Heart Week 1 Flashcards
What is the sarcolemma?
The thin, continuous cell membrane that binds muscle cells.
What is the Z band?
every 2.5 micrometers, the line that delimits the sarcomere.
What is the A band? H band? I band?
A: region of myosin (thick filament)
H: portion of sarcomere that is free of thin filament
I: region without myosin, encompasses the Z line.
What are T tubules?
Deep invaginations of the cell membrane which help to propagate the AP to deep fibrils.
No T tubules equals what?
No contraction, even though the contraction machinery involves Ca++.
What is held in the sarcoplasmic reticulum?
Ca++
What does Ca++ bind to?
Troponin, allowing for cross bridges.
What is SERCA?
Smooth Endo(sarco)plasmic Ca++. These are the pumps that return the Ca++ to the SR.
What is the role of troponin and tropomyosin? How does Ca++ affect these proteins?
Troponin and Tropomyosin block cell contraction. Ca++ inhibits the inhibitor.
What are the steps of the ATP/myosin action stroke?
- ADP and Pi weakly bind to myosin to actin
- loss of Pi leads to strong binding and power stroke
- ADP is released
- ATP binds and dissociates the actin/myosin bond.
- ATP hydrolysis changes the head angle
Do motor units fire synchronously or asynchronously? Why?
Asynchronously so that the summation maintains a constancy.
What is the difference between TnT, TnI and TnC?
All are troponin.
TnT: links troponin to the actin and tropomyosin complex
TnI: inhibits the ATPase activity of the actin/myosin interaction
TnC: where Ca++ binds
What is tropomyosin?
The wire-like structure that winds around actin and prevent myosin from binding to the actin.
What is an example of a catecholamine?
Epinephrine.
What type of G proteins are beta-adrenergic and muscarinic receptors attached to?
beta-adrenergic: Gs for stimulation of cAMP and activating protein kinases
muscarinic: Gi for inhibition of cAMP.
What is the rate of the SA node, AV node, and Purkinje fibers?
SA: 60-100 bpm
AV: 50-60 bpm
Purkinje: 30-40 bpm
How can beta-adrenergic receptors affect pacemaker cells?
They increase the probability that the pacemaker channels are open, leading to a steeper phase 4 slope, and more rapid firing.
How does sympathetic activity affect pacemaker cells?
- increases rate of depolarization
2. makes the threshold potential more negative
What is an escape beat? Escape rhythm?
When the SA node slows it’s beat, another pacemaker can fire, making sure that the heart beat doesn’t become pathologically slow. Many escape beats make up an escape rhythm.
What is an ectopic beat?
When a latent pacemaker begins to beat faster than the SA node. It is a premature beat.
How can a myoctye become a pacemaker cell?
If they become leaky. They may lose ions quickly, never repolarize as much, and fire more rapidly than the SA node, making for ectopic beats.
What is a conduction block? Name two types.
A region of the heart that is electrically unexcitable. It can be uni or bi-directional.
What is the difference between the parietal and visceral layers of the heart?
Bunch a balloon…
Visceral: the surface touching your first (the heart)
Parietal: the outer surface.
What is the endocardium?
Smooth membrane lining the inside of the chambers of the heart.
What is the only ion that has a high intracellular concentration at rest?
K+
How do Na+ channels work?
They have two gates each, and each gate must be open for Na to enter or exit.
What maintains phase 2?
The influx of Ca++
What leads to the repolarization?
K+ leaving the cell.
What is the resting potential of myocytes as compared to pacemaker cells?
myoctytes: -90mV
pacemakers: -60mV
What determines the force of cardiac contraction?
intracellular Ca++ levels.
What is the function and ratio of the Ca/Na exchanger?
Fxn: Pump Ca++ out of cell. Uses ATP. Depends on both concentration and electrical gradients.
Ratio: 3 Na+ in and 1 Ca+ out.
Tell me about the Ryanodine receptor.
Found on the sarcoplasmic reticulum, it facilitates calcium mediated calcium release. Needed for muscular contractions. It requires ATP.
What are the two phases of systole?
- Isovolumetric: both valves are closed, volume stays the same, pressure increases
- Ejection: aortic/pulmonary valves open and blood flows out.
What is diastole?
When the ventricle is relaxed.
What are the three phases of diastole?
- isovolumetric relaxation: just after ejection, both valves are closed, and pressure is releasing
- Filling 1: mitral valve opens bc atrial pressure is greater than ventricular pressure, blood flows in passively
- Filling 2: atrial contraction purges remaining blood with contraction
What makes the “lub” sound?
closing of the AV valves (tricuspid and mitral)
What makes the “dub” sound?
closing of the semilunar valves.
What is the stroke volume? What is normal resting value?
Volume of blood pumped per beat of the heart.
End Diast - End Syst = Stroke Vol
Normal Resting = ~70ml (3 fl. oz or 2 shots of whiskey)
What is ejection fraction? What is the normal resting value?
(stroke volume)/(end diastolic volume) = ejection fraction
NRV = 0.5-0.7 (50-70%)
NRV for ejection fraction increases with fitness and decreases with heart disease.
What is Cardiac Output? What is the NRV?
stroke volume x heart rate = cardia output
NRV = 5 L/min
NRV for cardiac output scales up with size
Where is norepi used?
In the sympathetic system, and only in the synapse between the post-ganglionic cell and the effector organ, everything else uses ACh.
Where are the preganglionic neurons?
In the lateral horn.
