Conduction

Question 1

Which circuit does the right side of the heart go to?

Answer 1

Pulmonary

Question 2

What is the pressure in the pulmonary circuit?

Answer 2

Low

Question 3

What is the relative resistance in the pulmonary circuit?

Answer 3

Low

Question 4

Why doesn’t the right side of the heart need to contract as strong as the left side?

Answer 4

Not going as far

Question 5

What circuit does the left side of the heart go to?

Answer 5

Systemic

Question 6

What is the pressure in the systemic circuit?

Answer 6

High

Question 7

What is the relative resistance in the systemic circuit?

Answer 7

High

Question 8

What controls the heart rate?

Answer 8

Pacemakers

Question 9

What are the two types of pacemakers?

Answer 9

Neurogenic and myogenic

Question 10

What is a neurogenic pacemaker? What animals use it?

Answer 10

Heart rate is controlled by the brain and contractions are initiated by neurons. Used by invertebrates

Question 11

What is a myogenic pacemaker? What animals use it?

Answer 11

Contractions are initiated by cardiac myocytes. Used by vertebrates

Question 12

What are pacemakers?

Answer 12

Cells that produce spontaneous, rhythmic depolarizations that initiate contractions

Question 13

How do cardiac myocytes spread a depolarization from one cell to another?

Answer 13

Gap junctions

Question 14

Which pacemaker cells will determine the heart rate?

Answer 14

The one with the fastest intrinsic rhythm

Question 15

How do neurogenic pacemakers work?

Answer 15

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

Question 16

What are the 4 nodes in vertebrate hearts? What order do they fire in?

Answer 16

SA node
AV node
Bundle of His
Purkinje fibres

Question 17

How is the signal spread between nodes in a vertebrate heart?

Answer 17

Gap junctions

Question 18

Which node initiates the contractions?

Answer 18

SA node

Question 19

What happens when the SA node fires?

Answer 19

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

Question 20

Where is the SA node located?

Answer 20

Right atrium

Question 21

Why is the AV node delay so important?

Answer 21

Allows contraction of the atria for the ventricles to fill completely before the ventricles contract

Question 22

What happens once the AV node fires?

Answer 22

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

Question 23

What is the entire process of conduction in vertebrate hearts called, including the delay between the SA and AV nodes?

Answer 23

Functional sysncytium

Question 24

What determines the heart rate in a myogenic heart?

Answer 24

The fastest node, normally the SA node

Question 25

What would happen to heart rate if the SA node was damaged?

Answer 25

Rate is determined by the AV node instead, which is slower so the heart rate is slower too

Question 26

What would happen if the AV node was damaged?

Answer 26

Rate will still be driven by the SA node, but there will be a much longer delay between the initial signal and ventricle contraction

Question 27

What is ectopic focus?

Answer 27

The Purkinje fibres fire much faster than the SA node, so the heart rate is driven by that instead

Question 28

What is conduction?

Answer 28

Spread of an electrical signal through nerves or muscles via the movement of ions

Question 29

What is depolarization?

Answer 29

Reversal of charge across the cell membrane caused by rapid ion movement

Question 30

What is the ion balance in myocytes?

Answer 30

Low calcium, low sodium, and high potassium inside the cells

Question 31

What are the sodium channels in myocytes called? How are they gated?

Answer 31

Funny channels, voltage gated

Question 32

How does sodium permeability change in a myocyte throughout an action potential?

Answer 32

Low permeability during repolarization and right after a depolarization. Sodium channels open to cause the depolarization and close at the highest membrane potential

Question 33

How does potassium permeability change in a myocyte throughout an action potential?

Answer 33

High permeability right after a depolarization and lowers during the plateau phase and increases again during repolarization

Question 34

How does calcium permeability change in a myocyte throughout an action potential?

Answer 34

Increases during a depolarization and decreases right after

Question 35

How does acetylcholine affect heart rate?

Answer 35

Decreases depolarization rate and heart rate

Question 36

What is the receptor of acetylcholine?

Answer 36

Muscarinic receptor

Question 37

What effect does acetylcholine have on pacemaker cells?

Answer 37

Increases potassium efflux and decreases calcium influx

Question 38

How does epinephrine and norepinephrine affect heart rate?

Answer 38

Increases depolarization rate and increases heart rate

Question 39

What effect does epinephrine and norepinephrine have on pacemaker cells?

Answer 39

Opens the voltage gated sodium and calcium channels and allows ion influx into the cell