Cardio 3

Question 1

sarcomere

Answer 1

structural and functional subunitof cardiac muscle

Question 2

Functional syncitium

Answer 2

cardiac muscle fibers connect at intercalated disks which contain gap jxns that allow AP to go through all cells

Question 3

Are the atria electrically isolated from the ventricles?

Answer 3

yes

Question 4

Dominant pacemaker in the heart

Answer 4

Sinoatrial (SA) node

Question 5

Are gap junctions fast or slow?

Answer 5

slow

Question 6

Bachmann’s Bundle

Answer 6

runs from SA node to left atrium

Question 7

Where do the three internodal tracts start and end?

Answer 7

Starts at the SA (sinoatrial) and ends at AV (atrioventricular)

Question 8

What are the three pacemakers of the heart?

Answer 8

1. SA node
2. AV node
3. Bundle of His

Question 9

Consequence of a damaged His bundle?

Answer 9

depolarization from the atrium to the ventricle could not occur

Question 10

Specialized conduction pathways of the ventricle (4)

Answer 10

1. Bundle of His
2. Right bundle branch
3. Left bundle branch
4. Purkinje fibers

Question 11

Purkinje fibers

Answer 11

continuations of the depolarization of the bundle branches

Question 12

Category A animals

Answer 12

Purkinje fibers run on the endocardial surface
ex: dogs, cats, humans

Question 13

Category B animals

Answer 13

Distance from endocardial to epicardial surface is too far, so the Purkinje fibers expand and branch into the myocardium
ex: horses, ruminants, swine, whales

Question 14

Which node is bigger - SA or AV?

Answer 14

AV

Question 15

What category animals is an ECG most useful in?

Answer 15

Category A

Question 16

4 Major Cations

Answer 16

Sodium, calcium, potassium, magnesium

Question 17

3 Types of Ion Channels

Answer 17

1. Voltage Gated
2. Ligand Gated
3. Stretch Activated

Question 18

What ion channel is potassium most involved in?

Answer 18

ligand-gated (and there’s a gazillion of them)

Question 19

What factors affect ionic curreents in myocardial cells?

Answer 19

number of open channels
current through each channel
probability of each channel being open

Question 20

Which type of cells have the longest action potential duration: nerve, cardiac, or skeletal muscle?

Answer 20

Cardiac

Question 21

Resting cell membrance potential in myocardial cells

Answer 21

dependent on the sodium-potassium pump (which depends on ATP which depends on oxygen delivery)

negative

Question 22

Why is the AP of cardiac cells longer?

Answer 22

Calcium moving into the cell

Question 23

Label where each phase occurs
0 1 2 3 4

Answer 23

Question 24

Phase 0

Answer 24

Opening of sodium channels

Question 25

Phase 1

Answer 25

inactivation of sodium channnels and activation of potassium channels

Question 26

Phase 2

Answer 26

Calcium channels open (balanced by outward flow of potassium)

Question 27

Phase 3

Answer 27

Repolarization, the closure of calcium and potassium channels

Question 28

Phase 4

Answer 28

resting membrane potential

Question 29

Action potential

Answer 29

rapid change in transmembrane potential (depolarization) followed by rturn to resting membrane potential (repolarization)

Question 30

Match the cation permeability to the graph. Calcium. Potassium. Sodium.

Answer 30

1. Potassium 2. Sodium 3. Calcium

Question 31

3 Main Pacemaker Cells IN ORDER

Answer 31

1. SA node (fastest) 2. AV node 3. Bundle of His and Purkinje fibers

Question 32

Fast response APs in Cardiac Cells

Answer 32

Atrial and ventricular myocytes (contractile cells, lots ofactin and myosin)

Question 33

Size of SA node in cells?

Answer 33

approximately 150

Question 34

Why do ventricular myocytes have slightly longer APs than atrial myocytes?

Answer 34

Ventricular cells need to generate more pressure with more contractile work so need more calcium

Question 35

What phase sets the heart rate?

Answer 35

Phase 4

Question 36

What type of cells have a significant slope to their phase 4?

Answer 36

Slow APs, like SA and AV nodes

Question 37

Acetylcholine effect on heart rate

Answer 37

decreases heart rate (lengthens interval between APs)

Question 38

Norepinephrine effect on heart rate

Answer 38

increases heart rate (shortens interval between APs)

Question 39

Which increases heart rate - sympathetic or parasympathetic response?

Answer 39

Sympathtic (fight or flight) (this is how your body has control over heart rate)

Question 40

Effective Refractory Period (ERP)

Answer 40

Start of action potential until the myocyte can conduct another action potential (b/n phases 0 and up to 3), but would need a much larger voltage

Question 41

Relative Refractory Period (RRP)

Answer 41

time during which an action potential could occur but depolarization varies (b/n phases 3 and 4)

Question 42

Why does all myocardial tisse have long relative refractory periods?

Answer 42

Cardiac cells need rest between contractions, to get nutrients delivered and waste products removed (prevents tetany)

Question 43

Flow of Excitation/APs in the Heart

Answer 43

SA node --> internodal fibers --> AV node *atrial excitation* --> bundle of His --> bundle branches --> Purkinje fibers --> ventricles *ventricular excitation*

Question 44

Explain some differences you see here.

Answer 44

SA node has the steepest slope to Phase 4 since it is the fastest of the pacemaker cells Atrial cells have shorter peaks because they're not contractile myocytes that need lots of calcium Look at the time it takes for the whole heart to be depolarized