Cardiac Contractility and Events of the Cardiac Cycle Flashcards
Describe the contraction of cardiac muscle
Action potential causes L-type channels to open, allowing for influx of calcium from the muchopolysaccharides that sequester calcium in the T-tubule. This calcium binds to ryanodine receptors in SR causing them to open and releasing calcium from the SR
Describe how troponin in Cardiac muscle differes to Skeltal muscle.
Skeletal muscle - troponin is an all or nothing response. In cardiac muscle the amount of calcium that binds to troponin leads to different levels of activity. Therefore the level of contraction depends on how much calcium binds to troponin as you cannot recruit more muscle fibres.
What is an ionotrope
agent that alters the force or energy of muscular contractions
Describe the sympathetic innervation
Acts on entire heart, acts on noradrenaline beta 1 receptors. This causes an increase in cAMP, enhances the calcium influx and promotes storage and release of calcium from SR. While this increases contractility and speed of contraction is also speeds up calcium repackaging.
Drescribe the parasympathetic innervation
Acts on SA note to innervate the atria, the main effect is to decrease heart rate and has an indirect negative ionotropic effect - tends to be pathological.
Describe how summations of cardiac muscle is avoided
There are many refractory periods:
- Absoloute refractory period,
- Relative refractory period,
- Period of supranormal excitability (period where there is a low risk of stimulating another depolarisation). The absolute refractory period lasts as long as the muscle is contracted for so when it is over
Describe how the atrioventricular valves open and what occurs once they have
AV valves open when there is higher pressure in the atrium than in the ventricle, ventricle has to relax. 80% of the ventricular filling then occurs passively as the blood flows from an area of high pressure to low pressure. Atrial contraction tops up the last 20%
When does the AV valves close?
When there is higher pressure in the ventricles than in the atrium
What is isovolumetric contraction?
Contraction of the ventricles when there is no change in volume
Describe how the aortic valve opens
The aorta is an area of high pressure so there needs to be a build up of pressure in the ventircles via isovolumetric contraction. When pressure in ventrical exceeds that in aorta, the aortic valve will open.
Describe how the aortic valve closes
The backflow of blood means that the pressure in the aorta exceed that in the ventricle, causing the aortic valve shut.
What must come before an increase in ventricular pressure
Ventricular depolarisation must come before contraction.
What is diastole?
Period of relaxation (ventricular)
What is systole?
Period of contraction (ventricular) S for Stress (contract)
What is the average systolic and diastolic blood pressure in the aorta?
S -120mmHg, D - 80mmHg
