Electrical activity of the heart & the cardiac cycle Flashcards
Conduction system of the heart
- cardiac muscles have
- contracile activity
- Auto rhythmicity comes from
- no CNS commands
- myogenic
- Autorhythmic cells
myogenic effect
functioning in ordered rhythmic fashion because of the inherent properties of cardiac muscle rather than specific neural stimuli
pacemaker cells :
- consist of
- Initiate AP’s by
- function of pm
- SA nodes AP/min
- AV nodes Aps/min
- SA and AV
- departing membrane potentials
- coordinate and provide rhythm
- 70-80
- 40-60
Conduction fibres
- AP/min for bundle of his
- Purkinje fibres
- function
- 20-40
- 20-40
- Transmit AP’s (from pacemaker cells to myocardium , 4m/s)
Spread of excitation through heart muscle:
The excitation signal travels to:
- artiums, telling them to contract
- AV node delay signals until artia are empty of blood
- bundle of his carries signals to purkinje fibers
- Purkinje fibers carry signal to ventricles causing them to contract
Interatrial pathway
SA node initiates AP
Right atrium > left atrium (simultaneous contraction)
INTERNODAL PATHWAY:
sends transmission of signals from SA node to AV node
slow delay of 0.1 second therefore atria contract before ventricles
Ventricular excitation
- fast conduction
- down bundle of his
- up pukinje fibres, contract ventricles , contracile cells
Electrocardiogram (ECG)
what does it do
how
record electrical activity of heart
body fluid become conductors ,currents in the body go to the surface
Electrocardiogram (ECG)
arrhythmias
tachycardia = HR increased bradycardia= ↓
Cardiac Cycle
one cycle lasts..
about 0.8 secs
systole 0.3 (35%)
Diastole 0.5(55%)
the four phases of cardiac cycle
- ventricular filling
- Isovolumetric ventricular contraction
- ventricular ejection
- Isovolumetric ventricular relaxation
ventricular filling
-venous return and atrial contraction
AV valves open leading to passive phase
aortic valves close
then increase of volume
results to arterial contraction
Isovolumetric ventricular contraction
- increased pressure as ventricles contract
- AV valves closes
- isovol- no blood entering or leaving
- aortic valve closed
Ventricular ejection
- ventricle contract
- semilunar valves open
- vent pressure keeps ↑ > peak and decline
- aortic p. ↑ > peak and decline
- blood vol. ↓> ejection
