(B) DPHY Chapter 9 & 10: Heart Muscle & Rhythmic Excitation

which type of venous wave is caused by atrial contraction. Ordinarily, the right atrial pressure increases 4 to 6 mm Hg during atrial contraction, and the left atrial pressure increases about 7 to 8 mm Hg.

a-wave

Effect on the cardiac output curve of different degrees of sympa- thetic or parasympathetic stimulation.

Curves show relationship between right atrial pressure at the input of the heart and cardiac output (CO, ↑rate and force) into aorta (also similar to the ventricular function curve above).

6. diastole? sistole?

diastole - period of relaxation during which the heart fills with blood -followed by a period of contraction called systole.

10. How does one calculate stroke volume in terms of the difference between systolic and diastolic volume?

end-diastolic pressure (110-120 mL) - stroke volume output (70 mL) = end-systolic volume (40-50 mL)

9. What is the magnitude of the end diastolic volume? Of the end systolic volume?

end-diastolic volume - During diastole, normal filling of the ventricles increases the volume of each ventricle to about 110 to 120 mL. end systolic volume - The remaining volume in each ventricle after stroke volume is ejected, about 40 to 50 mL, is called the end-systolic volume. *When the heart contracts strongly, the end-systolic volume can be decreased to as little as 10 to 20 mL. Conversely, when large amounts of blood flow into the ventricles during diastole, the ventricular end- diastolic volumes can become as great as 150 to 180 milliliters in the healthy heart. By both increasing the end-diastolic volume and decreasing the end-systolic volume, the stroke volume output can be increased to more than double normal.

most important heart sounds

first and second heart sound -av closure -valve closure

What produces the second heart sound? What event produces the first heart sound?

first heart sound - When the ventricles contract, one first hears a sound caused by closure of the A-V valves. The vibration is low in pitch and relatively long-lasting. second heart sound - When the aortic and pulmonary valves close at the end of systole, one hears a rapid snap because these valves close rapidly, and the surroundings vibrate for a short period.

Isovolumic Relaxation

ventricle starts to relax but doesn't change its volume

What happens when diastolic ventricular volume are increased?

ventricular diastolic pressure increases

15. Describe the effects of sympathetic and parasympathetic nerve stimulation on cardiac function.

...

Volume of blood pumped by the heart is regulated in two ways

(1) intrinsic mechanism responsive to changes in volume of blood in heart and (2) the autonomic nervous system.

t/f The refractory period of atrial muscle is much shorter than that for the ventricles

(about 0.15 second for the atria compared with 0.25 to 0.30 second for the ventricles).

***Chapter 10

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2. What is the approximate inherent rate of the S-A node, the A-V node in the ventricular muscle?

-SA node - normal rate of the sinus node of 70 to 80 times per minute. -A-V nodal fibers, when not stimulated from some outside source, discharge at an intrinsic rhyth- mical rate of 40 to 60 times per minute,

6. Describe the effects of the autonomic nervous system on cardiac conduction and rhythmicity.

-Stimulation of the parasympathetic nerves to the heart (the vagi) causes the hormone acetylcholine to be released at the vagal endings. This hormone has two major effects on the heart. First, it decreases the rate of rhythm of the sinus node, and second, it decreases the excitability of the A-V junctional fibers between the atrial musculature and the A-V node, thereby slowing transmission of the cardiac impulse into the ventricles. -sympathetic stimulation causes essentially the opposite effects on the heart to those caused by vagal stimulation, as follows: First, it increases the rate of sinus nodal discharge. Second, it increases the rate of conduction as well as the level of excitability in all portions of the heart. Third, it increases greatly the force of contraction of all the cardiac musculature, both atrial and ventricular. (Stimulation of the sympathetic nerves releases the hormone norepi- nephrine at the sympathetic nerve endings.)

7. What are the central venous pressure waves (i.e. right atrial pressure changes) in each cardiac cycle?

-a-wave is caused by atrial contraction. Ordinarily, the right atrial pressure increases 4 to 6 mm Hg during atrial contraction, and the left atrial pressure increases about 7 to 8 mm Hg. -c wave occurs when the ventricles begin to contract; it is caused partly by slight backflow of blood into the atria at the onset of ventricular contraction but mainly by bulging of the A-V valves backward toward the atria because of increasing pressure in the ventricles. -v wave occurs toward the end of ventricular contraction; it results from slow flow of blood into the atria from the veins while the A-V valves are closed during ventricular contraction. Then, when ventricular contraction is over, the A-V valves open, allowing this stored atrial blood to flow rapidly into the ventricles and causing the v wave to disappear.

which type of venous wave occurs when the ventricles begin to contract; it is caused partly by slight backflow of blood into the atria at the onset of ventricular contraction but mainly by bulging of the A-V valves backward toward the atria because of increasing pressure in the ventricles.

-c wave

two mechanisms for calcium removal after depolarization

-calcium pump in sarcoplasmic reticulum -sodium/calcium exchanger in cell membrane of cardiac fiber (coupled with sodium/potassium ATPase; mechanism is secondary counter-transport where potential is generated by one that runs the other)

which type of innervation has a greater effect on the heart

-effect of parasympathetic is lower than sympathetic -sympathetic is more because of denser innervation

1. Why is the heart regarded as a functional syncytium?

-group of cardiac cells known as heart functions as unit -2 different syncytiums in heart: atrial and ventricular

compare the types of innervation in heart

-parasympathetic innervation affects mainly the aorta and the rate of contraction (mainly depresses chronotropic action of heart) -sympathetic affects the rate of contraction as well as the force (chronotropic and inotropic)

occurs toward the end of ventricular contraction; it results from slow flow of blood into the atria from the veins while the A-V valves are closed during ventricular contraction. Then, when ventricular contraction is over, the A-V valves open, allowing this stored atrial blood to flow rapidly into the ventricles and causing the v wave to disappear.

-v wave

The rate of blood flow into heart from vein is called _ _ and it determines _ _ _...

-venous return -the amount of blood pumped by the heart.

13. What is Starling's Law of the heart for the Frank-Starling relationship?

...

14. How does one calculate cardiac output in terms of heart rate and stroke volume? What happens to cardiac output as right atrial pressure increases?

...

what is the order of the venous waves

A C V

4. What are ectopic beats in terms of the heart rate, what produces them?

A pacemaker elsewhere than the sinus node is called an "ectopic" pacemaker. An ectopic pacemaker causes an abnormal sequence of contraction of the different parts of the heart and can cause significant debility of heart pumping. could occur in the A-V node or purkinje fibers

What event produces the incisura or dicrotic notch in the aortic pressure curve?

A so-called incisura occurs in the aortic pressure curve when the aortic valve closes. This is caused by a short period of backward flow of blood immediately before closure of the valve, followed by sudden cessation of the backflow.

The pressure that the ventricle must generate in order to eject blood out of the heart. For the left ventricle afterload is a function of the aortic pressure.

Afterload:

Right and left ventricular volume output curves

Approximate normal right and left ventricular volume output curves for the normal resting human heart as extrapolated from data obtained in dogs and data from human beings. • As the right and left atrial pressures rise, respective ventricular outputs/min also increases

sympathetic and parasympathetic innervation of hear

Cardiac sympathetic and parasympathetic nerves. (The vagus nerves to the heart are parasympathetic nerves. Cardiac sympathetic and parasympathetic (called vagus in heart) nerves sympathetic - fight or flight parasympathetic - calming, restorative stimulus

cardiac output and arterial pressure

Constancy of cardiac output up to a pressure level of 160 mm Hg. Only when the arterial pressure rises above this normal limit does the increasing pressure load cause the cardiac output to fall significantly.

definition of cardiac cycle

Event from beginning of one heartbeat to the beginning of the next

Events of the cardiac cycle for left ventricular function, showing changes in left atrial pressure, left ventricular pressure, aortic pressure, ventricular volume, the electrocardiogram, and the phonocardiogram.

Events of the cardiac cycle for left ventricular function, showing changes in left atrial pressure, left ventricular pressure, aortic pressure, ventricular volume, the electrocardiogram, and the phonocardiogram. Six curves shown: • Electrocardiogram with P, Q, R, S, and T waves: - These are electrical voltages generated by the heart and recorded from the surface of the body (see below for detail). • Phenocardiogram: - Recording of sounds produced by heart as it pumps- mainly by heart valve closure.

Very strong excitatory signals can produce premature contractions

Force of ventricular heart muscle contraction, showing also duration of the refractory period and relative refractory period, plus the effect of premature contraction. Note that premature contractions do not cause wave summation, as occurs in skeletal muscle.

3. Why does the heart remain depolarized during the plateau period?

In cardiac muscle, the action potential is caused by opening of two types of channels: (1) the same fast sodium channels as those in skeletal muscle and (2) another entirely different population of slow calcium channels, which are also called calcium-sodium channels. This second population of channels differs from the fast sodium channels in that they are slower to open and, even more important, remain open for several tenths of a second. During this time, a large quantity of both calcium and sodium ions flows through these channels to the interior of the cardiac muscle fiber, and this maintains a prolonged period of depolarization, causing the plateau in the action potential. Further, the calcium ions that enter during this plateau phase activate the muscle contractile process, while the calcium ions that cause skeletal muscle con- traction are derived from the intracellular sarcoplasmic reticulum.

ventricular stroke work output as a function of left and right mean atrial pressures.

Left and right ventricular function curves recorded from dogs, depicting ventricular stroke work output as a function of left and right mean atrial pressures.

Organization of the A-V node.

Organization of the A-V node. The numbers represent the interval of time from the origin of the impulse in the sinus node. The values have been extrapolated to human beings. The internodal and interatrial pathways transmit impulses in the atrium. - These pathways subsequently carry impulses to the AV node. • The AV nodes delays impulses from the atria to the ventricles and this allows atria to empty contents into ventricles before ventricular contraction occurs.

anatomy of heart valve

Mitral and aortic valves (the left ventricular valves) -note presence of papillary muscle

5. What mechanical event in the cardiac cycle immediately precedes the QRS complex?

P wave is caused by spread of depolarization through the atria, and this is followed by atrial contraction, which causes a slight rise in the atrial pressure curve immediately after the electrocardiographic P wave.

End-diastolic pressure when ventricle has become filled. Preload is affected by venous blood pressure and the rate of venous return. These are affected by venous tone and volume of circulating blood.

Preload

preload and afterload

Preload: End-diastolic pressure when ventricle has become filled. Preload is affected by venous blood pressure and the rate of venous return. These are affected by venous tone and volume of circulating blood. Afterload: The pressure that the ventricle must generate in order to eject blood out of the heart. For the left ventricle afterload is a function of the aortic pressure.

AP of cardiac muscle

Rhythmical action potentials (in millivolts) from a Purkinje fiber and from a ventricular muscle fiber, recorded by means of microelectrodes.

Rhythmical discharge of a sinus nodal Fiber

Rhythmical discharge of a sinus nodal fiber. Also, the sinus nodal action potential is compared with that of a ventricular muscle fiber. Sinus node controls rate of beat of entire heart. - At resting MP there is slow leak of Na into fiber - Between AP, resting MP gradually rises due to the slow Na leak till -40 mV - Then, Na-Ca channels get activated allowing entry of both ions, specially Ca to cause AP - Then, K channels open and K ions escape, returning MP to resting potential.... cycle restarts.

Heart Conduction System

Sinus node, and the Purkinje system of the heart, showing also the A-V node, atrial internodal pathways, and ventricular bundle branches. - Sinus node(sinoatrial node): initiates cardiac impulse - Internodal pathway: conducts impulse from sinus node to AV node - AV node: delays impulses from atria to ventricles - AV bundle: conducts impulse from AV node to venrticles - Right and left bundles of Purkinje fibers: conduct impulse to all parts of the ventricles

structutre of heart

Structure of the heart, and course of blood flow through the heart chambers and heart valves.

2. What is the all-or-nothing principle as applied to the heart?

The all-or-none law is the principle that the strength by which a nerve or muscle fiber responds to a stimulus is not dependent on the strength of the stimulus. If the stimulus is any strength above threshold, the nerve or muscle fiber will give a complete response or otherwise no response at all. An induction shock produces a contraction or fails to do so according to its strength; if it does so at all, it produces the greatest contraction that can be produced by any strength of stimulus in the condition of the muscle at the time." This relationship holds only for the unit of tissue; for the heart the unit is the entire auricles or the entire ventricles. the auricles or ventricles behave as a single unit, so that an adequate stimulus normally produces a full contraction of either the auricles or ventricles.

Intrinsic regulation: the Frank-Starling mechanism

The greater the volume of blood entering the heart during diastole (end-diastolic volume), the greater the volume of blood ejected during systolic contraction (stroke volume) (ie., within the physiological limits of the heart).

3. Where is the conduction velocity of the wave of depolarization slowest in the heart? Where is it most rapid?

The numbers on the figure represent the intervals of time, in fractions of a second, that lapse between the origin of the cardiac impulse in the sinus node and its appear- ance at each respective point in the heart. Note that the impulse spreads at moderate velocity through the atria but is delayed more than 0.1 second in the A-V nodal region before appearing in the ventricular septal A-V bundle. Once it has entered this bundle, it spreads very rapidly through the Purkinje fibers to the entire endocardial surfaces of the ventricles. Then the impulse once again spreads slightly less rapidly through the ventricular muscle to the epicardial surfaces.

What is Starling's Law of the heart for the Frank-Starling (FS) relationship?

Within physiologic limits, the heart pumps all of the blood that comes to it without allowing excessive damming of blood in the veins.

4. What does the term absolute refactory period of the heart mean in electrical terms? What does the term, relative refractory period mean? When in the ECG is the heart relatively refractory?

absolute refractory period - interval of time, as shown to the left in Figure 9-4, during which a normal cardiac impulse cannot re-excite an already excited area of cardiac muscle. The normal refractory period of the ventricle is 0.25 to 0.30 second which is about the duration of the prolonged plateau action potential. relative refractory period - relative refractory period of about 0.05 second during which the muscle is more difficult than normal to excite but nevertheless CAN be excited by a very strong excitatory signal, as demonstrated by the early "premature" contraction

2 different syncytiums in heart

atrial and ventricular

When are all values closed? When are all valves open?

atrial systole - SL valves closed and AV valves open ventricular systole - SL valves open and AV valves closed

5. What does a pulse rate of 50 beats a minute in a non-athlete suggest?

bradychardia - in the context of adult medicine, is the resting heart rate of under 60 beats per minute, though it is seldom symptomatic until the rate drops below 50 beats/min. It may cause cardiac arrest in some patients, because those with bradycardia may not be pumping enough oxygen to their hearts. It sometimes results in fainting, shortness of breath, and if severe enough, death

principle ion in action potential of cardiac muscle

calcium (sodium is present but not as big a role as calcium)

systole

contraction of ventricle

Isovolumic contraction

contraction that does not show a change in volume

what enables cardiac cells to excite surrounding cardiac cells

gap junctions at intercalated discs

12. What is a prolapsed valve? What are its functional consequences? Clinical consequences? When should you give patients with prolapsed mitral valves antibiotic coverage?

in vanes of A-V node; chordae tendineae. The papillary muscles contract when the ventricular walls contract, but contrary to what might be expected, they do not help the valves to close. Instead, they pull the vanes of the valves inward toward the ventricles to prevent their bulging too far backward toward the atria during ventricular contraction. If a chorda tendinea becomes ruptured or if one of the papillary muscles becomes paralyzed, the valve bulges far backward during ven- tricular contraction, sometimes so far that it leaks severely and results in severe or even lethal cardiac incapacity.

When does the heart undergo isovolumic contraction in terms of the cardiac cycle? What is isovolumic relaxation of the heart and when does it occur?

isovolumic contraction - during this period, contraction is occurring in the ventricles, but there is no emptying; aka isometric contraction, meaning that tension is increasing in the muscle but little or no shortening of the muscle fibers is occurring. isovolumic relaxation - At the end of systole, ventricular relaxation begins suddenly, allow- ing both the right and left intraventricular pressures to decrease rapidly. The elevated pressures in the dis- tended large arteries that have just been filled with blood from the contracted ventricles immediately push blood back toward the ventricles, which snaps the aortic and pulmonary valves closed. For another 0.03 to 0.06 second, the ventricular muscle continues to relax, even though the ventricular volume does not change, giving rise to the period of isovolumic or iso- metric relaxation. During this period, the intraventricular pressures decrease rapidly back to their low diastolic levels. Then the A-V valves open to begin a new cycle of ventricular pumping.

11. What determines the magnitude of the stroke volume? What is the size of the stroke volume normally?

magnitude of stroke volume is determined by magnitude of end-diastolic pressure and the strength of the contraction (By both increasing the end-diastolic volume and decreasing the end-systolic volume, the stroke volume output can be increased to more than double normal.)

Ejection

period of ejection into aorta -beginning of blood pressure -pressure will be more than 80 mm Hg or valve will not open

what ion contributes to repolarization in cardiac muscle (as well as cardiac muscle)

potassium

location, function, and significance of papillary muscles

regulatory factor that keeps valve functioning tightly - keeps valve from bulging back

diastole

relaxation of ventricle

compare the stimuli from sympathetic and parasympathetic nervous systems

sympathetic - fight or flight parasympathetic - calming, restorative stimulus

t/f Thus, the atria act as primer pumps for the ventricles, and the ventricles in turn provide the major source of power for moving blood through the body's vascular system.

t

t/f the A-V valves are supported by the chordae tendineae, which is not true for the semilunar valves.

t

t/f 80 per cent of the blood flows directly through the atria into the ventricles even before the atria contract. Then, atrial contraction usually causes an additional 20 per cent filling of the ventricles.

t - -atria serves as primer pumps that increase the ventricular pumping effectiveness as much as 20 percent.

As the cardiac RP lasts throughout the contraction (ie., takes same period), it prevents the myocardium from getting tetanized by repeated stimulation.

tentanization not observed in cardiac muscle because of overlap

• Stretching the heart muscle with extra blood causes the muscle to contract with increased force because...

the actin and myosin filaments are brought to a more optimal degree of interdigitation for force generation. This ability of stretched muscle, up to an optimum length, to contract with increased force is characteristic of all striated muscle.

1. What membrane events produce the slow depolarization that occurs in the sinus node during diastolic filling of the ventricles?

the resting potential of the sinus node is much lower (in comparison with -85 to -90 millivolts for the ventricular muscle fiber) therefore the fast Ca channels have already become "inactivated"; the cause of this lesser negativity is that the cell membranes of the sinus fibers are naturally leaky to sodium and calcium ions, and positive charges of the entering sodium and calcium ions neutralize much of the intracellular negativity. only the slow sodium-calcium channels can open (i.e., can become "activated") and thereby cause the action potential. As a result, the atrial nodal action potential is slower to develop than the action potential of the ventricular muscle. Also, after the action potential does occur, return of the potential to its negative state occurs slowly as well, rather than the abrupt return that occurs for the ventricular fiber.

what nerve is mainly responsible for the parasympathetic innervation in the heart

vagus

Mechanisms of excitation-contraction coupling and relaxation in cardiac muscle.

• Diffusion of calcium into myofibrils promotes muscle contraction by similar mechanisms as in SKM. AP • The T tubules in cardiac muscle are 25x bigger, enabling greater Ca release. • Also, cardiac muscle contraction is highly dependent on EC calcium influx. • Ca is removed during relaxation by Ca pump (into SR) and by Na/Ca exchanger in CM (linked to Na-K ATPase).