1 / 33

O presente arquivo é uma coletânea de figuras e textos extraídos da coleção em CD-ROM utilizada em nossas aulas.

Atenção: Recomendamos o material a seguir apenas com o objetivo de divulgar materiais de qualidade e que estejam disponíveis gratuitamente. Profa. Cristina Maria Henrique Pinto CFS/CCB/UFSC.

kamil
Download Presentation

O presente arquivo é uma coletânea de figuras e textos extraídos da coleção em CD-ROM utilizada em nossas aulas.

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Atenção: Recomendamos o material a seguir apenas com o objetivo de divulgar materiais de qualidade e que estejam disponíveis gratuitamente. Profa. Cristina Maria Henrique Pinto CFS/CCB/UFSC O presente arquivo é uma coletânea de figuras e textos extraídos da coleção em CD-ROM utilizada em nossas aulas. “Interactive Physiology”, da Benjamin Cummings.

  2. Você pode também dar baixa destes resumos dos CD-ROM´s, não apenas de Cardiovascular mas de diversos outros assuntos de Fisiologia Humana (arquivos em *.pdf e/ou *.doc), com textos e ilustrações, diretamente do site: Selecione: “assignments”em: http://www.aw-bc.com/info/ip/ e escolha entre os seguintes assuntos: Muscular; Nervous I; Nervous II; CardiovascularRespiratory; Urinary; Fluids & ElectrolytesEndocrine e Digestive(novos) Veja também aulas online (DEMO dos CD-ROM´s) sobre: Endocrine topics eDigestive system (recém-lançados)

  3. Cardiovascular Physiology parte 2: Intrinsic Conduction System, Measuring Blood Pressure and Cardiac Action Potenctial Profa. Cristina Maria Henrique Pinto - CFS/CCB/UFSC monitores: Vinicius Negri Dall'Inha e Grace Keli Bonafim (graduandos de Medicina) Este arquivo está disponível em: http://www.cristina.prof.ufsc.br/md_cardiovascular.htm

  4. 2ª parte: Intrinsic Conduction System, Measuring Blood Pressure and Cardiac Action Potenctial Intrinsic Conduction System Graphics are used with permission of: Pearson Education Inc., publishing as Benjamin Cummings (http://www.aw-bc.com) 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) throughout the heart. Goals • To identify the components of the intrinsic conduction system. • To recognize that the intrinsic conduction system coordinates heart activity by determining the direction and speed of heart depolarization. • To relate heart electrical activity to an ECG wave tracing Intrinsic Conduction System • This diagram shows the location of the autorhythmic, or nodal cells of the intrinsic conduction system: SA Node Internodal Pathway AV Node AV Bundle Bundle Branches Purkinje Fibers

  5. • Label this diagram:

  6. Pathway of Depolarization SA Node • Located in upper right atrium. • Initiates the depolarization impulse which, in turn, generates an action potential that spreads throughout the atria to the AV node. • Sets the overall pace of the heartbeat. 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. 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. 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. Bundle Branches • Convey the action potential down the interventricular septum. 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 potential 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.

  7. ECG Wave ECG Waves: 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. • On the following diagram indicate where the following normally occur: atrial depolarization, ventricular depolarization, ventricular repolarization, atrial repolarization

  8. 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 complex Represents ventricular depolarization which is followed by ventricular contraction. T wave Represents ventricular repolarization which is followed by ventricular relaxation. 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. Notes on Quiz Questions: Quiz Question 1. Conduction Pathway • This question asks you to match the various autorhythmic cells of heart to their functions. Quiz Question 2. ECG Puzzle • This question asks you to piece together a normal ECG Tracing. Quiz Question 3a & 3b. Create Left Bundle Branch Block • This question asks you to create a left bundle branch block and predict what would happen to the ECG tracing. • If you have a difficult time understanding the correct answer, please note that normally the left ventricle is depolarized when impulses move along the left bundle branch and to the Purkinje fibers. If the left bundle branch is blocked, ventricular depolarization takes longer because impulses in the left ventricle must travel from cell to cell. Because ventricular depolarization is taking longer, the QRS complex is wider. Quiz Question 4. ECG for Tachycardia • This question allows you to chose the ECG Wave tracing that corresponds to Tachycardia • With a normal heart rate of 75 beats per minute, one heartbeat takes 0.8 seconds. (1 minute/75 beats) (60 seconds/1 minute) = 0.8 seconds • An abnormally fast heart rate, such as 120 beats per minutes, one heartbeat takes 0.5 seconds. (1 minute/120 beats) (60 seconds/1 minute) = 0.5 seconds

  9. Study Questions on the Intrinsic Conduction System: 1. What is the purpose of the intrinsic conduction system of the heart? 2. What type of cells are present in the intrinsic conduction system of the heart? 3. List the six areas within the heart where autorhythmic cells are found. 4. Match the six areas within the heart where autorhythmic cells are found to their location within the heart. Location Within the Heart: a. Interatrial septum to the interventricular septum. b. Lower interventricular septum to the myocardium of the ventricles. c. Inferior interatrial septum. d. Upper right atrium. e. Throughout the walls of the atria. f. Within the interventricular septum Areas Where Autorhythmic Cells Are Found: Internodal Pathway AV Node Bundle Branches SA Node Purkinje Fibers AV Bundle 5. (Page 4.) Match the six areas within the heart where autorhythmic cells are found to their function. Functions: a. Initiates the depolarization impulse that generates an action potential, setting the overall pace of the heartbeat. b. Convey the action potential to the contractile cells of the ventricle. c. Delays the action potential while the atria contract. d. Links the SA node to the AV node, distributing the action potential to the contractile cells of the atria. e. Electrically connects the atria and the ventricles, connecting the AV node to the Bundle Branches. f. Conveys the action potential down the interventricular septum. Areas Where Autorhythmic Cells Are Found: Internodal Pathway AV Node Bundle Branches SA Node Purkinje Fibers AV Bundle

  10. 6. Explain the difference between the electrical and mechanical events which occur within the heart, and explain the cell types that carry out each. Which occurs first, the electrical or mechanical events? 7. In an ECG tracing, how are the following represented: a. atrial depolarization. b. atrial repolarization c. ventricular depolarization d. ventricular repolarization. 8. Why is it important for the contraction of the ventricle to begin at the apex and move superiorly. 9 a. The P wave indicates the electrical event of atrial depolarization. What mechanical event follows the P wave? b. The QRS complex indicates the electrical event of ventricular depolarization. What mechanical event follows the QRS complex? c. The T wave indicates the electrical event of ventricular repolarization. What mechanical event follows the T wave ?

  11. 10. Match the appearance of the heart to its position on the ECG tracing.

  12. Measuring Blood Pressure Graphics are used with permission of: Pearson Education Inc., publishing as Benjamin Cummings (http://www.aw-bc.com) Introduction • Blood pressure is an important indicator of cardiovascular health. It is influenced by the contractile activities of the heart and conditions and activities of the blood vessels. Goals • To understand the terminology associated with measuring blood pressure. • To understand the sounds heard during blood pressure measurement. Blood Pressure Defined • Blood Pressure is the force that blood exerts against blood vessel walls. • The pumping action of the heart generates blood flow. • Blood pressure results when that flow is met by resistance from vessel walls. • Blood pressure is expressed in millimeters of mercury (mm Hg). For example a blood pressure of 120 mm Hg is equivalent to a pressure exerted by a column of mercury 120 mm high. Laminar Flow • Blood flows faster in the center of a vessel than near the sides, because the blood near the sides are hitting the walls of the vessels. This is called laminar flow and it is due to the friction (resistance) between the blood and the vessel walls. Blood Pressure Graph • By taking your pulse, you can feel that blood pressure fluctuates with each heartbeat. The pulse which you feel is actually a pressure wave which travels from your heart throughout the arteries. • We can use the graph created by this pressure wave to identify the component parts of blood pressure. • Label the parts of this graph as you go through the next few pages:

  13. Systolic Pressure • Systolic pressure is the maximum pressure exerted by the blood against the artery walls. It is the result of ventricular systole or contraction. It is normally about 120 mm Hg. . Dicrotic Notch • The dicrotic notch represents the interruption of smooth flow due to the brief backflow of blood that closes the aortic semilunar valve when the ventricles relax. Diastolic Pressure • Diastolic pressure is the lowest pressure in the artery. It's a result of ventricular diastole (relaxation) and is usually around 80 mm Hg.

  14. Pulse Pressure • Pulse Pressure is the difference between systolic and diastolic pressure. • It's the throb you feel when you take your pulse. Pulse Pressure = Systolic Pressure - Diastolic Pressure ~ 40 mm Hg ~120 mm Hg - ~80 mm Hg . Mean Arterial Pressure (MAP) • Mean Arterial Pressure (MAP) is a calculated "average" pressure in the arteries. Mean Arterial Pressure (MAP) = Diastolic Pressure + 1/3 Pulse Pressure ~93 mm Hg = ~80 mm Hg + ~ 40 mm Hg 3 • MAP is closer to the diastolic pressure than systolic pressure because the heart stays longer in diastole. • MAP is the force that propels the blood through the arteries. Blood Pressure Sounds • When blood pressure is measured, a cuff is inflated to constrict an artery so that no blood flows through. Since the pressure in the cuff is greater than the pressure in the artery, the artery is closed off and no blood flows through. • As the cuff pressure is gradually released, but the artery is still partially constricted, blood flow resumes. Sounds can be heard with a stethoscope because the blood flows turbulently, causing audible sounds. • When enough pressure is released to fully open the artery, the blood flows freely and the sounds disappear because smooth flowing blood does not create sounds.

  15. Checking Blood Pressure • The first sounds that are heard indicate systolic pressure. When the sounds stop, diastolic pressure has been reached. Summary • Systolic pressure = highest pressure in an artery; result of ventricular contraction • Diastolic pressure = lowest pressure in an artery; result of ventricular relaxation • Pulse pressure = systolic pressure - Diastolic Pressure • Mean Arterial Pressure (MAP) = Diastolic pressure + 1/3 Pulse pressure • When blood pressure is measured, first sounds indicate systolic pressure; end of sounds indicates diastolic pressure. Notes on Quiz Questions: Quiz Question 1. Blood Pressure Measurement • This question asks you to determine a blood pressure. Quiz Question 2. Pulse Pressure Calculation • This question asks you to determine a pulse pressure. Quiz Question 3. MAP Calculation • This question asks you to calculate a mean arterial pressure. Study Questions on Measuring Blood Pressure: 1. What is the term used to express the force that blood exerts against the walls of blood vessels? 2. How is blood pressure generated? 3. In what units is blood pressure expressed? 4. Does blood flow at the same rate in the exact center of a vessel compared to at the sides of the vessel? 5. What is laminar flow and what causes it?

  16. 6. What is a pulse? 7. What is systolic pressure and what causes it? 8. What is ventricular systole? 9. What is a typical normal value for systolic pressure? 10. What does the dicrotic notch represent? 11. What is diastolic pressure and what causes it? 12. What is ventricular diastole? 13. What is a typical normal value for diastolic pressure? 14. What is pulse pressure? 15. (Page 9.) If the systolic pressure is 120 mm Hg and the diastolic pressure is 80 mm Hg, what would the pulse pressure be? 16. Match these terms to their characteristic: a. the throb you feel when you take your pulse b. interruption of smooth flow due to the brief backflow of blood c. result of ventricular diastole d. the force that propels the blood through the arteries e. the result of ventricular systole 1. Systolic Pressure 2. Dicrotic Notch 3. Diastolic Pressure 4. Pulse Pressure 5. Mean Arterial Pressure

  17. 17. Why is mean arterial pressure closer to diastolic pressure than systolic pressure? 18. Calculate the mean arterial pressure when systolic pressure is 120 mm Hg and the diastolic pressure is 80 mm Hg. 19.What do the sounds correspond to when a blood pressure is taken?

  18. Você pode ver a aula a seguir, diretamente do site, online. Clique abaixo

  19. Cardiac Action Potential Graphics are used with permission of: Pearson Education Inc., publishing as Benjamin Cummings (http://www.aw-bc.com) Introduction • The coordinated contractions of the heart result from electrical changes that take place in cardiac cells. Goals • To understand the ionic basis of the pacemaker potential and the action potential in a cardiac autorhythmic muscle cell. • To understand the ionic basis of an action potential in a cardiac contractile (ventricular) cell. • To understand that autorhythmic and contractile cells are electrically coupled by current that flows through gap junctions. 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.

  20. Gap Junctions • Action potentials generated by autorhythmic cells create waves of depolarization that spread to contractile cells via gap junctions. • Label the parts of this diagram: 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.

  21. 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. • Label the components of this autorhythmic cell:

  22. 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 spontaneously begins to slowly depolarize again and the sequence is repeated. 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. 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.

  23. Repolarization in Autorhythmic Cells • This reversal of membrane potential triggers 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. 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. • Label the parts of the cardiac contractile cell on the top of the next page.

  24. 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. 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 (Ca+2 and Na+1 ) 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.

  25. 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 level. 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.

  26. Action Potential Waves and Graphs Summary • 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 sodium 2. Plateau produced by calcium influx balancing potassium efflux. 3. Repolarization due to efflux of potassium.

  27. Notes on Quiz Questions: Quiz Question 1. Membrane Potential • This question asks you to drag the proper charge to the inside and outside of the cardiac contractile cells during both the repolarized and depolarized states. Quiz Question 2a. Pacemaker Potential in Autorhythmic Cell • This question asks you to identify the channel that brings about the pacemaker potential in a cardiac autorhythmic cell. Quiz Question 2b. Depolarization in Autorhythmic Cell • This question asks you to identify the channel that brings about depolarization and reversal of membrane potential in a cardiac autorhythmic cell. Quiz Question 2c. Repolarization in Autorhythmic Cell • This question asks you to identify the channel that brings about repolarization in a cardiac autorhythmic cell. Quiz Question 3. Gap Junction • This question allows you to identify the channel that allows positive ions to move from one cardiac cell to another. Quiz Question 4a. Depolarization in Contractile Cell • This question asks you to identify the channel that brings about depolarization in contractile cells. Quiz Question 4b. Plateau in Contractile Cell • This question asks you to identify the channels that brings about plateau in contractile cells. Quiz Question 4c. Repolarization in Contractile Cell • This question asks you to identify the channel that brings about repolarization in contractile cells.

  28. Study Questions on the Cardiac Action Potential: 1. What two cell types are involved in producing a coordinated heart contraction? 2. How do the cardiac autorhythmic cells and cardiac contractile cells work together to produce a coordinated heart contraction? 3. Before cardiac autorhythmic and contractile cells depolarize, what is the charge inside and outside the cell. 4. When cardiac autorhythmic and contractile cells depolarize, what happens to the charge inside and outside the cell. 5. When cardiac autorhythmic and contractile cells repolarize, what happens to the charge inside and outside the cell. 6. When do cardiac contractile cells contract and relax with respect to depolarization and repolarization of the cell. 7. Embedded in the plasma membrane of an autorhythmic cell are protein channels that allow sodium, calcium, and potassium to move into or out of the cell. In which direction do the ions move through these channels? 8. What is the function of gap junctions? 9. What are the three steps in the initiation of action potential in an autorhythmic cell? 10. What is responsible for the pacemaker potential? 11. What is the order of steps in an action potential within an autorhythmic cell. a. Fast calcium channels open and positively-charged calcium ions rush in. b. Depolarization peaks at about +10 mV. c. Autorhythmic cell starts out at resting membrane potential (~-60 mV), positive out, negative in. d. When the membrane potential gets to -40 millivolts, it has reached threshold for initiating an action potential. e. Potassium channels open, resulting in potassium rapidly leaving the cell. f. Cell begins depolarizing due to a slow continuous influx of sodium. g. 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. h. Membrane potential goes from +10 mV to resting membrane potential (-60 mV). 12. What is responsible for reestablishing ion levels in autorhythmic cells?

  29. A. Repolarization B. Pacemaker Potential C. Depolarization and reversal of the membrane potential x. due to influx of sodium y. due to efflux of potassium z. due to influx of calcium 13. Match the following events in autorhythmic cells: 14. Label the parts of this action potential tracing in autorhythmic cells: A. Repolarization B. Pacemaker Potential C. Depolarization and reversal of the membrane potential

  30. 15. What allows depolarization to move from autorhythmic cells to the contractile cells? 16. What allows depolarization to move from one contractile cell to another contractile cells? 17. Where is calcium stored within contractile cells? 18. What are the three steps in the action potential in a contractile cell? 19. What is the order of steps in an action potential within an contractile cell. a. Intracellular calcium initiates cell contraction. b. Neighboring cells (either autorhythmic or contractile cells) depolarize. c. Rapid influx of sodium results in depolarization, resulting in a reversal of charge (depolarization) (to about +25 mV) as sodium moves into the cell. d. Ionic pumps actively transport calcium ions out of the cell and back into the sarcoplasmic reticulum. Ionic pumps also pump sodium out and potassium in, restoring ion concentrations to their resting conditions. e. The calcium channels close while more potassium channels open, allowing potassium to quickly leave the cell, resulting in repolarization. f. Gap junctions open and positive ions (Ca+2 and Na+1 ) move in to the contractile cells through gap junctions. g. Depolarization also causes opening of slow calcium channels, allowing calcium entry from the extracellular space and SR. At the same time, potassium efflux begins producing a plateau in the action potential tracing. h. At rest, contractile cells have a resting membrane potential of about -90 mV. i. As the calcium is pumped out of the cell and back into the SR, the contractile cell relaxes. j. A small voltage change (of about 5 mV to about -85 mV) occurs, which initiates depolarization 20. Are neurotransmitters involved in the transmission of depolarization from one cardiac muscle cell to another?

  31. A. Repolarization B. Depolarization C. Plateau 21. Label the parts of this action potential tracing in contractile cells: 22. Match the position of the end of these action potential tracings to the corresponding appearance of the cells: (See next page.)

  32. Cardiovascular Physiology continua em: parte 3: Factors thatAffect Blood Pressure, Cardiac Cycle, Cardiac Output parte 4: Blood Pressure Regulation and Autoregulation and Capillary Dynamics parte 1: Anatomy review: the heart, anatomy review: blood vessel and structure and function Profa. Cristina Maria Henrique Pinto - CFS/CCB/UFSC monitores: Vinicius Negri Dall'Inha e Grace Keli Bonafim (graduandos de Medicina) Este arquivo está disponível em: http://www.cristina.prof.ufsc.br/md_cardiovascular.htm

More Related