BIO152 EXAM ONE

Heartbeat

- 100,000 beats per day - consists of a cycle of events; lasts about eight-tenths of a second

gap junctions

- action potentials generates by autorhythmic cells create waves of depolarization that spread to contractile cells via gap junctions

Semilunar Valves

- allow ejection of blood from the heart into the arteries but prevent back flow of blood into the ventricles - valves open when pressure in the contracted ventricles exceeds the pressure in the arteries - ventricles relax-blood flows back toward the heart. Back flow fills valve cusps-tightly close the semilunar valves

autorhythmic fibers:

- are self excitable - are pacemakers - form the conduction system of the heart

which of the following are true in reference to heart regulation

- at rest, parasympathetic stimulation predominates - sympathetic stimulation triggers the release of norepinephrine - the movement of limbs is monitored by proprioceptors - parasympathetic fibers travel via the vagus nerve

Ventricular Filling: Atrial Contraction

- atria contract, forcing the remaining blood into the ventricles - blood flows through both sides of the heart at the same time

Atrioventricular Valves

- atrioventricular valves - bicuspid, tricuspid - prevent blood flow from the ventricles back into the atria - How? contraction of papillary muscles tightening the chordae tendinae - prevents the valve cusps from everting

Pacemaker Potential in Autorhythmic Cells

- autorhythmic cells begin depolarizing due to a slow continuous influx of sodium, and a reduced efflux of potassium - as sodium ions enter the cell, the inner surface of the plasma membrane gradually becomes less negative, generating the pacemaker potential - note that the cell starts out at resting membrane potential(~ -60 mV), positive out, negative in - there is a slow, continuous movement of sodium inside the cell. The inner membrane gradually becomes less negative, depolarizing slowly, generating the pacemaker potential

Purkinje Fibers

- begin at the lower interventricular septum to the apex of the heart, then continue superiorly through the myocardium of the ventricles - the Purkinje fibers convey the action potentail to the contractile cells of the ventricle - action potentials, which spread from the autorhythmic cells of the intrinsic conduction system to the contractile cells are electrical events - subsequent contraction of the contractile cells is a mechanical event that causes a heartbeat

intrinsic conduction system

- cardiac autorhythmic cells in the intrinsic conduction system generate action potentials that spread in waves to all the cardiac contractile cells; this action causes a coordinated heart contraction; of all the cells in the body, only heart cells are able to contract on their own without stimulation from the nervous system

Bundle Branches

- convey the action potential down the interventricular septum

heart valves

- during the cardiac cycle, heart valves open and close in response to differences in blood pressure on their two sides - the heart valves: * pulmonary semilunar valve * aortic semilunar valve * left AV valve or Bicuspid valve or mitral valve * right AV valve or Tricuspid valve

the intercalated discs seen in cardiac myocytes

- have desmosomes which help to hold the muscle fibers together - have gap junctions which allow action potentials to conduct from one muscle fiber to the next

Action Potentials in Autorhythmic Cells

- here is an overview of the initiation of action potentials in an autorhythmic cell: 1. Pacemaker Potential + an autorhythmic cell has the unique ability to depolarize spontaneously, resulting in a pacemaker potential 2. Depolarization and Reversal of the Membrane Potential + once threshold is reached, an action potential is initiated, which begins with further depolarization and leads to reversal of the membrane potential 3. Repolarization + then repolarization occurs, returning the cell to its resting membrane potential + the cell cpontaneously begins to slowly depolarize again and the sequence is repeated

depolarization vs. repolarization

- if depolarization reaches threshold, the contractile cells, in turn, generate action potentials, first depolarizing then repolarizing; after depolarization, the cardiac myofibrils in contractile cells slide over each other resulting in muscle contraction; after repolarization these cells relax

stroke volume is increased by

- increased preload - decreased afterload - increased contractility

summary of cardiac action potential

- initiation of action potential in autorhythmic cells: 1. pacemaker potential due to influx of sodium and reduced efflux of potassium 2. depolarization and reversal of the membrane potential due to influx of calcium 3. repolarization due to efflux of potassium - initiation of action potential in contractile cells: 1. opening of voltage-regulated fast sodium channels triggered by entry of positive ions from adjacent cell: depolarization due to rapid influx of soidum 2. plateau produced by calcium influx balancing potassium efflux 3. repolarization due to efflux of potassium

Ventricular Systole: Contraction

- isovolumetric contraction: ventricles contract and intraventricular pressure rises, closing the AV valves. Briefly, ventricles are completely closed chambers

AV node

- located in the inferior interatrial septum - the action potential is delayed here briefly, while the atria contract, before being transmitted to the AV bundle

Internodal pathway

- located in the walls of the atria - links the SA node to the AV node - distributes the action potential to the contractile cells of the atria

SA node

- located in upper right atrium - initiates the depolarizing impulse which, in turn, generates an action potential that spreads throughout the atria to the AV node - sets the overall pace of the heartbeat

Ventricular Filling: Passive

- occurs during mid to late diastole, when the heart chambers are relaxed - blood flow passively into the atria, through open AV valves, and into the ventricles, where the pressure is lower

stroke volume is regulated by:

- preload - contractility of the individual ventricular muscle fibers - afterload or the pressure that must be exceeded before ejection of blood from the ventricles can occur

Contractile Cell Anatomy

- the cardiac contractile cell relies on the autorhythmic cell to generate an action potential and pass the impulse down the line before the cell can contract - like the autorhythmic cell, it has protein transport channels, but they are slightly different - gap junctions link autorhythmic and contractile cells, and link contractile cells with each other - notice the sarcoplasmic reticulum(SR), which is a storage site for calcium. Channels within the SR membrane allow calcium ions to be released within the cell - the myofilaments are the contractile units of the cardiac muscle cell

Heart and ECG Comparison

- the contraction of the ventricle begins at the apex of the heart and moves superiorly, forcing the blood upward toward the arteries. This is important because the large arteries are located superiorly. So blood has to be rung from the bottom of the heart up - correlation between heart electrical activity and an ECG wave tracing P wave: indicates atrial depolarization which is followed by atrial contraction QRS wave: represents ventricular depolarization which is followed by ventricular contraction T wave: represents ventricular repolarization which is followed by ventricular relaxation

histology summary

- the heart consists of four chamber: the right atrium, right ventricle, left atrium, and left ventricle - the right atrium receives oxygen-poor blood from the systemic veins; blood moves to the right ventricle and is pumped out the pulmonary arteries to the lungs

Intrinsic Conduction System summary

- the intrinsic conduction system of the heart initiates depolarization impulses - action potentials spread throughout the heart, causing coordinated heart contraction - an ECG wave tracing records the electrical activity of the heart

intrinsic conduction system introduction

- the intrinsic conduction system sets the basic rhythm of the beating heart - it consists of autorhythmic cardiac cells that initiate and distribute impulses(action potentials)

AV bundle

- the only electrical connection between the atria and the ventricles - allows the action potential to move from the interatrial septum to the interventricular septum, connecting the AV node to the Bundle Branches

which of the following are correct

- the walls of the ventricles are thicker because the ventricles pump blood under high pressure over great distances - the wall of the right ventricle is thinner than that of the left ventricle because the right side of the heart pumps blood a shorter distance at lower pressure - although the right side of the heart has a smaller workload, the right and left ventricle simultaneously eject the same amount of blood

Cardiac muscle cells

- there are two kinds of cell junctions and the intercalated discks - the desmosomes are anchoring junctions that hold adjacent cells together. When the muscle cell contracts, they pull on each other. If it wasn't for the desmosomes, the heart would literally pull itself apart in doing its job - the gap junctions allow the stimulating impulse to move across the heart from cell-to-cell so the heart beats as an entire unit. It each cardiac muscle cell were allowed to do its own thing the heart would be useless as a pump

Repolarization in Autorhythmic Cells

- this reversal of membrane potential triggers the openings the opening of potassium channels, resulting in potassium rapidly leaving the cell - potassium efflux produces repolarization, bringing the membrane potential back down to its resting level - membrane potential goes from +10 mV to resting membrane potential(-60 mV) - ionic pumps actively transport calcium back to the extracellular space during repolarization - Na+/K+ pumps also pump sodium out and potassium in

Operation of Heart Valves

- valves open and close in response to pressure changes as the heart contracts and relaxes(just like a whoopy cushion - insures one way movement through the heart

Ventricular Systole: Ejection

- ventricular ejection: rising ventricular pressure forces semilunar valves open. Blood is ejected from the heart into the aorta and pulmonary trunk

Depolarization in Autorhythmic Cells

- when the membrane potential gets to -40 millivolts, it has reached threshold for initiating an action potential. Fast calcium channels open and positively-charged calcium ions rush in - calcium influx produces the rapidly rising phase of the action potential(depolarization), which results in the reversal of membrane potential from negative to positive inside the cell - depolarization peaks at about +10 mV

autorhythmic cell anatomy

-embedded in the plasma membrane of an autorhythmic cell we see several protein channels that allow ions to move into or out of the cell These are crucial for generating an action potential: 1. sodium channels-allow sodium ions to enter the cell 2. fast calcium channels-allow calcium ions to enter the cell 3. potassium channels-allow potassium ions to leave the cell - the movement of ions affects the membrane potential(the voltage across the membrane) - the membrane potential is a result of the relative concentrations of ions along the inside and outside of the plasma membrane - if there are more positive ions outside the cell, then the inside of the cell is relatively negative, as shown - if there are more positive ions inside the cell, then the inside of the cell is relatively more positive - many transport channels are voltage-regulated; they open and close in response to specific voltage levels across the membrane - gap junction connects adjacent cardiac cells, this allows ions to pass between cells, allowing a ripple effect of initiating depolarization in one cell, and then another, and so on

Ion Movement Through Gap Junction

1. Depolarization - during depolarization in adjacent autorhythmic cells or contractile cells, positive ions move through gap junctions to adjacent contractile cells - this entry of positive ions creates a small voltage change, initiating depolarization - note that neurotransmitters are not involved as they are with the innervation of skeletal muscles

Depolarization in Contractile Cells

1. Depolarization - voltage change stimulates opening of voltage-regulated fast sodium channels - rapid influx of sodium results in depolarization and reversal of the membrane potential from negative inside the cell to positive. Recall that for the autorhythmic cell its the rapid influx of calcium and not sodium that causes depolarization - Summary of Depolarization: * at rest, contractile cells have a resting membrane potential of about -90 mV * neighboring cells(either autorhythmic or contractile cells) depolarize * gap junctions open and positive ions(Ca2+ and Na1+) move in to the contractile cells through gap junctions * a small voltage change(of about 5 mV to about -85 mV) occurs which initiates depolarization * voltage gated sodium channels in the membrane of the contractile cells open allowing sodium to move into the cell * this results in a reversal of charge(depolarization)(to about +25 mV) as sodium moves into the cell

Myocardial Thickness

1. atria walls - thin - deliver blood to the ventricles 2. ventricle walls - thicker - pump blood greater distances 3. right ventricle - thinner than left - pump blood into the lungs, nearby, offer very little resistance to blood flow 4. left ventricle walls - thicker - pump blood through the body, resistance to blood flow is greater

Heart - Fibrous Skeleton

1. dense connective tissue laid out in rings 2. heart valve attachment foundation 3. points of insertion for cardiac muscle bundles 4. prevents overstretching of the valves(not a sure thing because some people need valve replacements) 5. electrical insulator - prevents direct spread of action potentials from atria to ventricles(lets all 4 chambers contract separately)

Layers of the heart

1. serous pericardium 2. epicardium - visceral pericardium(outtermost layer of sac) 3. pericardial cavity - fluid filled 4. pericardial fluid - reduces friction 5. myocardium - thick cardiac muscle layer 6. endocardium - smooth(slippery) lining of heart chambers and valve coverings

Four chambers of the heart

1. two upper chambers are called atria - anterior surface of each atria has small pouch called auricle - auricles increase the capacity of the atrium 2. two lower chambers are ventricles - surface of the heart has grooves called sulci that contain blood vessels and separate the chambers

Plateau Phase in Contractile Cells

2. Plateau * depolarization also causes opening of slow calcium channels allowing calcium entry from the extracellular space and SR * at the same time, potassium efflux begins * slow calcium influx briefly balances the early potassium efflux, producing a plateau in the action potential tracing * intracellular calcium initiates cell contraction

Repolarization in Contractile Cells

3. Repolarization * the calcium channels close while more potassium channels open, allowing potassium to quickly leave the cell, resulting in repolarization * the rapid potassium efflux results in repolarization bringing the membrane potential back down to its resting potential. With the interior of the plasma membrane more negative than the exterior * ionic pumps actively transport calcium ions are pumped back out of the cell and back into the sarcoplasmic reticulum * ionic pumps also pump sodium out and potassium in * this pumping activity restores ion concentrations to their resting conditions * as the calcium is pumped out of the cell and back into the SR, the contractile cell relaxes

ECG Wave

P wave - small upward wave - indicates atrial depolarization QRS wave - downward deflection, then a large upward peak, ending as a downward deflection - represents ventricular depolarization T wave - dome-shaped wave - represents ventricular repolarization in a normal ECG tracing, atrial repolarization is hidden by the QRS complex

Intrinsic conduction system

Pathway of Depolarization 1. SA node 2. Internodal pathway 3. AV node 4. AV bundle 5. Bundle branches 6. Purkinje fibers

which represents the correct flow of excitation through the cardiac conduction system

SA node, AV node, bundle of His, right and left bundle branches, Purkinje fibers

which wave in an electrocardiogram represents repolarization of the ventricles

T wave

what is occuring during isovulumetric contraction

all four valves are closed

which of the following places the phases of the cardiac cycle in correct order

atrial contraction, isovulumetric contraction, ventricular ejection, isovolumetric relaxation, ventricular filling, atrial contraction

which of the following is false in reference to heart regulation

baroreceptors measure the amount of sodium ions present in the blood

which of the following valves are closed during isovolumetric ventricular contraction?

both the AV valve and the SL valve

which of the following valves are closed during isovolumetric ventricular relaxation?

both the AV valve and the SL valve

which network of specialized cardiac muscle fibers provides a path for each cycle of cardiac excitation to progress through the heart

cardiac conduction system

the amount of blood ejected from either ventricle every minute is called:

cardiac output

prolapse of the atrioventricular valves is prevented by

contraction of the papillary muscles

during ventricular ejection, the AV and SL valves are both closed

false

if the heart rate is 65 beats/min and the stroke volume is 70 ml, cardiac output is 135 ml/min

false

the final phase of the cardiac cycle is isovolumetric relaxation

false

the left ventricular pressure must be greater than the aortic pressure during ventricular ejection so that blood will move out through the pulmonary arteries

false

cardiac muscle fibers are electrically connected to neighboring fibers by

gap junctions

the formula for calculating cardiac output(CO) is

heart rate multiplied by stroke volume

hypertension

increases aortic pressure

contraction of the ventricles of the heart leads to blood moving directly

into arteries

the visceral layer of serous pericardium:

is the outer layer of the heart

the thickest wall in the heart due to its increased work load is the:

left ventricle

prior to physical activity, the heart rate may climb. This anticipatory increase is caused by nerve impulses traveling to the cardiovascular center of the medulla oblongata that originate in the

limbic system

Atrial Filling

meanwhile, the atria have been filling with blood. When atrial pressure exceeds ventricular pressure, AV valves open and ventricular filling, phase 1 begins again

which layer of the heart wall consists of cardiac muscle tissue

myocardium

Action Potentials in Contractile Cells

overview of action potential generation in contractile cells: 1. Depolarization - once threshold is reached, the action potential starts with depolarization 2. Plateau - during the plateau period, ion movement balances out and the membrane potential does not change very much 3. Repolarization - then repolarization begins and the membrane potential returns to its resting state

which of the following is used to reduce friction between the layers of membrane surrounding the heart

pericardial fluid

the membrane that surround and protects the heart is called the

pericardium

overview of cardiac cycle

phases of the cardiac cycle 1. ventricular filling - occurs during mid to late diastole 2. ventricular systole - includes isovolumetric contraction and ventricular ejection 3. isovolumetric relaxation - occurs during early diastole

comparatively, which phase is the longest during an action potential in a ventricular contractile fiber

refractory

which of the following chambers of the heart contains deoxygenated blood

right atrium and right ventricle

pathway of blood starting at the right atrium

right atrium, right ventricle, pulmonary trunk, pulmonary veins, left atrium, left ventricle, aorta

the purpose of the auricle is to

slightly increase the capacity of the atrium

which term refers to the period of time during a cardiac cycle when contraction of a chamber occurs and pressure within the chambers rises

systole

which of the following waves represents ventricular excitation?

the QRS wave

cardiac cycle

the cardiac cycle includes all the events related to the flow of blood through the heart during one complete heartbeat

cardiac action potential

the coordinated contractions of the hear result from electrical changes that take place in cardiac cells(coordinated and connected by gap junctions)

what occurs after the QRS phase of the ECG

the ventricles contract

which of the following is not correct

the walls of the atria are thicker because the atria receive blood under pressure

cardiac histology

three features - nuclei - intercalated discs - cardiac myofibrils

The first step of the cardiac cycle is atrial contraction

true

a skeletal muscle may undergo tetanus but cardiac muscle cannot

true

before atrial contraction, the AV valves are open and the SL valves are closed

true

cardiac output equals the stroke volume multiplied by the heart rate

true

isovolumetric contraction and isovolumetric relaxation both occur when all four valves are closed

true

parasympathetic nervous system stimulation of the heart has little effect on force of contraction because the vagus nerve does not supply most of the ventricular myocytes

true

the "lubb" sound heard during a heartbeat is actually the sound of the AV valve closing

true

the pericardium consists of a fibrous and serous layer. The visceral layer of the serous pericardium may be referred to as the epicardium

true

the plateau seen in action potentials recorded from ventricular fibers is due to inflow of Ca2+

true

the right atrium receives blood from the superior and inferior vena cava and the coronary sinus while the left atrium receives blood from the 4 pulmonary veins

true

the semilunar valves open when under pressure in the right and left ventricles exceeds that in the pulmonary trunk and aorta, respectively

true

the sympathetic impulses increase heart rate and contraction force while parasympathetic impulses decrease heart rate

true

the timing of the cardiac cycle depends on the amount of electrical activity in the heart muscle

true

stimulation of which nerve reduces heart rate

vagus nerve

Isovolumetric relaxation

ventricles relax and ventricular pressure drops, Blood backflows, closing semilunar valves. Ventricles are totally closed off again

blood pressure is highest during

ventricular ejection