bio 235 exam 3 study guide Questions and
Answers Verified by Experts
why is the SA node called the pacemaker and what would happen to heart rate if the SA node
were destroyed? it is the action potential of the autorhythmic cells in the SA node that
starts the heartbeat. In other words the SA node sets the pace of the heartbeat. if the SA node is
destroyed then the heartbeat will slow down and follow the next fastest pacemaker which would
be the AV node.
in the action potential of the SA node, what ionic events occur during the rising face? Falling
phase? The slow drift towards threshold? Figure 14-12 Rising phase = at -40mv, Ca
channels open and Ca enters cell causing the repolarization.
falling phase = Ca channel closed and K channels open causing efflux and K and repolarization.
(no hyperpolarization)
Slow drift towards threshold = at -60mV, K channels close and funny channels open allowing
influx of Na until membrane potential reaches -40mV.
,what do the sympathetic and parasympathetic nervous systems do to the heart rate?
parasympathetic nervous system slows the heart rate.
sympathetic nervous system increases the heart rate.
what does sympathetic and parasympathetic activity due to the ionic permeability of sodium
potassium and calcium? Figure 14-19 sympathetic control - increases sodium and
calcium influx which causes a cell to reach threshold faster and send more rapid action potential
which increases the rate of depolarization and increase the heart rate.
parasympathetic control - decrease calcium influx and increase potassium efflux causing the
pacemaker to be at a more negative value which will require more time for calcium to depolarize
the cell; Thus, causing the heart to slow.
what ensures that adjacent muscles contract at the same time? desmosomes and GAP
Junctions of intercalated discs
explain what occurs during the P wave, PR segment, QRS complex and T wave of an EKG.
Figure 14 - 15 P wave = atrial depolarization
PR segment = conduction through AV node and AV bundle
QRS complex = ventricular depolarization followed by contraction of the ventricles
, T wave = ventricular repolarization
give the definition of diastole and systole Systole = The time interval between S1 and S2
when the ventricles contract
Diastole = The time interval between S2 and the next S1 in which the ventricles relax.
S1 = AV node closes and ventricles begin to contract
S2 = Semilunar valves closes and ventricles relax
what is meant by cardiac output and what two main factors determine cardiac output?
cardiac output is the volume of blood pumped by one ventricle in a given period of time.
heart rate and stroke volume determine cardiac output
Heart rate x Stroke volume = cardiac output
Answers Verified by Experts
why is the SA node called the pacemaker and what would happen to heart rate if the SA node
were destroyed? it is the action potential of the autorhythmic cells in the SA node that
starts the heartbeat. In other words the SA node sets the pace of the heartbeat. if the SA node is
destroyed then the heartbeat will slow down and follow the next fastest pacemaker which would
be the AV node.
in the action potential of the SA node, what ionic events occur during the rising face? Falling
phase? The slow drift towards threshold? Figure 14-12 Rising phase = at -40mv, Ca
channels open and Ca enters cell causing the repolarization.
falling phase = Ca channel closed and K channels open causing efflux and K and repolarization.
(no hyperpolarization)
Slow drift towards threshold = at -60mV, K channels close and funny channels open allowing
influx of Na until membrane potential reaches -40mV.
,what do the sympathetic and parasympathetic nervous systems do to the heart rate?
parasympathetic nervous system slows the heart rate.
sympathetic nervous system increases the heart rate.
what does sympathetic and parasympathetic activity due to the ionic permeability of sodium
potassium and calcium? Figure 14-19 sympathetic control - increases sodium and
calcium influx which causes a cell to reach threshold faster and send more rapid action potential
which increases the rate of depolarization and increase the heart rate.
parasympathetic control - decrease calcium influx and increase potassium efflux causing the
pacemaker to be at a more negative value which will require more time for calcium to depolarize
the cell; Thus, causing the heart to slow.
what ensures that adjacent muscles contract at the same time? desmosomes and GAP
Junctions of intercalated discs
explain what occurs during the P wave, PR segment, QRS complex and T wave of an EKG.
Figure 14 - 15 P wave = atrial depolarization
PR segment = conduction through AV node and AV bundle
QRS complex = ventricular depolarization followed by contraction of the ventricles
, T wave = ventricular repolarization
give the definition of diastole and systole Systole = The time interval between S1 and S2
when the ventricles contract
Diastole = The time interval between S2 and the next S1 in which the ventricles relax.
S1 = AV node closes and ventricles begin to contract
S2 = Semilunar valves closes and ventricles relax
what is meant by cardiac output and what two main factors determine cardiac output?
cardiac output is the volume of blood pumped by one ventricle in a given period of time.
heart rate and stroke volume determine cardiac output
Heart rate x Stroke volume = cardiac output
