Origin and spread of cardiac excitation Flashcards
Where is the SA node located?
Junction of SVC with the RA.
Where is the AV node located?
Right posterior portion of the interatrial septum.
What do the atrial fibres contain?
Purkinje-type fibres.
What do the atrial fibres do?
Connect the SA node to the AV node.
What are the three bundles of atrial fibres?
- Anterior internodal tract of bachman.
- Middle internodal tract of Wenckebach.
- Posterior internodal tract of Thorel.
What is the AV node continuous with?
Bundle of His.
Describe the bundle of His?
Has two branches:
1. Left bundle branch at top of the interventricular septum.
2. Right bundle branch.
What does the left bundle branch of His divide into?
- Anterior fascicle.
- Posterior fascicle.
Where do the branches and fascicles run?
Subendocardially down either side of the septum and come into contact with the Purkinje system.
What is the conduction system composed of?
- Modified cardiac muscles - fewer striations and indistinct boundaries.
Describe P cells?
Small round cells with few organelles that connected with each other by gap junctions.
What separates the atrial muscle to the ventricular muscle?
Fibrous tissue ring.
Where does the SA node develop from?
Structures on the right side of the embryo.
Where does the AV node develop from?
Structures on the left side of the embryo.
What innervates the SA node?
Right vagus nerve.
What innervates the AV node?
Left vagus nerve.
Where does each sympathetic fibre come from?
Stellate ganglion.
What are vagal fibres?
Endocardial.
What are noradrenergic fibres?
Epicardial.
How does acetylcholine act on the heart?
Presynaptically to reduce norepinephrine release from the sympathetic nerves.
How does neuropeptide Y act on the heart?
Released from noradrenergic endings and may inhibit the release of AcH.
What is the resting membrane potential of myocardial fibres?
-90mV.