© 2018 Pearson Education, Inc.

Introduction The heart keeps the blood in motion
If blood stops moving, nutrient and oxygen supplies are exhausted and wastes accumulate The heart beats about 100,000 times per day This is about 70 beats per minute The heart pumps about 1.5 million gallons of blood per year This is about 2.9 gallons per minute The heart pumps between 5 and 30 liters of blood per minute—It can vary widely © 2018 Pearson Education, Inc.

An Overview of the Cardiovascular System
The heart is about the size of a clenched fist The heart consists of four chambers Two atria Two ventricles The heart pumps blood into two circuits Pulmonary circuit Systemic circuit © 2018 Pearson Education, Inc.

Figure 21.5 Superficial Anatomy of the Heart, Part I
Left atrium Right atrium Right atrium Left ventricle Right ventricle Left ventricle Right ventricle a Anterior view of the heart and great vessels b Posterior view of the heart and great vessels © 2018 Pearson Education, Inc.

Figure 21.1 A Generalized View of the Pulmonary and Systemic Circuits
Pulmonary Circuit Systemic Circuit Pulmonary arteries Systemic arteries Pulmonary veins Systemic veins Capillaries in head and neck Pulmonary arteries Systemic arteries Capillaries in lungs Left atrium Pulmonary veins Left ventricle Capillaries in abdominal organs Right atrium Right ventricle Systemic veins Capillaries in upper limbs Capillaries in trunk and lower limbs © 2018 Pearson Education, Inc.

An Overview of the Cardiovascular System
Each circuit involves arteries, veins, and capillaries Arteries Transport blood away from the heart Veins Transport blood toward the heart Capillaries Vessels that interconnect arteries and veins © 2018 Pearson Education, Inc.

The Pericardium The heart is surrounded by a pericardium, consisting of two parts: An outer fibrous pericardium An inner serous pericardium, which consists of two layers An inner visceral layer, also called epicardium, is attached to the surface of the heart An outer parietal layer, which is adjacent to the fibrous pericardium The space between the two serous layers is called the pericardial cavity and it contains pericardial fluid Pericardial fluid lubricates the space to reduce friction © 2018 Pearson Education, Inc.

Figure 21.2a Location of the Heart in the Thoracic Cavity
Trachea Thyroid gland Right lung First rib (cut) Left lung Base of heart Parietal pericardium (cut) Apex of heart Diaphragm a Anterior view of the open chest cavity showing the position of the heart, major vessels, and lungs. The sectional plane indicates the orientation of part (c). © 2018 Pearson Education, Inc.

Figure 21.2b Location of the Heart in the Thoracic Cavity
Air space (corresponds to pericardial cavity) Cut edge of parietal layer Pericardial cavity containing pericardial fluid Cut edge of epicardium (visceral layer) Fibrous attachment to diaphragm Balloon b Relationships between the heart and the pericardial cavity. The pericardial cavity surrounds the heart like the balloon surrounds the fist (right). © 2018 Pearson Education, Inc.

Structure of the Heart Wall
The walls of the heart consist of three layers: Epicardium External surface, consists of visceral pericardium Myocardium Consists of cardiac tissue, including cardiac muscle cells, connective tissue, blood vessels, and nerves Endocardium Internal, endothelial surface © 2018 Pearson Education, Inc.

Anterior view of the heart showing several important landmarks.
Figure 21.3ab Histological Organization of Muscle Tissue in the Heart Wall Base of heart Pericardial cavity Pericardial cavity Myocardium (cardiac muscle tissue) Parietal layer of serous pericardium Dense fibrous layer Cut edge of pericardium Areolar tissue Mesothelium Artery Vein Apex of heart Endocardium Endothelium Connective tissues a Anterior view of the heart showing several important landmarks. Areolar tissue Visceral layer of serous pericardium (epicardium) Mesothelium Areolar tissue b A section through the heart wall showing the structure of the epicardium, myocardium, and endocardium. © 2018 Pearson Education, Inc.

Cardiac Muscle Tissue Striated appearance Dependent on aerobic respiration Lots of mitochondria and myoglobin The circulatory supply of cardiac muscle tissue is very extensive Cardiac muscle cells contract without information coming from the CNS (involuntary) Cardiac muscle cells are interconnected by intercalated discs © 2018 Pearson Education, Inc.

Intercalated disc Nucleus c
Figure 21.3c Histological Organization of Muscle Tissue in the Heart Wall Intercalated disc Nucleus Cardiac muscle tissue LM × 575 c Histological view of cardiac muscle tissue. Distinguishing characteristics of cardiac muscle cells include (1) small size; (2) a single, centrally placed nucleus; (3) branching interconnections between cells; and (4) the presence of intercalated discs. © 2018 Pearson Education, Inc.

Three-dimensional view of cardiac muscle cells.
Figure 21.3d Histological Organization of Muscle Tissue in the Heart Wall Cardiac muscle cell Mitochondria Intercalated disc (sectioned) Nucleus Cardiac muscle cell (sectioned) Bundles of myofibrils Intercalated disc d Three-dimensional view of cardiac muscle cells. © 2018 Pearson Education, Inc.

Cardiac Muscle Tissue The Intercalated Discs Cardiac cells have specialized cell-to-cell junctions The plasma membranes of two adjacent cardiac cells are bound together by desmosomes The intercalated discs bind the myofibrils of adjacent cells together Cardiac muscle cells are connected by gap junctions Ions move directly from one cell to another creating a direct, electrical connection allows all the muscle cells to form a functional syncytium (contract as one unit) © 2018 Pearson Education, Inc.

Three-dimensional view of cardiac muscle cells.
Figure 21.3de Histological Organization of Muscle Tissue in the Heart Wall Cardiac muscle cell Mitochondria Intercalated disc (sectioned) Nucleus Cardiac muscle cell (sectioned) Intercalated disc Bundles of myofibrils Gap junction Intercalated disc Z lines bound to opposing plasma membranes d Three-dimensional view of cardiac muscle cells. Desmosomes e The structure of an intercalated disc. © 2018 Pearson Education, Inc.

The Cardiac Skeleton Each cardiac cell is wrapped in an elastic sheath Each muscle layer is wrapped in a fibrous sheet The fibrous sheets separate the superficial layer from the deep layer muscles These fibrous sheets also encircle the base of the pulmonary trunk, ascending aorta, and valves © 2018 Pearson Education, Inc.

Functions of the cardiac skeleton Stabilizes the position of cardiac cells Stabilizes the position of the heart valves Provides support for the blood vessels and nerves in the myocardium Helps to distribute the forces of contraction Helps to prevent overexpansion of the heart Provides elasticity so the heart recoils after contraction Isolates atrial cells from ventricular cells © 2018 Pearson Education, Inc.

Orientation and Superficial Anatomy of the Heart
The heart lies slightly to the left of midsagittal plane Located in the mediastinum The base is the superior border of the heart The apex is the inferior portion of the heart The right border is formed by only the right atrium The inferior border is formed by the right ventricle © 2018 Pearson Education, Inc.

The heart is rotated slightly toward the left The anterior surface consists of the right atrium, right ventricle, and the left ventricle The posterior surface consists of the left atrium and a small portion of right atrium The diaphragmatic surface is composed of the right and left ventricles © 2018 Pearson Education, Inc.

Figure 21.4 Position and Orientation of the Heart
Superior border Base of heart 1 1 Ribs 2 2 3 3 4 4 Right border Left border 5 5 6 6 7 7 Apex of heart 8 8 9 9 10 10 Inferior border © 2018 Pearson Education, Inc.

The four chambers of the heart can be identified by sulci (grooves) on the external surface Interatrial groove separates the left and right atria Coronary sulcus separates the atria and the ventricles Anterior interventricular sulcus separates the left and right ventricles Posterior interventricular sulcus also separates the left and right ventricles © 2018 Pearson Education, Inc.

Left common carotid artery Left subclavian artery Arch of aorta Arch of aorta Brachiocephalic trunk Ligamentum arteriosum Left pulmonary artery Right pulmonary artery Left pulmonary veins (superior and inferior) Descending aorta Superior vena cava Ascending aorta Left pulmonary artery Superior vena cava Left atrium Pulmonary trunk Fat in coronary sulcus Right pulmonary veins (superior and inferior) Auricle of right atrium Auricle of left atrium Coronary sinus Right atrium Right atrium Left ventricle Fat in anterior interventricular sulcus Inferior vena cava Right ventricle Fat in coronary sulcus Left ventricle Right ventricle Fat in posterior interventricular sulcus a Anterior view of the heart and great vessels b Posterior view of the heart and great vessels © 2018 Pearson Education, Inc.

The left and right atria Positioned superior to the coronary sulcus Both have thin walls Both contain an expandable anterior portion called an auricle The left and right ventricles Positioned inferior to the coronary sulcus Both have thicker walls than the atria Left ventricular wall is thicker than the right ventricular wall © 2018 Pearson Education, Inc.

Left common carotid artery Left subclavian artery Arch of aorta Arch of aorta Brachiocephalic trunk Ligamentum arteriosum Left pulmonary artery Right pulmonary artery Left pulmonary veins (superior and inferior) Descending aorta Superior vena cava Ascending aorta Left pulmonary artery Superior vena cava Left atrium Pulmonary trunk Fat in coronary sulcus Right pulmonary veins (superior and inferior) Auricle of right atrium Auricle of left atrium Coronary sinus Right atrium Right atrium Left ventricle Fat in anterior interventricular sulcus Inferior vena cava Right ventricle Fat in coronary sulcus Left ventricle Right ventricle Fat in posterior interventricular sulcus a Anterior view of the heart and great vessels b Posterior view of the heart and great vessels © 2018 Pearson Education, Inc.

Internal Anatomy and Organization of the Heart
A frontal section of the heart reveals: Left and right atria separated by the interatrial septum Left and right ventricles separated by the interventricular septum The atrioventricular valves are formed from folds of endocardium The atrioventricular valves are situated between the atria and the ventricles © 2018 Pearson Education, Inc.

Figure 21.7b Sectional Anatomy of the Heart, Part I
Interatrial septum Interventricular septum b Frontal section of the relaxed heart showing the major landmarks and the path of blood flow (arrows) through the atria and ventricles. © 2018 Pearson Education, Inc.

The Right Atrium Receives oxygen-poor venous blood via the superior vena cava, inferior vena cava, and coronary sinus Coronary sinus enters the posterior side of the right atrium Contains pectinate muscles Anterior wall and auricle Interatrial septum contains the fossa ovalis fetal remnant of the foramen ovale that allowed fetal blood to bypass the lungs © 2018 Pearson Education, Inc.

Superior vena cava Fossa ovalis Opening of coronary sinus Right atrium Pectinate muscles Inferior vena cava b Frontal section of the relaxed heart showing the major landmarks and the path of blood flow (arrows) through the atria and ventricles. © 2018 Pearson Education, Inc.

The Right Ventricle Receives oxygen-poor blood from the right atrium Blood enters the right ventricle by passing through the right atrioventricular valve Also called right AV valve or tricuspid valve Blood leaves the right ventricle by passing through the pulmonary valve Also called pulmonary semilunar valve Leads to the pulmonary trunk, then to the right and left pulmonary arteries © 2018 Pearson Education, Inc.

The Right Ventricle The right AV valve is connected to papillary muscles via chordae tendineae There are three fibrous flaps or cusps and three papillary muscles Each of the three cusps is connected by the chordae tendineae to separate papillary muscles Papillary muscles and chordae tendineae prevent valve inversion when the ventricles contract © 2018 Pearson Education, Inc.

Figure 21.7 Sectional Anatomy of the Heart, Part I
Pulmonary trunk Pulmonary valve Right pulmonary arteries Left pulmonary arteries Cusp of right AV (tricuspid) valve Chordae tendineae Papillary muscle Right ventricle a Photograph of papillary muscles and chordae tendineae supporting the right AV valve. The picture was taken inside the right ventricle, looking toward a light shining from the right atrium. b Frontal section of the relaxed heart showing the major landmarks and the path of blood flow (arrows) through the atria and ventricles. © 2018 Pearson Education, Inc.

The Right Ventricle The internal surface of the right ventricle consists of: Trabeculae carneae Muscular ridges Moderator band Found only in the right ventricle Muscular band that extends from the interventricular septum to the ventricular wall Prevents overexpansion of the thin-walled right ventricle © 2018 Pearson Education, Inc.

Trabeculae carneae Right ventricle Moderator band b Frontal section of the relaxed heart showing the major landmarks and the path of blood flow (arrows) through the atria and ventricles. © 2018 Pearson Education, Inc.

The Left Atrium Receives oxygenated blood from the lungs via the right and left pulmonary veins Pectinate muscles restricted to auricle Blood passes through the left atrioventricular valve bicuspid valve or left AV valve Also called the mitral valve © 2018 Pearson Education, Inc.

Left pulmonary veins Left atrium Pectinate muscles Cusp of left AV (mitral) valve b Frontal section of the relaxed heart showing the major landmarks and the path of blood flow (arrows) through the atria and ventricles. © 2018 Pearson Education, Inc.

The Left Ventricle Has the thickest wall Needed for strong contractions to pump blood throughout the entire systemic circuit Compare to the right ventricle, which has a thin wall since it only pumps blood through the pulmonary circuit Does not have a moderator band Prominent trabeculae carneae The left AV valve has chordae tendineae connecting to two cusps and to two papillary muscles © 2018 Pearson Education, Inc.

The Left Ventricle Blood leaves the left ventricle by passing through the aortic valve Also called aortic semilunar valve Blood enters the ascending aorta Blood then travels to the aortic arch and then down the descending aorta and to all body parts (systemic) © 2018 Pearson Education, Inc.

Aortic arch Ascending aorta Aortic valve Left ventricle Trabeculae carneae Descending aorta b Frontal section of the relaxed heart showing the major landmarks and the path of blood flow (arrows) through the atria and ventricles. © 2018 Pearson Education, Inc.

Structural Differences between the Right and Left Ventricles Right ventricle Thinner wall Weaker contraction Has a moderator band Left ventricle Thicker wall Powerful contraction Six to seven times more powerful than the right ventricle © 2018 Pearson Education, Inc.

Figure 21.8 Sectional Anatomy of the Heart, Part II
Left subclavian artery Left common carotid artery Brachiocephalic trunk Left AV (mitral) valve Superior vena cava Pulmonary trunk Superior vena cava Ascending aorta Chordae tendineae Cusp of pulmonary valve Left atrium Auricle of left atrium Right atrium Cusp of left AV (mitral) valve Chordae tendineae Papillary muscles Cusps of right AV (tricuspid) valve Left ventricle Papillary muscles of left ventricle Trabeculae carneae Interventricular septum Pectinate muscles Trabeculae carneae of right ventricle Interventricular septum Right ventricle a Anterior view of a frontally sectioned heart showing internal features and valves b Inferior view of a horizontal section through the heart at the level of vertebra T8 © 2018 Pearson Education, Inc.

The Structure and Function of Heart Valves There are four valves in the heart Two AV valves Tricuspid and bicuspid valves Two semilunar valves Aortic and pulmonary valves © 2018 Pearson Education, Inc.

The Structure and Function of Heart Valves Each AV valve consists of four parts Ring of connective tissue Connects to the heart tissue Part of fibrous skeleton of the heart Cusps Chordae tendineae Connect to the cusps and papillary muscles Papillary muscles Contract in such a manner to prevent AV valve inversion © 2018 Pearson Education, Inc.

Figure 21.9a Valves of the Heart
Transverse Sections, Superior View, Atria and Vessels Removed Frontal Sections through Left Atrium and Ventricle POSTERIOR Cardiac skeleton Left AV (mitral) valve (open) Pulmonary veins Right ventricle Left ventricle Left atrium Relaxed ventricles Left AV (mitral) valve (open) Chordae tendineae (loose) Aortic valve (closed) Right AV (tricuspid) valve (open) Papillary muscles (relaxed) Left ventricle (dilated) Aortic valve (closed) Pulmonary valve (closed) ANTERIOR a When the ventricles are relaxed, the AV valves are open and the semilunar valves are closed. The chordae tendineae are loose, and the papillary muscles are relaxed. Aortic valve closed © 2018 Pearson Education, Inc.

The Structure and Function of Heart Valves AV valve function during the cardiac cycle Papillary muscles relax Due to pressure in the atria, the AV valves open Blood flows from atria to ventricle When the ventricles contract, pressure causes the AV valves to close and semilunar valves to open Closure of AV valves prevents regurgitation or backflow into the atria This forces blood through the open semilunar valves © 2018 Pearson Education, Inc.

Figure 21.9a Valves of the Heart
Transverse Sections, Superior View, Atria and Vessels Removed Frontal Sections through Left Atrium and Ventricle POSTERIOR Cardiac skeleton Left AV (mitral) valve (open) Pulmonary veins Right ventricle Left ventricle Left atrium Relaxed ventricles Left AV (mitral) valve (open) Chordae tendineae (loose) Aortic valve (closed) Right AV (tricuspid) valve (open) Papillary muscles (relaxed) Left ventricle (dilated) Aortic valve (closed) Pulmonary valve (closed) ANTERIOR a When the ventricles are relaxed, the AV valves are open and the semilunar valves are closed. The chordae tendineae are loose, and the papillary muscles are relaxed. Aortic valve closed © 2018 Pearson Education, Inc.

Figure 21.9b Valves of the Heart
Right AV (tricuspid) valve (closed) Cardiac skeleton Left AV (mitral) valve (closed) Right ventricle Left ventricle Aorta Left atrium Aortic sinus Contracted ventricles Left AV (mitral) valve (closed) Aortic valve (open) Chordae tendineae (tense) Papillary muscles (contracted) Aortic valve (open) Left ventricle (contracted) Pulmonary valve (open) b When the ventricles are contracting, the AV valves are closed and the semilunar valves are open. In the frontal section notice the attachment of the left AV valve to the chordae tendineae and papillary muscles. Aortic valve open © 2018 Pearson Education, Inc.

Coronary Blood Vessels
Originate at the base of the ascending aorta Supply the cardiac muscle tissue via the coronary circulation The major coronary arteries Right coronary artery (RCA) Atrial branches Right marginal branch Posterior interventricular branch Left coronary artery (LCA) Circumflex branch Left marginal branch Anterior interventricular branch © 2018 Pearson Education, Inc.

The Right Coronary Artery Passes between the right auricle and pulmonary trunk Major branches off the right coronary artery: Atrial branches Right marginal branch Posterior interventricular branch Conducting system branches © 2018 Pearson Education, Inc.

Figure 21.10a Coronary Circulation
Pulmonary trunk Right coronary artery (RCA) Atrial branches of RCA Marginal branch of RCA a Coronary vessels supplying the anterior surface of the heart. © 2018 Pearson Education, Inc.

The Left Coronary Artery Major branches off the left coronary artery Anterior interventricular branch Branches that lead to the posterior interventricular branch called anastomoses Circumflex branch Branches to form the left marginal branch Branches to form the posterior left ventricular branch © 2018 Pearson Education, Inc.

Figure 21.10b Coronary Circulation
Marginal branch of LCA Posterior left ventricular branch of LCA b Coronary vessels supplying the posterior surface of the heart. © 2018 Pearson Education, Inc.

The Coronary Veins Drain cardiac venous blood ultimately into the right atrium Main coronary veins Great cardiac vein Delivers blood to the coronary sinus Middle cardiac vein Coronary sinus Drains directly into the posterior aspect of the right atrium © 2018 Pearson Education, Inc.

The Coronary Veins Main coronary veins Posterior vein of the left ventricle Parallels the posterior left ventricular branch Small cardiac vein Parallels the right coronary artery Anterior cardiac veins Branches from the right ventricle cardiac cells © 2018 Pearson Education, Inc.

Figure 21.10b Coronary Circulation
Great cardiac vein Posterior vein of left ventricle Coronary sinus Small cardiac vein Middle cardiac vein b Coronary vessels supplying the posterior surface of the heart. © 2018 Pearson Education, Inc.

The Coordination of Cardiac Contractions
The cardiac cycle consists of alternate periods of contraction and relaxation Contraction is systole Atrial systole Blood flows into the ventricles Ventricular systole Blood is ejected into the pulmonary trunk and the ascending aorta Relaxation is diastole Chambers are filling with blood © 2018 Pearson Education, Inc.

Figure 21.11 The Conducting System and the Cardiac Cycle (3 of 6)
Atrial systole begins: Atrial contraction forces a small amount of blood into the relaxed ventricles. Start Atrial systole ends; atrial diastole begins: Atrial diastole continues until the start of the next cardiac cycle. 800 msec msec 100 msec Cardiac cycle Ventricular systole— first phase: Ventricular contraction pushes the AV valves closed but does not create enough pressure to open the semilunar valves. Ventricular diastole—late: All chambers are relaxed. The AV valves open and the ventricles fill passively. 370 msec Ventricular systole— second phase: As ventricular pressure rises and exceeds the pressure in the arteries, the semilunar valves open and blood is ejected. Ventricular diastole—early: As the ventricles relax, the ventricular blood pressure drops until reverse blood flow pushes the cusps of the semilunar valves together. Blood now flows into the relaxed atria. © 2018 Pearson Education, Inc.

The Coordination of Cardiac Contractions
Cardiac contractions of the cardiac cycle are coordinated by conducting cells There are two kinds of conducting cells Nodal cells Sinoatrial nodes and atrioventricular nodes Establish the rate of contractions Cell membranes automatically depolarize (autorhythmic) Conducting cells Distribute the contractile stimulus to the myocardium © 2018 Pearson Education, Inc.

The Cardiac Cycle Sinoatrial node (SA node)
Located in the posterior wall of the right atrium near the entrance of the superior vena cava Also called the cardiac pacemaker Pacemaker cells in the SA node automatically generate 80–100 action potentials per minute Bradycardia—slower-than-normal heart rate Tachycardia—faster-than-normal heart rate Atrioventricular node (AV node) Sits within the floor of the right atrium © 2018 Pearson Education, Inc.

The Cardiac Cycle Summary of cardiac conducting system
Impulse travels from the SA node to the AV node Impulse conducted by internodal pathways Atrial contraction occurs AV node slows impulse Impulse travels from the AV node to the AV bundle © 2018 Pearson Education, Inc.

The Cardiac Cycle Summary of cardiac conducting system
The AV bundle conducts impulse along the interventricular septum and then divides to form the right and left bundle branches Serve right and left ventricle The bundle branches conduct impulses to the Purkinje fibers Purkinje fibers connect to cardiac muscle cells Ventricular contraction occurs © 2018 Pearson Education, Inc.

Components of the Conducting System Sinoatrial (SA) node contains pacemaker cells that initiate the electrical impulse that results in a heartbeat Internodal pathways are conducting fibers in the atrial wall that conduct the impulse to the AV node while simultaneously stimulating cardiac muscle cells of both atria Atrioventricular (AV) node slows the electrical impulse when it arrives from the internodal pathways AV bundle conducts the impulse from the AV node to the bundle branches Left bundle branch extends toward the apex of the heart and then radiates across the inner surface of the left ventricle Right bundle branch extends toward the apex of the heart and then radiates across the inner surface of the right ventricle Moderator band relays the stimulus through the ventricle to the papillary muscles, which tense the chordae tendineae before the ventricles contract Purkinje fibers convey the impulses very rapidly to the contractile cells of the ventricular myocardium © 2018 Pearson Education, Inc.

Movement of Electrical Impulses through the Conducting System 1 2 3 4 5 Time = 0 Elapsed time = 50 msec Elapsed time = 150 msec Elapsed time = 175 msec Elapsed time = 225 msec AV bundle Moderator band SA node AV node Bundle branches Purkinje fibers The SA node depolar- izes and atrial activa- tion begins. Depolarization spreads across the atrial surfaces and reaches the AV node. The AV node delays the spread of electrical activity to the AV bundle by 100 msecs. Atrial contraction begins. Impulses travel along the AV bundle within the interventricular septum to the apex of the heart. Impulses also spread to the papillary muscles of the right ventricle by the moderator band. The impulse is distributed by Purkinje fibers (subendocardial branches) and relayed throughout the ventricular myocardium. Atrial contraction is completed and ventricular contraction begins. © 2018 Pearson Education, Inc.

Atrial systole begins: Atrial contraction forces a small amount of blood into the relaxed ventricles. Start Atrial systole ends; atrial diastole begins: Atrial diastole continues until the start of the next cardiac cycle. 800 msec msec 100 msec Cardiac cycle Ventricular systole— first phase: Ventricular contraction pushes the AV valves closed but does not create enough pressure to open the semilunar valves. Ventricular diastole—late: All chambers are relaxed. The AV valves open and the ventricles fill passively. 370 msec Ventricular systole— second phase: As ventricular pressure rises and exceeds the pressure in the arteries, the semilunar valves open and blood is ejected. Ventricular diastole—early: As the ventricles relax, the ventricular blood pressure drops until reverse blood flow pushes the cusps of the semilunar valves together. Blood now flows into the relaxed atria. © 2018 Pearson Education, Inc.

Autonomic Control of Heart Rate
The SA node sets the heart rate but can be altered Impulses from the autonomic nervous system modify the pacemaker activity Nerves associated with the ANS innervate the: SA node AV node Cardiac cells Smooth muscles in the cardiac blood vessels © 2018 Pearson Education, Inc.

The effects of NE and ACh on nodal tissue Norepinephrine from the sympathetic division of the ANS causes: An increase in the heart rate An increase in the force of contractions Acetylcholine from the parasympathetic division of the ANS causes: A decrease in the heart rate A decrease in the force of contractions © 2018 Pearson Education, Inc.

Cardiac centers in the medulla oblongata modify heart rate Stimulation of cardioacceleratory center: activates sympathetic neurons Heart rate increases Stimulation of cardioinhibitory center: activates parasympathetic neurons Vagus (N X) is involved Heart rate decreases © 2018 Pearson Education, Inc.

Figure 21.12 The Autonomic Innervation of the Heart
Nucleus of vagus nerve Cardioinhibitory center Cardioacceleratory center Medulla oblongata Vagus nerve (X) Spinal cord Sympathetic Parasympathetic Parasympathetic preganglionic fiber Sympathetic preganglionic fiber Synapses in cardiac plexus Sympathetic ganglia (cervical ganglia and superior thoracic ganglia [ T1–T4]) Parasympathetic postganglionic fibers Sympathetic postganglionic fiber Cardiac nerve © 2018 Pearson Education, Inc.

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