interlock cells

What is the function of fascia adheres of the mechanical junctions?

Actin of thin myofilaments is anchored to plasma membrane

What are the protein channesl that allow ions to flow between cells and can stimulate neighbors?

Electrical junctions

What feature allows the entire myocardium of either 2 atria/vetnricles to act like a single, unified cell?

Electrical (gap) junctions

What does cardiac muscle depend almost exclusively in?

Aerobic respiration

What is cardiac muscle rich in?

Myoglobin (oxygen storage) and glycogen

T/F: The cardiac muscle is adaptable to different organic fuels when oxygen supply is limited.

True

Why is cardiac muscle fatigue resistant?

Makes little use of anaerobic frmentation or oxygen debt mechanisms that lead to fatigue in other muscle types

How can the heart have continuous ATP production?

Rich blood supply

High density of mitochondria

What is the order of the cardiac conduction system?

SA node

AV node

AV bundle (bundle of his)

R/L bundle branches

Purkinje fibers

Where isthe SA node located?

Right atrium near base of SVC

What feature intiates heartbeat and determines heart rate?

Pacemaker - SA node

T/F: Only cardiac muscle cells can directly control heart rate.

True

Pacemakers cells can respond to signals from the _______ to increase or decrease heart rate?

Autonomic nervous system

Where is the AV node?

Near right AV valve at lower end of interatrial septum

What structure is the electrical gateway to the ventricles?

AV node

What is the insulator that prevents currents from getting to ventricles by any other route?

Cardiac skeleton

What serves as the point of attachment for the heart valves?

Cardiac skeleton

Where do the right and left bundle branches pass through?

Interventricular septum toward apex

What is another name for the Purkinje fibers?

Subendocardial conducting networks

Where do the Purkinje fibers spread?

Throughout ventricular myocardium

T/F: There is a high density of gap junctions in the cardiomyocytes of the ventricles.

True

What is the effect of sympathetic innervation to the heart?

Increase heart rate AND contraction strength

Where do sympathetic postganglionic fibers pass through?

Cardiac plexus in mediastinum

Where do sympathetic fibers terminate?

SA and AV nodes

Atrial and ventricular myocaredium

What is the impact of parasympathetic innervation?

Slow heart rate

T/F: The cardiac parasympathetic innervation impacts both contractile strength and heart rate.

False - only heart rate!

Where does the sympathetic pathway to the heart begin?

Nuclei of vagus nerve in medulla oblongata

What do fibers to the right vagus nerve lead to?

SA node

What do fibers to the left vagus nerve lead to?

AV node

T/F: There is little or no vagal stimulation of the myocardium.

True