Chapter 20 Physiology (cardiac conduction system)

30 terms by lshows

Create a new folder

Advertisement Upgrade to remove ads

What is the cardiac conduction system?

*Group of specialized, highly exciteable cells that give the heart its rhythmicity

What are the parts of the cardiac conduction system?

*SA Node
*AV Node
*AV Bundle (Bundle of His)
*Purkinje Fibers

What is the function of the cardiac conduction system?

*To spontaneously generate and conduct action potentials

*These action potentials in turn trigger action potentials in cardiac muscle, allowing the heart to contract

What is the resting Vm of the cardiac conduction system?

-60 mV

What is threshold for the cardiac conduction system?

-40 mV

What occurs during the prepotential phase of action potential generation in the cardiac conduction system?

1. The HCN channels open

-HCN channels are permeable to both K⁺ and Na⁺
-More Na⁺ enters than K⁺ leaves, so the net result is depolarization

2. Threshold is reached, HCN channels close, Voltage Gated Ca²⁺ channels open

-This marks the end of the prepotential phase

What occurs during the depolarization phase of action potential generation in the cardiac conduction system?

1. Threshold has been reached (-40 mV)

2. HCN channels close

3. An action potential (called a PACEMAKER POTENTIAL) has been generated

4. Voltage Gated Ca²⁺channels open

-Ca²⁺enters, causing depolarization

What occurs during the repolarization phase of action potential generation in the cardiac conduction system?

1. Voltage Gated Ca²⁺channel closes

2. Voltage Gated K⁺ channel opens

-K⁺leaves the cell, causing repolarization

By what type of conduction are action potentials transmitted in the cardiac conduction system?

*Via continuous conduction

*These action potentials spread both to the rest of the cardiac conduction system and cardiac muscle cells of the atria and ventricles

Where is the SA Node located?

*In the wall of the right atrium, medial to the opening of the superior vena cava

Which part of the cardiac conduction system is also known as the "pacemaker of the heart"

SA Node

How many action potentials does the SA Node generate per minute?

~ 70 to 80 action potentials per minute

Where does the SA Node spread action potentials to?

*To the cardiac muscle of the right and left atria via the internodal pathways

*To the AV Node via the internodal pathways

Where is the AV Node located?

*Near the interventricular septum in the lower portion of the right atrium

From where does the AV Node receive action potentials?

SA Node

To where does the AV Node send action potentials?

AV Bundle (Bundle of His)

How long is the action potential delayed at the AV Node?

~110 msec

Why is the action potential delayed at the AV Node?

*Allows the atria to complete its contraction before the ventricle begins to contract

*Without this delay, the atria and ventricles would contract at the same time. Since the ventricle is bigger and stronger than the atrium, contracting at the same time would cause the blood to be forced backward from the ventricle into the atrium

Where is the AV Bundle (Bundle of His) located?

*In the interventricular septum, near the atria

*Divides into right and left bundle branches (one per ventricle)

From where does the AV Bundle (Bundle of His) receive action potentials?

*From the AV Node

To where does the AV Bundle (Bundle of His) send action potentials?

*To the Purkinje fibers

Where are Purkinje fibers located?

*Branch superiorly into ventricular myocardium

From where do Purkinje fibers receive action potentials?

*From the AV Bundle (Bundle of His)

To where do Purkinje fibers send action potentials?

*To the cardiac muscle of the ventricles

What is an ectopic pacemaker?

Term used to describe some part other than the SA Node generating the heart's rhythm

What effect does an ectopic pacemaker have on heart rate?

*Can cause the heart rate to slow down or speed up, depending on what area of the heart is acting as the pacemaker

What is the most common ectopic pacemaker?

AV Node

How does the AV Node acting as the pacemaker effect heart rate?

*Slows the heart rate to ~ 40 - 60 beats/min

How does the Purkinje fibers acting as the pacemaker effect heart rate?

*Slows the heart rate to ~ 25 - 45 beats/min

Why does the entire heart still receive action potentials with an ectopic pacemaker?

*Since the myocardium is a syncitium, all parts of it will receive action potentials, regardless of where in the syncitium those action potentials are generated

*In the case of an ectopic pacemaker, the action potentials do reach all of the myocardium but not efficiently, which is why heart rate is effected.

Please allow access to your computer’s microphone to use Voice Recording.

Having trouble? Click here for help.

We can’t access your microphone!

Click the icon above to update your browser permissions above and try again

Example:

Reload the page to try again!

Reload

Press Cmd-0 to reset your zoom

Press Ctrl-0 to reset your zoom

It looks like your browser might be zoomed in or out. Your browser needs to be zoomed to a normal size to record audio.

Please upgrade Flash or install Chrome
to use Voice Recording.

For more help, see our troubleshooting page.

Your microphone is muted

For help fixing this issue, see this FAQ.

Star this term

You can study starred terms together

NEW! Voice Recording

Create Set