Physiology: Chapter 14- Cardiac Action Potentials and Cardiovascular Overview
The resting membrane potential is ________ for skeletal muscle and ________ for contractile myocardium. It is ________ for autorhythmic myocardium.
-70 mV, -90 mV, unstable pacemaker potential (usually starts at -60 mV)
The rising phase of the action potential is a result of ________ for skeletal muscle, ________ for contractile myocardium, and ________ for autorhythmic myocardium.
Na+ entry, Na+ entry, Ca2+ entry
which ions moving in what directions cause the depolarization and repolarization phases of a neuronal action potential?
Na+ influx causes neuronal depolarization, and K+ efflux causes neuronal repolarization
The rapid depolarization phase of the action potentials of myocardial contractile cells is due to which ion(s)?
Na+ only
Police Captain Jeffers has and ejection fraction( SV divided by EDV) of only 25%. His stroke volume is 40 mL/ beat, and his heart rate is 100 beats/min. What are his EDV, ESV,and CO?
SV/EDV=.25 if SV=40mL, EDV=160 mL. SV=EDV-ESV, so ESV =120mL. CO=HR*SV=4 L/min
what prevents electrical signals from passing through the connective tissue in the heart?
connective tissue is not excitable and is therefore unable to conduct action potentials
Autorhythmic cells
are also called pacemakers because they set the rate of the heartbeat.
In an expt, the vagus nerve, which carries parasympathetic signals to the heart, was cut. The investigators noticed that heart rate increased. What can you conclude about the vagal neurons that innervate the heart?
cutting the vagus nerve increased heart rate, so parasympathetic fibers in the nerve must slow the heart rate
The flattening of the action potentials of myocardial contractile cells, called the plateau phase, is due to a combination of ________ K+ permeability and ________ Ca2+ permeability.
decreasing, increasing
The AV node is important because it
delays the transmission of the electrical impulses to the ventricles in order for the atria to finish contracting.
The purpose of having valves in the cardiovascular system is to
ensure that blood flows in one direction.
what happens to the action potential of a myocardial auto rhythmic cell if tetrodotoxin which blocks voltage-gated Na+ channels, is applied to the cell?
if tetrodotoxin is applied, nothing will happen because there are no voltage-gated Na+ channels in the cell
what does increasing K+ permeability do to the membrane potential of the cell?
increasing K+ permeability hyper polarizes the membrane potential
The action potentials of myocardial autorhythmic cells, are due to a combination of increasing Ca2+ ________ and decreasing K+________.
influx, eflux
the specialized cell junctions between myocardial cells are called____. These areas contain____that allow rapid conduction of electrical signals.
intercalated discs gap junctions
Cell junctions in contractile cells are called ________, which consist of two components: ________ and ________.
intercalated disks, desmosomes, gap junctions
A new cardiac drug called ivabradine selectively blocks If channels in the heart. what effect would it have on heart rate and for what medical condition might it be used?
ivabradine slows heart rate and is used to lower abnormally high heart rates
blood is recirculated instead of consumed.
microscopic vessels in which blood exchanges material with the interstitial fluid.
The importance of the plateau phase of the action potential of myocardial cells is in
preventing tetanus.
what is the function of the AV valves? what happens to blood flow if one of these valves fails?
the AV valves prevent backward flow of blood. If one fails, blood leaks back into the atrium
During Atrial filling, is pressure in the atrium higher or lower than pressure in the venue cavae?
the atrium has lower pressure than venae cavae
Name two functions of the AV node. What is the purpose of AV node delay?
the av node conducts action potentials from atria to ventricles. it also slows down the speed at which those action potentials are conducted, allowing atrial contraction to end before ventricular contraction begins
The term myogenic indicates that the heart muscle is the source of
the electrical signal that triggers heart contraction.
Occasionally an ectopic pacemaker develops in part of the heart's conducting system. What happens to heart rate if an ectopic atrial pacemaker depolarizes at a rate of 120 times per minute?
the fastest pacemaker sets the heart rate, so the heart rate increases to 120 beats/min
explain why contractions in cardiac muscle can't sum or exhibit tetanus
the long refractory period prevents a new action potential until the heart muscle has relaxed
What are If channels responsible for in cardiac autorhythmic cells?
the pacemaker potential
at the molecular level, what is happening during the refractory period in neurons and muscle fibers?
the refractory period represents the time required for the Na+ channel gates to reset (activation gate closes, inactivation gate opens)
why does ventricular pressure shoot up suddenly at point C...review wiggers diagram
ventricular pressure shoots up when the ventricles contract on a fixed volume of blood
calculate cardiac output is stroke volume is 65mL/beat and heart rate is 80beats/min
5200 mL/min or 5.2 L/min
a person has a total blood volume of 5 L. of this total, assume that 4 L is contained in the systemic circulation and 1 L is in the pulmonary circulation. If the person has a cardiac output of 5 L/min, how long will it take ofr a drop of blood leaving the left ventricle to return to the left ventricle and for a drop of blood to go from the right ventricle to the left ventricle?
85 mL
Why does blood flow through the cardiovascular system?
Because the heart establishes a pressure gradient
As blood flows away from the heart, how does overall blood pressure in vessels change? Why?
Blood pressure decreases, because of the effects of friction between the vessel walls and the moving blood.
In a cardiac autorhythmic cell, which ion is responsible for the increase in membrane potential from threshold during an action potential?
Ca+2
Which cells act as the heart's pacemaker? Why are they the pacemaker cells?
Cells of the SA node are the usual pacemaker, because they are autorhythmic cells and set the pace of the heart rate.
What is the role of heart valves?
Heart valves ensure one-way flow of blood through the heart chambers.
Distinguish: end-systolic volume and end-diastolic volume sympathetic and parasympathetic control of heart rate diastole and systole systemic and pulmonary circulation AV node and SA node
ESV: volume of blood in ventricle at end of contraction, EDV: volume of blood in the ventricle at beginning of contraction sympathetic: increases heart rate, parasympathetic: decreases heart rate Diastole: relaxation, Systole: contraction Pulmonary: goes to lungs, Systemic: goes to body AV node: transmits signals from atria to ventricles, SA node: is the atrial pacemaker
If channels are permeable to
Na+ and K+
Lidocaine is a molecule that blocks the action of voltage-gated cardiac Na+ channels. what happens to the action potential of a myocardial contractile cell if lidocaine is applied to the cell?
If cardiac Na+ channels are completely blocked with lidocaine, the cell will not depolarize and therefore will not contract. partial blockade will decrease electrical conduction
In skeletal muscle cells, action potentials cause the release of calcium from the SR by directly opening SR voltage-gated calcium channels. What causes the release of calcium from the SR in cardiac muscle cells?
Influx of extracellular calcium ions opens ryanodine receptors allowing Ca2+ to flow out of the SR.
What is an advantage to the longer duration of cardiac action potential compared to the skeletal muscle action potential?
The longer duration prevents tetanic contraction, which ensures that the heart chambers will relax and refill with blood before the next contraction.
In the 16th century, William Harvey discovered evidence that
blood is recirculated instead of consumed.
During the plateau phase of the action potentials of myocardial contractile cells, which ion(s), including those at decreased levels, is/are crossing the membrane?
both Ca2+ and K+
Most of the oxygen exiting the blood and entering the tissues does so from the ________.
capillaries
Compare and contrast the structure of a cardiac muscle cell with that of a skeletal muscle cell. What unique properties of cardiac muscle are essential to its function?
cardiac muscle has strong cell-to-cell junctions, gap junctions for electrical conduction, and the modification of some muscle cells into auto rhythmic cells
Arteries are most accurately defined as blood vessels that ________.
carry blood away from the heart
Along with nutrients, hormones, water, and gases, the cardiovascular system also transports _________
cellular waste immune cells heat
Consider three blood vessel segments of equivalent length and diameter: vessels A, B, and C. Pressure at the beginning of each segment is as follows: A) P = 100 mmHg; B) P = 80 mmHg; C) P = 60 mmHg. Pressure at the end of each segment is as follows: A) P = 70 mmHg; B) P = 50 mmHg; C) P = 30 mmHg. Which vessel has the greatest blood flow through the described segment?
flow rate is the same in all levels
The fibrous skeleton of the heart is important because it
forces electrical activity to be conducted through the atrioventricular node.
Why does the pressure in the arteries and arterioles fall as the blood moves away from the heart?
friction causes a loss of energy
The depolarization of the pacemaker action potential spreads to adjacent cells through
gap junctions
what is the proper term for each of the following? number of heart contractions per minute volume of blood in the ventricle before the heart contracts volume of blood that enters the aorta with each contraction volume of blood that leaves the heart in 1 minute volume of blood in the entire body
heart rate end-diastolic volume stroke volume cardiac output blood volume
The driving force for blood flow is a(n) ________ gradient.
pressure
the primary factor causing blood to flow through the body is a _____ gradient. In humans, the value of this gradient is highest at the ____and in the ____. It is lowest in the ___. In a system in which fluid is flowing, pressure decreases over distance because of ____.
pressure left ventricle aorta right atrium friction
Compare the receptors and channels involved in cardiac EC coupling to those found in skeletal muscle EC coupling.
skeletal muscle L-type Ca+2 channels are mechanically linked to SR RyR C+2 release channels. Myocardial L-type Ca+2 channels open to allow Ca+2 into the cell. In both muscles, sarcolemma Ca+2 channels are associated with RyR Ca+2 release channels on the SR
Calcium ions are removed from the sarcoplasm of the cardiac cell by the action of the sarcoplasmic reticulum (SR) Ca2+-ATPase pump and which other mechanism
sodium-calcium exchanger on the sarcolemma
Calcium ions are removed from the sarcoplasm of the cardiac cell by the action of the sarcoplasmic reticulum (SR) Ca2+-ATPase pump and which other mechanism?
sodium-calcium exchanger on the sarcolemma
The primary function of the cardiovascular system is to
transport material to and from all parts of the body.
a cardiovascular system has what three major components?
tubes (vessels) fluid (blood) pump (heart)
At an intercalated disc,
two cardiac muscle cells are connected by gap junctions.
Myocardial cells can generate action potentials spontaneously because they have
unstable ion channels
Where is the SA node located
upper right atrium
Which blood vessels have the lowest blood pressure?
veins
Which blood vessels return blood to the heart?
veins
which chamber-atrium or ventricle- has higher pressure during the following phases of the cardiac cycle? ventricular ejection isovolumic ventricular relaxation atrial and ventricular diastole isovolumic ventricular contraction
ventricle ventricle atrium ventricle