Conduction Flashcards
Which circuit does the right side of the heart go to?
Pulmonary
What is the pressure in the pulmonary circuit?
Low
What is the relative resistance in the pulmonary circuit?
Low
Why doesn’t the right side of the heart need to contract as strong as the left side?
Not going as far
What circuit does the left side of the heart go to?
Systemic
What is the pressure in the systemic circuit?
High
What is the relative resistance in the systemic circuit?
High
What controls the heart rate?
Pacemakers
What are the two types of pacemakers?
Neurogenic and myogenic
What is a neurogenic pacemaker? What animals use it?
Heart rate is controlled by the brain and contractions are initiated by neurons. Used by invertebrates
What is a myogenic pacemaker? What animals use it?
Contractions are initiated by cardiac myocytes. Used by vertebrates
What are pacemakers?
Cells that produce spontaneous, rhythmic depolarizations that initiate contractions
How do cardiac myocytes spread a depolarization from one cell to another?
Gap junctions
Which pacemaker cells will determine the heart rate?
The one with the fastest intrinsic rhythm
How do neurogenic pacemakers work?
Pacemaker neurons are contained in cardiac ganglion. A sequential firing of neurons from anterior to posterior initiates a series of contractions. The heart rate is controlled by the brain
What are the 4 nodes in vertebrate hearts? What order do they fire in?
SA node
AV node
Bundle of His
Purkinje fibres
How is the signal spread between nodes in a vertebrate heart?
Gap junctions
Which node initiates the contractions?
SA node
What happens when the SA node fires?
The signal moves from the right atrium to the left atrium and they both contract at the same time. At the same time, the signal follows an internodal pathway at a slight delay to the AV node
Where is the SA node located?
Right atrium
Why is the AV node delay so important?
Allows contraction of the atria for the ventricles to fill completely before the ventricles contract
What happens once the AV node fires?
Signal goes down the left and right branches of the Bundle of His and then the Purkinje fibres spread the signal through the ventricle walls and cause the contraction of the ventricles
What is the entire process of conduction in vertebrate hearts called, including the delay between the SA and AV nodes?
Functional sysncytium
What determines the heart rate in a myogenic heart?
The fastest node, normally the SA node
What would happen to heart rate if the SA node was damaged?
Rate is determined by the AV node instead, which is slower so the heart rate is slower too
What would happen if the AV node was damaged?
Rate will still be driven by the SA node, but there will be a much longer delay between the initial signal and ventricle contraction
What is ectopic focus?
The Purkinje fibres fire much faster than the SA node, so the heart rate is driven by that instead
What is conduction?
Spread of an electrical signal through nerves or muscles via the movement of ions
What is depolarization?
Reversal of charge across the cell membrane caused by rapid ion movement
What is the ion balance in myocytes?
Low calcium, low sodium, and high potassium inside the cells
What are the sodium channels in myocytes called? How are they gated?
Funny channels, voltage gated
How does sodium permeability change in a myocyte throughout an action potential?
Low permeability during repolarization and right after a depolarization. Sodium channels open to cause the depolarization and close at the highest membrane potential
How does potassium permeability change in a myocyte throughout an action potential?
High permeability right after a depolarization and lowers during the plateau phase and increases again during repolarization
How does calcium permeability change in a myocyte throughout an action potential?
Increases during a depolarization and decreases right after
How does acetylcholine affect heart rate?
Decreases depolarization rate and heart rate
What is the receptor of acetylcholine?
Muscarinic receptor
What effect does acetylcholine have on pacemaker cells?
Increases potassium efflux and decreases calcium influx
How does epinephrine and norepinephrine affect heart rate?
Increases depolarization rate and increases heart rate
What effect does epinephrine and norepinephrine have on pacemaker cells?
Opens the voltage gated sodium and calcium channels and allows ion influx into the cell
