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Cardiac Muscle and the Cardiac Conduction System
Overview
40
Anatomy
Undergraduate 1
02/28/2013

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Cards

Term
What is the average heart rate
Definition
75bpm
Term
What does it mean if our heartbeat is myogenic
Definition
It originates within the heart (in vertebrates)
Term
Why is the heart not dependent on the nervous system for rhythm?
Definition
It has its own pacemaker and electrical system
Term
True or false - both heart muscle and skeletal muscle are striated?
Definition
True
Term
How would you describe the appearance of cardiocytes
Definition
Relatively short, thick, branched cells
Term
Do cardiocytes have a nucleus?
Definition
Yes - centrally placed
Term
Is sarcoplasmic reticulum less developed in skeletal muscle or cardiocytes?
Definition
Cardiocytes - they lack terminal cisternae
Term
What is unusual about the mitochondria of cardiocytes?
Definition
They are especially large
Term
What are intercalated discs?
Definition
Thick connections that join cardiocytes end to end
Term
What are the three distinct features of intercalated discs not found in skeletal muscle
Definition
Interdigitating folds, Mechanical Junctions, Electrical junction
Term
What is meant by the fact that intercalated discs have interdigitating folds, and why is this important?
Definition
Plasma membrane at end of cell folded - folds of adjoining cells interlock and increase surface areas of intercellular contact
Term
Why is it beneficial that intercalated discs have interdigitating folds?
Definition
Increases the surface areas of intercellular contact - folds of adjoining cells interlock
Term
What are the two types of mechanical junctions found on intercalated discs of cardiocytes?
Definition
Broad band, and Desmosomes
Term
What are broad band mechanical junctions?
Definition
Actin of microfilaments anchored to plasma membrane, each cell linked to next via transmembrane proteins
Term
What are desmosomes?
Definition
Weld-like mechanical junctions between cells - prevent cardiocytes from pulling apart when contracted
Term
Why are desmosomes important in cardiocytes?
Definition
Prevent cardiocytes from pulling apart when contracted
Term
Why are electrical junctions between cardiocytes important?
Definition
Allow each cardiocyte to electrically stimulate neighbours
Term
What is the purpose of gap junctions on intercalated discs between cardiocytes?
Definition
Form channels where allow ions to flow from cytoplasm on one cardiocyte directly into next
Term
True or false - The entire myocardium of two atria acts as single cell, but does not in ventricles
Definition
False - the entire myocardium of the two atria acts as a single cell, and is the same for the ventricles
Term
Nearly all of the repair of damaged cardiac muscle is through this process
Definition
Fibrosis (scarring)
Term
Cardiac muscle relies almost exclusively on which type of respiration?
Definition
Aerobic
Term
Cardiac muscle is rich in what two molecules that allow it rely almost exclusively in aerobic respiration?
Definition
Myoglobin and glycogen
Term
What percentage of fuel for cardiac muscle comes from fatty acids (when at rest)?
Definition
60%
Term
What percentage of fuel for cardiac muscle comes from glucose (when at rest)?
Definition
35%
Term
What percentage of fuel for cardiac muscle comes from other fuels such as ketones, lactic acid, and amino acids (when at rest)?
Definition
5%
Term
Why is cardiac muscle not prone to fatigue?
Definition
It makes little use of anaerobic respiration or the oxygen debt mechanism
Term
What are the 5 phases of the conduction system of the heart (in order)
Definition
1 - Sinoatrial (SA) node generates signals
2 - Signals from SA node spread throughout atria
3 - Atrioventricular (AV) node acts as electrical gateway to ventricles
4 - Signals leave AV node through AV Bundle (Bundle of His), separates into right and left bundle branches
5 - Purkinje fibres send signals to cardiocytes
Term
What is the sinoatrial (SA) node?
Definition
A pacemaker that initiates heartbeat and determines heart rate
Term
Where is the SA node located
Definition
It is a patch of modified cardiocytes in the left atrium, just under epicardium near the superior vena cava
Term
Where is the atrioventricular (AV) node located?
Definition
Near right AV valve at lower end of interatrial septum
Term
What is the role of the AV node?
Definition
Acts as an electrical gateway to the ventricles
Term
What acts as insulator, preventing currents getting to ventricles by any other route other than through the AV node?
Definition
Fibrous skeleton
Term
What is the Atrioventricular (AV) Bundle (bundle of His)
Definition
The pathway by which signals leave the AV node
Term
What does the AV bundle fork into?
Definition
The right and left bundle branches
Term
Where do the right and left bundle branches go?
Definition
Enter interventricular septum and descend towards the apex of the heart
Term
What are perkinje fibres?
Definition
Nervelike processes that distribute electrical excitation to cardiocytes in the ventricles, from the AV bundle branches
Term
Do perkinje fibres form an more elaborate network in the left or right ventricle?
Definition
Left
Term
Once the Purkinje fibres have delivered the electrical signal to their limits, how do the cardiocytes perpetuate it?
Definition
By passing ion flows from cell to cell through their gap junctions
Term
What type of nerves does the heart receive?
Definition
Both sympathetic and parasympathetic
Term
What is the role of the nerve supply to the heart
Definition
Modify heart rate and contractile strength
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