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Physiology Ch. 10
Cardiac Muscle
| Term | Definition |
|---|---|
| Cardiac muscle is | Involuntary and autorhythmic |
| Endocardium | Simple squamous epithelium w/ areolar ct |
| Myocardium | Cardiac muscle, contracts to pump blood |
| Epicardium | Continuous lining of blood vessels |
| Interatrial septum | Separates L&R atrium |
| Interventricular septum | Separates L&R ventricles |
| R atrium | Contains pectinate muscles and fossa ovalis. Top right anatomically. |
| Pectinate muscles | Ridges in anterior wall and within auricle of R atrium |
| Fossa ovalis | Oval depression on R atrial part of interatrial septum that closes during development ('hole in heart') |
| RMP of cardiac muscle | -60mV |
| Resting heart rate, due to ___. | 70-75 bpm, parasympathetic nervous system |
| Innervation to the heart _____, not initiates cardiac activity. | Modifies |
| R ventricle | Has trabeculae carneae, 3 papillary muscles, and tendinous cords (cordae tendineae). Bottom left anatomically. |
| Trabeculae carneae | Irregular muscular ridges inside ventricle wall |
| Papillary muscles | Cone-shaped projections extending from internal ventricle wall that anchors tendinous cords. R ventricle has 3, L has 2. |
| Tendinous cords | Also called cordae tendineae. Thins strands of collagen fibers attached to AV valve. |
| L atrium | Pectinate muscles in auricle, exits to L ventricle through left AV valve. Top left anatomically. |
| L ventricle | Has 2 papillary muscles, superior exit to aorta through aortic semilunar valve. Bottom left anatomically. |
| AV valves | Prevent backflow into atria, close when ventricles contract |
| R AV valve | Tricuspid |
| L AV valve | Bicuspid, mitral |
| Semilunar valves | Prevent backflow to ventricles, open when ventricles contract and blood goes to arteries, close when ventricles contract |
| Pulmonary semilunar valve | Between R ventricle and pulmonary trunk. |
| Aortic semilunar valve | Located between L ventricle and the aorta |
| Cardiac mucle cells connect through _____, form a _____, and are ____ than skeletal muscle cells. | Intercalated discs, syncytium, smaller |
| Cardiac muscle cells have __ central nucleus and have ____ mitochondria than skeletal muscle. | 1, more. |
| Desmosomes | Mechanically join cells with protein filaments in cardiac cells. |
| Gap junctions | Electrically join cells to make each heart chamber a functional syncytium, which is critical to heart's ability to be electrically coupled. |
| Carbiomyocytes | High demand for energy, have myoglobin and creatine kinase, and relies mostly on aerobic metabolism. |
| Cardiomyocytes are susceptible to failure when _______. | Ischemic (when O2 is low). |
| Conduction system | Initiates and conducts electrical events to ensure proper timing of contractions. |
| AV node | Near R AV valve. |
| SA node | Natural pacemaker |
| AV bundle | Divides into L&R, extends from AV node through interventricular septum. |
| Purkinje fibers | Extend from L&R bundles at heart's apex, goes through walls of ventricles. |
| Cardia center | Part of medulla oblongata which modifies (NOT INITIATES) cardiac activity. |
| Parasympathetic innervation ____ heart rate, _____ medulla's cardio-inhibitory center. | Decreases, starts. |
| Sympathetic innervation _____ heart rate and ____ of contraction, _____ medulla's cadio-acceleratory center. | Increases, force, starts. |
| Nodal cells | In SA node, initiates heart beat |
| RMP of nodal cells is _____, but cells _____ have stable RMP. | -60mV, do not |
| SA node cells | Slow depolarization (S <-> S) |
| Automaticity (Auto-rhythmicity) | Nodal cells can stimulate their own action potentials without an action potential from a neuron |
| Steps of auto-rhythmicity: | 1. Reaching threshold (Slow Na+ channels open, RMP from -60 to -40mV) 2. Depolarization (Fast Ca2+ channels open, mp from -40 to +5mV) 3. Repolarization (Ca2+channels close, K+ open) |
| What is threshold for nodal cells? | -40mV |
| Action potential of nodal cell steps: | 1. Na+ inflow via leak 2. Ca2+ inflow after threshold 3. K+ outflow 4. Repolarizaiton |
| Pacemaker potential | Ability to reach threshold without stimulation (in nodal cells) |
| Nodal cells are _____ going through the action potential cycle. | Always |
| Vagal tone | Parasympathetic cranial nerve which makes heart beat around 70bpm instead of 100 |
| Atria contract _______. | Together |
| Ectopic | Conduction system cells for pacemaking other than SA node, depolarize at slower rates than SA |
| Action potential pathway through heart: | SA node -> thru atria (both contract together) -> AV node, delays so ventricles can fill -> AV bundle -> bundle branches -> Purkinje fibers -> spread through ventricles |
| Purkinje fibers of ventricles are _____ in diameter and have a super ______ action potential. | Larger, rapid |
| Papillary muscles in ventricles are stimulated to contract ______. | Immediately |
| In the ventricles, stimulation begins at the heart's _____, ensuring _______. | Apex, blood efficiently ejects toward atrial trunks |
| The _____ is the default pacemaker if SA fails | AV node (40 or so bpm) |
| Resting potential of cardiomyocites | -90mV |
| Threshold for cardiomyocites | -65mV |
| Types of channels in cardiomyocites: | Fast volt-gated Na+ channels, slow volt-gated Ca2+ channels, volt-gate K+ channels. All 3 are closed when cell is at rest. Also has Na+/K+ pumps, Ca2+ pumps, and leak Na+ and K+ channels |
| Action potential steps in cardiac muscle: | 1. @T tubule. Na+ enters 2. L-type Ca2+ channels open to let in small amount of Ca2+ 3. Ca2+ triggers Ca2+ channels in sarcoplasmic reticulum by binding to ryanodine receptor 4. Cross bridge cycle 5.Ca2+-ATPase return Ca2+ to reticulum 6. K+ outflow |
| Electrical events of action potential of cardiac muscle: | 1. Depolarization - -90 to +30mV (RAPID spike) 2. Plateau - depolarization opens K+ and slow Ca2+ channels (is still depolarized) 3. Repolarization- Ca2+ close while K+ stay open. Efflux of K+> influx of Ca2+ |
| Cardiac muscle, unlike skeletal muscle, ______ experience tetany. | Cannot |
| Cardiac muscle has a ____ refractory period, unlike skeletal muscle. | Long |
| ECF Ca2+ ______ for contraction of skeletal muscle, but in cardiac muscle ______. | Is not required, it is |
| The _____ the amount of Ca2+, the force of contraction of CARDIAC MUSCLE _____. | Greater, increases |
| Absolute action potential of cardiac muscle (cardiomyocytes, not nerves) | 250ms |
| How does skeletal muscle increase its force? How does cardiac muscle? | Via recruitment. Cardiac muscle is always working and cannot recruit, but more Ca2+ released to cytosol will increase force of contraction. |
| _______ and ______ horomones allow _______ Ca2+ into the cytosol. | Norepinephrine, epinephrine, increased |
| Positive intropy | Caused by increased Ca2+ in cytosol, is increased force of contraction |
| Positive chronotrophy | Increase in frequency of contraction (greater HR). Increases with more Ca2+ |
| Cardiac cycle | All events in heart from start of a beat to the next |
| Systole | Contraction, increased pressure |
| Diastole | Relaxation |
| The diastole is normally _____ as ______ as the systole. | 2x, long |
| Ventricular filling | In late diastole, where semilunar valves are closed, AV valves are open, and blood flows from atria to ventricles. |
| When ventricles contract, AV valves _____ and semilunar ____ due to the ______ of pressure. | Close, open, increase |
| End-diastolic volume (EDV) | Volume of blood when ventricles are filled |
| Stroke volume (SV) | Amount of blood ejected by ventricle |
| End systolic volume (ESV) | Amount of blood remaining in ventricle after contraction finishes |
| Equation to calculate ESV and example values: | ESV = EDV - SV 60mL = 130mL - 70mL |
| Isovolumetric | Where all valves of heart are closed and blood neither enters or exits |
| Isovolumetric contraction | Initiated by purkinje fibers. Ventricles contract and AV valves close, but P isn't high enough to open semilunar |
| Isovolumetric relaxation | Ventricles relax and P decreases. Arterial P > ventricular P and AV valves remain close and semilunar close. |
| _____ of blood filling the ventricles happens before arterial contraction. | 80% |
| Cardiac output (CO) | Amount of blood pumped by a SINGLE ventricle in one minute (measured in L/min) |
| Equation of CO: | CO = HR times SV |
| Left ventricle _____ completely empty during systole | Does not |
| Ejection fraction (EF) | Measured by echocardiogram, how much blood is ejected per contraction |
| Normal EF | 62mL |
| Equation for EF | EF = SV/EDV |
| The greater the contractility, the ____ the EF. | Greater |
| Cardiac reserve | Capacity to increase CO above rest level (Ex: in exercise) |
| Inherent HR (sympathetic innervation) | 100 bpm |
| Chronotropic agents | Agents that change HR via altering activity of nodal cells. Positive ones increase HR (Caffine, NE, sympathetic innervation), negative decrease (parasympathetic) |
| Normal SV | 70mL |
| Venous return | Volume of blood returned to the heart; related directly to SV, determines preload and amount of blood prior to contraction. |
| Frank-Starling Law | As EDV increases, the heart wall stretches more, so the heart will contract harder (because it will fill with more blood) |
| Preload | Ventricular filling pressure, degree to which cardiac muscle cells are stretched before they contract. |
| The greater the preload, the _____ the SV. | Greater |
| Afterload | Blood pressure, pressure ventricles must overcome to force open aortic and pulmonary valves. |
| The greater the afterload, the ____ the SV. | Less |
| Bradycardia | Low resting HR in adults, natural in athletes |
| Tachycardia | Persistently high resting HR |
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