Unformatted text preview: Action Potential at SA Node Ca ion influx brings it up to 40mV (threshhold) Autonomic Tone Affecting heart Rate Dual innervation sympathetic and parasympathetic In healthy, resting individuals, parasympathetic Acetylcholine is released If parasympathetic effects dominate activity increases, the heart rate declines If sympathetic activity increases, the heart rate increases Autonomic Tone Affecting Heart Rate Effects on SA Node The sympathetic and parasympathetic divisions alter heart rate by changing the ionic permeabilities of cells in the conducting system Acetylcholine (released by parasympathetic) opens chemically gated K+ channels (positive ions leak out) this slows the rate of spontaneous depolarization and extends the duration of repolarization so the heart rate slows Norepinephrine (sympathetic) opens sodiumcalcium channels; this influx of positively charged ions increases the rate of depolarization and shortens the period of repolarization so the SA node reaches threshold faster and Action Potential in Cardiac Muscle See pg. 701 + Rapid depolarization from sodium(Na ) influx Plateau from Ca ion entry + + Repolarization from K ion loss Skeletal vs. Cardiac Muscle Action Potentials Skeletal muscle Action potential and contraction are much shorter duration than cardiac muscle Action Potential Inhibition ? Postsynaptic potential Inhibition makes it harder to contract Arrhythmias Problems with electrical conduction Flutter Fibrillation Tachycardia Bradycardia Arrhythmias Flutter 200300 beats/min Beats are coordinated Can turn into fibrillation Arrhythmias Fibrillation 200300 beats/min Beats are uncoordinated Can arise from flutter Arrhythmias Tachycardia Greater than 100 beats/min Arrhythmias Bradycardia Less than 60 beats/min Heart Murmurs Abnormal heart sounds due to abnormal valve closure Pressure and Volume Changes During Cardiac Cycle Step 1 Ventricular Filling: Passive Atria and Ventricles in diastole quiescent period; AV valves are open Semilunar valves are closed Ventricles have passive filling over 70% get filled Pressure and Volume changes During Cardiac Cycle Step 1 Atrial Systole Atrial systole Atria contract and deliver remaining 2030% of blood to ventricles Atrial pressure is greater than ventricular AV valves are open End diastolic volume volume of blood in pressure ventricles at the end of ventricular diastole (which is when atrial systole ends) EDV is maximum amount of blood in ventricles Pressure and Volume Changes During Cardiac Cycle Step 2 Ventricular Systole Ventricles contract (systole) Increase in ventricular pressure above atrial AV valves close First heart sound is lub when AV valves close Isovolumetric contraction First part of ventricular systole; all valves are closed; pressure increases, but volume doesn't change pressure Pressure and Volume changes Step 2B Ventricuolar Systole Ventricles still contracting Once ventricular pressure rises above the pressure in the arteries, the semilunar valves open and blood flows out of the ventricles Semilunar valves open Blood is ejected from ventricles Pressure and Volume changes `Step 5 Pressure in aorta and pulmonary trunk increase Semilunar valves close second sound (dub) Isovolumetric relaxation all valves closed; volume stays the same, but pressure in ventricles is decreasing Pressure and Volume changes Step 6 Atria are filling and as pressure increase in the atria, the AV vavles open again Ventricular filling begins again Blood Pressure If blood vessels are constricted, total peripheral resistance is increases and blood pressure is increased If vessels are dilated, total peripheral resistance is decreased and pressure is decreased Stroke Volume Amount of blood ejected from ventricles per beat Heart see pg 705, 707, 708 ...
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- Spring '09
- Cardiology, heart rate, volume changes