Cardiovascular Physiology Flashcards
What is a heart contraction?
Electrical impulse that triggers contractile cells
Is a heart contraction intrinsic or extrinsic?
intrinsic (arises from within the heart)
nervous system NOT required
What are the nodes?
clusters of conducting ells that initiate AP in the heart
they have an unstable resting potential (leaky to Na+)
What is the name for the gradual depolarization of nodal cells
prepotential
what happens when threshold is met in the nodal cells?
the voltage gated Ca2+ channels open and a spontaneous AP occurs
List the steps of a conducting cell AP
1) Na+ enters through leak ch. (slow influx)
2) cell develops a prepotential
3) v. gated ca2+ channels open @ threshold
4) rapid influx of ca2+ causes depolarization which causes an AP
5) ca2+ channels close and voltage gated K+ channels open
6) depolarization occurs
How do the AP’s spread beyond the nodal cells to the contractile cells?
gap junctions @ intercalated discs
How are the cells connected?
via desmosomes an anchoring protein which prevents separation
explain and list the electrical pathway that the impulse spreads
1) Sinoatrial (SA) node -In posterior wall of R. Atrium
* goes across internal pathway
2) Atrioventricular (AV) node - floor of R. Atrium
* AP delayed here to allow time for atria to contract
* impuse transmitted to…
3) AV bundle (in the intertribal septum)
4) L + R Bundle branches (in the inter ventricular septum)
5) Purkinje fibers (walls of ventricles)
* Ventricles contract
what is the contraction rate established by the SA node?
100 bpm
so if the SA node wants the heart to beet 100bpm… why doesn’t it?
the parasympathetic system innervates the node - Acetylcholine slows the heart
what happens if the sympathetic system innervates the nodes?
norepinephrine speeds the heart
What would happen if the SA node stopped working
the AV node would fire on its own 40-60bpm
Special aspects of cardiac cell anatomy
- Gap junctions: allow ions to move from cell to cell
- Desmosomes: prevent separation
- Mitochondria: are very fatigue resistant
- Myofibrils: Branch
- NO Terminal cisternae: T tubules release Ca2+ from sarcoplasmic reticulum
Describe the spread of AP to contractile cells
1) Na+ leaks in
2) V. Gated ca2+ ch. open in nodal cells
3) Action potential across nodal cells
4) Cations (+) diffuse into adjacent contractile cells via intercalated discs which house gap junctions
5) this depolarization causes fast v. gated na+ Ch and slow ca2+ channels to open in contractile cells
why are AP slower and more prolonged than in skeletal muscle
-V. gated Na+ channels close quickly
-V. Gated K+ Ch = open
**Repolarization is delayed because voltage gated ca2+ channels in the cell membrane are still open and Ca2+ comes in from the ECF
**This influx also opens ca2+ gated ca2+ channels (like a ligand) in the sarcoplasmic reticulum
**So there is a plateau in membrane potential as ca2+ moves in while K+ moves out
(AP is 30x slower)
Explain the steps of the cardiac muscle cell AP
1) Na+ & ca2+ influx through voltage gated ch.
2) na+ ch. close, k+ ch. open
3) ca2+ influx from ECF & SR and K+ influx -plateau
4) Ca2+ ch. close
5) K+ outflow continues
6) v. Gated K+ ch close (repolarized)
What does it mean that contraction of cardiac muscle cells is coupled to excitation
- Ca2+ enters from SR + ECF
- Ca2+ binds troponin causing tropomyosin to shift
- This allows the cross bridge to form (Myosin binds actin)
- the filaments slide which causes a contraction
- The ca2+ ch are slow to close so the contraction is prolonged
- eventually the ca2+ pumps will put all the Ca2+ back where it came from and outflux of K+ will repolarize the cell
What is meant by a cardiac cycle?
1 complete contraction & relaxation
What is systole
contraction phase (blood pushed out of chamber)
what is diastole
Relaxation phase (chamber fills with blood)
What does an electrocardiogram do?
Records electrical currents (AP’s) during the cardiac cycle
DOES NOT measure muscle contractions: just the electrical events that trigger it
what causes the p wave
atria depolarization then atrial systole occurs in space after
What causes QRS Complex
Ventricles depolarize then after the ventricular systole occurs
(@ same time atria is repolarizing and atrial diastole)
