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Heart (Action potential (SAN action potential: less steep phase 0, less…
Heart
Action potential
SAN action potential: less steep phase 0, less polarized and upsloping phase 4
Gap junctions allow for electrical signals to pass cell to cell
Automaticity
Na+ open and in
Voltage gated Ca2+ open: in
+ive: Ca2+ close
K+ volage channels open, efflux repolarises cell
K+ close
No real resting potential
Ca2+
Sympathetic steepens phase 4, parasympthatic flattens it
Cardiac Cycle
Endocardium: endothelial cells
Myocardium: myocytes
Epicardium: mesothelial cells and connective tissue
Pericardium: fibrous sac, encloses heart
Muscle striated like skeletal muscle
Branched
1, Atrial systole
2, Isovolumetric ventricular contraction (all valves close, no voln change)
3, Rapid ventricular ejetion
4, Isovolumetric ventricular relaxation
5, Rapid ventricular filling
6, Atrial contraction
Cardiac conduction
ED:
SAN fires
Atria contract (15% ventricular filling)
AV node delays conduction
Systole
:
Rapid transmission of impulses through ventricles
Co-ordinated ventricular contraction
K+ out
+
Na +
and Ca2+ in
voltage gated sodium channels open
Then close, some K+ efflux
+ive: K+ volt channels open
Ca2+ in, K+ out:
Ca2+ channels close
Pumps restore
ERP
: Effective:end, second stimulus=action potential
ARP
: Absolute: second stimulus, nothing
QT INTERVAL
P: Atria depolarise
Q:
R: Ventricles depolarise
S:
T: Ventricles repolarise
Terms
Repolarisation: change in membrane potential, returns it to a negative value just after depolarisation phase
Pressure
Left
Low: blood left ventricle via mitral,
depolarization wave, left (+right) ventricle contracts
pressure increases > atria .
AV (S1 lub) + SL valves closes
Aortic pressure decreasing
Ventricular pressure >, aortic valve opens
Both pressures rising together-ish
Muscle repolarises, vent relaxes
Aorta and ventricular pressures decrease
Aortic press (resistance)>ventricular press, SL valve closes (S2 dub)
-AV valves open
Recoil in aorta (contraction) (elastic energy)
Aorta pres>ventricular
Aortic valve closes: dub
snapback blood: aortic valve, slight increase pressure
Decrease pressure
Atrium:
Atria contracts (A wave)
Valves close
Atrial blood crashes off valves (slight increase pressure) (C wave)
Atrial filling up with blood, pressure increases
V: very full left atrium
( Ventricle is filling up and relaxing)
SAN,AVN
Electrical discharge, one muscle fibre to next
Myocyte- myofibril- sarcomeres contract
Gap junctions transmit electrical current between myocytes
Desmosomes provide mechanical strength
Automaticity:
Inititate electrical impulse
Excitability:
respond to electrical impulse
Conductivity:
transmit electrical impulse