Cardio 3 Flashcards
sarcomere
structural and functional subunitof cardiac muscle
Functional syncitium
cardiac muscle fibers connect at intercalated disks which contain gap jxns that allow AP to go through all cells
Are the atria electrically isolated from the ventricles?
yes
Dominant pacemaker in the heart
Sinoatrial (SA) node
Are gap junctions fast or slow?
slow
Bachmann’s Bundle
runs from SA node to left atrium
Where do the three internodal tracts start and end?
Starts at the SA (sinoatrial) and ends at AV (atrioventricular)
What are the three pacemakers of the heart?
- SA node
- AV node
- Bundle of His
Consequence of a damaged His bundle?
depolarization from the atrium to the ventricle could not occur
Specialized conduction pathways of the ventricle (4)
- Bundle of His
- Right bundle branch
- Left bundle branch
- Purkinje fibers
Purkinje fibers
continuations of the depolarization of the bundle branches
Category A animals
Purkinje fibers run on the endocardial surface
ex: dogs, cats, humans
Category B animals
Distance from endocardial to epicardial surface is too far, so the Purkinje fibers expand and branch into the myocardium
ex: horses, ruminants, swine, whales
Which node is bigger - SA or AV?
AV
What category animals is an ECG most useful in?
Category A
4 Major Cations
Sodium, calcium, potassium, magnesium
3 Types of Ion Channels
- Voltage Gated
- Ligand Gated
- Stretch Activated
What ion channel is potassium most involved in?
ligand-gated (and there’s a gazillion of them)
What factors affect ionic curreents in myocardial cells?
number of open channels
current through each channel
probability of each channel being open
Which type of cells have the longest action potential duration: nerve, cardiac, or skeletal muscle?
Cardiac
Resting cell membrance potential in myocardial cells
dependent on the sodium-potassium pump (which depends on ATP which depends on oxygen delivery)
negative
Why is the AP of cardiac cells longer?
Calcium moving into the cell
Label where each phase occurs
0 1 2 3 4
Phase 0
Opening of sodium channels
Phase 1
inactivation of sodium channnels and activation of potassium channels
Phase 2
Calcium channels open (balanced by outward flow of potassium)
Phase 3
Repolarization, the closure of calcium and potassium channels
Phase 4
resting membrane potential
Action potential
rapid change in transmembrane potential (depolarization) followed by rturn to resting membrane potential (repolarization)
Match the cation permeability to the graph.
Calcium. Potassium. Sodium.
- Potassium
- Sodium
- Calcium
3 Main Pacemaker Cells IN ORDER
- SA node (fastest)
- AV node
- Bundle of His and Purkinje fibers
Fast response APs in Cardiac Cells
Atrial and ventricular myocytes (contractile cells, lots ofactin and myosin)
Size of SA node in cells?
approximately 150
Why do ventricular myocytes have slightly longer APs than atrial myocytes?
Ventricular cells need to generate more pressure with more contractile work so need more calcium
What phase sets the heart rate?
Phase 4
What type of cells have a significant slope to their phase 4?
Slow APs, like SA and AV nodes
Acetylcholine effect on heart rate
decreases heart rate
(lengthens interval between APs)
Norepinephrine effect on heart rate
increases heart rate
(shortens interval between APs)
Which increases heart rate - sympathetic or parasympathetic response?
Sympathtic (fight or flight)
(this is how your body has control over heart rate)
Effective Refractory Period (ERP)
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
Relative Refractory Period (RRP)
time during which an action potential could occur but depolarization varies (b/n phases 3 and 4)
Why does all myocardial tisse have long relative refractory periods?
Cardiac cells need rest between contractions, to get nutrients delivered and waste products removed (prevents tetany)
Flow of Excitation/APs in the Heart
SA node –> internodal fibers –> AV node atrial excitation –> bundle of His –> bundle branches –> Purkinje fibers –> ventricles ventricular excitation
Explain some differences you see here.
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
