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Biological Sciences
Peter A.Bowler

e109 Monday 11/5/12 Cardiac output (volume/time i.e. ml/time)= stroke volume (mL/beat or contraction) x heart rate (contractions or beats/min) -Pressure vs. volume graph (circle one) that discusses stroke volume and how to find the stroke volume from that graph -Cardiac output may be modified by neural input -Fig 14.19: Out put from central nervous system a) Parasympathetic neurons :: slows neurons • Parasympathetic stimulation hyperpolarizes the membrane potential of the autorhythmic cell and slows depolarization, slowing down the heart rate • sendsACh neuron to cholinergic receptors of autorhythimc cells • effect: increase in K+ permeability, and a decrease in the Ca2+ permeability o being more permeable to potassium makes the cell more hyperpolarized o takes longer to reach threshold  changes the rhythm: fewer beats = slows heart rate • result: hyperpolarizes cell and decreases the rate of depolarization and decreases heart rate b) sympathetic neurons: increases heart rate • norepinephrine (?) binds to Beta- receptors of autorhythmic cells • increase in Na+ permeability and increase in Ca2+ permeability • Rate of depolarization increases = increased heart rate o reaches threshold faster • Sympathetic stimulation and epinephrine depolarize the autorhythmic cell and speed up the pacemaker potential, increasing the heart rate Beta blockers -an antagonist to norepinephrine at beta 1- adrenergic receptors (so will block increase in heart rate by sympathetic stimulation) “Starling” curve-the ventricles will contract more forcefully when start contraction more distended • Force (indicated by stroke volume (mL)—amount of blood able to be pumped out) vs. stretch (indicated by ventricular end-diastolic volume in mL) • more blood in ventricle prior to contraction leads the heart to stretch more Skeletal muscle • amount of force that can be generated by the skeletal muscle is a function of sarcomere length • Tension is a direct relationship between the number of crossbridges Fig 14.20: Cardiac muscle -cardiac muscles undergo different length changes b/c of differences in geometry of the sarcomere—generates much larger range in maximal force Fig 14.22 Cardiac output is a function of heart rate and stroke volume -Heart rate is determined by rate of depolarization in authorhythmic cells a) increased b/c of sympathetic input and epinephrine b) de
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