By C. Jensgar. Juniata College.
Epinephrine (high dose) order motilium 10 mg with mastercard, norepinephrine buy motilium discount, and tyramine all exert pressor effects via activation of (Xl receptors discount motilium online mastercard. However discount motilium 10 mg without a prescription, only epinephrine is active on ~2 receptors, and this action would be revealed by vasodilation and a reversal of its pressor effects following treatment with an alpha blocker-"epinephrine reversaL" Thus, drug #4 can be identified as epinephrine. Mydriasis and fixed far vision can be due to either muscarinic receptor antagonists or ganglionic blockade. The cholinesterase inhibitor (neostigmine) and alpha blocker (phentolaminelcause miosis. Ocular effects of the beta blocker (timolol) are restricted to decreased formation of aqueous humor by the ciliary epithelium. Mydriasis is associated with blockade of M receptors, and both micturition and sweating result from activation of such receptors. However, reflex bradycardia is not possible following pretreatment with an M blocker. This question is to remind you that indirect-acting sympathomimetics require innervation of the effector organ to exert effects. However, transplanted hearts retain receptors, including those (~l) responsive to direct-acting sympathomimetics. If symptoms improve with a single dose of edrophonium, then an increase in the dose of neostigmine or pyridostigmine is indicated. The effectiveness of labetalol in the management of hypertension and in severe hypertensive states appears to be due to a combination of antagonistic actions at both alpha and beta adrenoceptors. Labetalol is not a ~l selective blocking agent (unlike atenolol and metoprolol), and (unlike pindolol and acebutolol) it lacks intrinsic sympa- thomimetic activity. Labetalol is available for both peroral and parenteral use; unfortu- nately, it blocks ~2 receptors in bronchiolar smooth muscle. Only two of the listed drugs directly activate cardiac receptors: epinephrine and norepinephrine. This could occur only if agonist 3 was capable of ~l receptor activation in the heart. Direct cardiac stimulation could occur with norepinephrine (agonist 3) but not with methoxamine (agonist 2), which is a selective alpha adrenoceptor agonist. Explanations to Figures 11-4-2 through 11-4-11: Drug Identification from Effects on Heart Rate and Blood Pressure. Figure 11-4-2: The effects of Drug R are changed by treatment with either an alpha or beta- blocker, so Drug R must have activity at both receptors (choices C, D, and E are ruled out). A pressor dose of epinephrine would be "reversed" by an alpha- blocker, not just decreased! Figure 11-4-3: The effects of Drug U are changed by treatment with the alpha-blocker, but not by the beta-blocker. Drug U must be an alpha-activator with no beta actions-the only choice is phenylephrine. Figure 11-4-4: The effects of Drug S are changed by treatment with the beta-blocker, but not by the alpha blocker (choices A, B, and C are ruled out). Note that option A would have been a possibility but one would have to assume a low-dose of epinephrine. Figure 11-4-5: The effects of Drug H are changed by treatment with either an alpha- or beta- blocker, so Drug H must have activity at both receptors (choices C, D, and E are ruled out). Figure 11-4-6: Mecamylamine blocked reflexed tachycardia induced by Drug X, which dropped blood pressure by vasodilation. Note that the alpha agonist does not antagonize the decrease in respiratory resistance (a ~2 response). Because Drug X abolishes only the reflex tachycardia, it must be the ganglion blocker hexame- thonium (choice A). Arterial con- traction due to the alpha agonist (choice E) is reversed by the alpha-blocker (choice C). Arteriolar relaxation and tachycardia due to epinephrine (choice B) is reversed by the beta-blocker (choice D). Figure 11-4-10: Classic example showing that denervated tissues do not respond to indirect- acting agonists. In this case, tyramine fails to cause mydriasis in the left eye, but this eye is more responsive than the right eye to epinephrine (denervation supersensitivity). Tachycardia due to Drug R is unaffected by any antagonist, indicative of a beta activator (choice D). Rate of depolarization depends on number of Na" channels open, which in turn depends on resting membrane potential of the cell. In some His-Purkinje cells, transient outward K+ currents and inward cr currents contribute to the "notch" and overshoot. Phase 3 • Repolarization phase in which the delayed rectifier K+ current rapidly increases as the Caz+ current dies out because of time-dependent channel inactivation. Note that during phases 0 through 3 a slow Na" current ("window current") occurs, which can help prolong the duration of the action potential. Conductance Rate of spread of an impulse, or conduction velocity-three major determinants: Rate of phase 0 depolarization-as Vmax decreases, conduction velocity decreases and vice versa. Fundamental Concepts No appreciable Na+ current during phase 0 in these cells because the Na channels are either absent or in an inactive form because of the existing voltage. During repolarization, the Ca2+ currents are opposed and overcome by the delayed rectifier K+ current. The relative magnitudes of these opposing currents determine the "shape" of the action potential. Automaticity The ability to depolarize spontaneously confers automaticity on a tissue. Refractoriness • The inability to respond to a stimulus-property of all cardiac cells. Inactivation of the h gate is slower; therefore, it stays open longer and the Na channel is active. Rate of recovery is slower in ischemic tissue because cells may be partly depolarized at rest. This reduces the number of channels able to participate in the next depolariza- tion, which leads to a decrease in conduction rate in ischemic tissue. Chapter Summary The sequences of ionic events in the action potential of cardiac cells are described. Responsivity, capacity of a cell for depolarization, depends on resting membrane potential; con- ductance is the rate of potential spread; refractoriness is the inability to respond to excitation. Three conformations exist-resting (ready), active (open), and inactive (refractory). Class I drugs are least active when Na" channels are in the resting state (state-dependent actions). This results in an increased threshold for excitation and less excitability of hypoxic heart muscle. The uses for lidocaine, mexiletine, and tocainide are discussed, as are the metabolism and adverse effects of lidocaine. However, homeostatic mechanisms may lead to compensatory increases in heart rate and/or salt and water retention. The metabolic characteristics, clinical uses, and potential adverse effects of sympathoplegic drugs, which decrease peripheral resistance by decreasing sympathetic tone, are discussed. Sympathoplegic drugs also may act directly as adrenergic neuron blockers, alpha blockers, or beta blockers. Direct-acting vasodilators lower the peripheral vascular resistance mainly by causing arteriolar dilation. Figure 111-3-2illustrates the angiotensin system and the pharmacologic effects of these drugs. Digoxin has potential toxic effects that are in part dependent upon the electrolyte balance. Bipyridines, sympathomimetics, diuretics, beta blockers, and nesiritide also have uses in treating heart failure. Beta blockers act directly on the heart by decreasing the heart rate, the force of contraction, and cardiac output, thereby decreasing the work performed. Actions of Diuretics at the Various Renal Tubular Segments Hypokalemia and Alkalosis Diuretics that block Na+ reabsorption at segments above the collecting ducts will increase sodium load to the collecting tubules and ducts ("downstream").
A stress-induced heart condition called stress cardiomyopathy (broken heart syndrome) has only recently been clearly identiﬁed by Western medicine purchase motilium 10 mg amex. The syndrome occurs most frequently after a sudden intense emotional trauma such as death in the family best purchase for motilium, an experience of violence motilium 10 mg low price, or extreme anger discount motilium online. The symptoms are similar to an acute heart attack, but the coronary arteries are found to be normal and the heart tissue is not damaged. It has suggested that the condition is triggered by an excessive release of stress-related hormones called chatecholamines. During the period of ﬂow, the velocity of the blood is about three times as high as the overall average value calculated in Exercise 8-6. The kinetic energy in the smaller arteries is even less because, as the arteries branch, the overall area increases and, therefore, the ﬂow velocity decreases. For example, when the total ﬂow rate is 5 liter/min, the blood velocity in the capillaries is only about 0. The kinetic energy of the blood becomes more signiﬁcant as the rate of blood ﬂow increases. For example, if during physical activity the ﬂow rate increases to 25 liter/min, the kinetic energy of the blood is 83,300 erg/cm3, which is equivalent to a pressure of 62. This energy is no longer neg- ligible compared to the blood pressure measured at rest. In healthy arteries, the increased velocity of blood ﬂow during physical activity does not present a problem. During intense activity, the blood pressure rises to compensate for the pressure drop. Assuming a Reynold’s number of 2000, the critical velocity for the onset of turbulence in the 2-cm-diameter aorta is, from Eq. But as the level of physical activity increases, the ﬂow in the aorta may exceed the critical rate and become turbulent. In the other parts of the body, however, the ﬂow remains laminar unless the passages are abnormally constricted. Laminar ﬂow is quiet, but turbulent ﬂow produces noises due to vibrations of the various surrounding tissues, which indicate abnormalities in the circu- latory system. These noises, called bruit, can be detected by a stethoscope and can help in the diagnosis of circulatory disorders. In the United States, an estimated 200,000 people die annually as a consequence of this disease. In arteriosclerosis, the arterial wall becomes thickened, and the artery is narrowed by deposits called plaque. Sixty to seventy percent is considered severe, and a narrowing above 80% is deemed critical. If, for example, the radius of the artery is narrowed by a factor of 3, the cross-sectional area decreases by a factor of 9, which results in a nine-fold increase in velocity. The increased kinetic energy is at the expense of the blood pressure; that is, in order to maintain the ﬂow rate at the higher velocity, the potential energy due to pressure is converted to kinetic energy. For example, if in the unobstructed artery the ﬂow velocity is 50 cm/sec, then in the constricted region, where the area is reduced by a factor of 9, the velocity is 450 cm/sec. Because of the low pressure inside the artery, the external pressure may actually close oﬀ the artery and block the ﬂow of blood. When such a blockage occurs in the coronary artery, which supplies blood to the heart muscle, the heart stops functioning. Stenosis above 80% is considered critical because at this point the blood ﬂow usually becomes turbulent with inherently larger energy dissipation than is associated with laminar ﬂow. As a result, the pressure drop in the situa- tion presented earlier is even larger than calculated using Bernoulli’s equation. Further, turbulent ﬂow can damage the circulatory system because parts of the ﬂow are directed toward the artery wall rather than parallel to it, as in laminar 112 Chapter 8 The Motion of Fluids ﬂow. The blood impinging on the arterial wall may dislodge some of the plaque deposit which downstream may clog a narrower part of the artery. If such clogging occurs in a cervical artery, blood ﬂow to some part of the brain is interrupted causing an ischemic stroke. The artery has a speciﬁc elasticity; therefore, it exhibits certain springlike prop- erties. Speciﬁcally, in analogy with a spring, the artery has a natural fre- quency at which it can be readily set into vibrational motion. Deposits of plaque cause an increase in the mass of the arterial wall and a decrease in its elasticity. As a result, the natural frequency of the artery is signiﬁcantly decreased, often down to a few hundred hertz. The plaque- coated artery with its lowered natural frequency may now be set into resonant vibrational motion, which may dislodge plaque deposits or cause further dam- age to the arterial wall. We will now compute the power generated by the heart to keep the blood ﬂowing in the circulatory system. Therefore, as shown in Exercise 8-10, the power output of the right ventricle is 0. While in fact the systolic blood pressure rises with increa- sed blood ﬂow, in these calculations we have assumed that it remains at 120 torr. Both abnormally high and abnormally low blood pressures indicate some disorders in the body that require medical attention. High blood pres- sure, which may be caused by constrictions in the circulatory system, certainly implies that the heart is working harder than usual and that it may be endan- gered by the excess load. Blood pressure can be measured most directly by inserting a vertical glass tube into an artery and observing the height to which the blood rises (see Fig. This was, in fact, the way blood pressure was ﬁrst measured in 1733 by Reverend Stephen Hales, who connected a long ver- tical glass tube to an artery of a horse. Although sophisticated modiﬁcations of this technique are still used in special cases, this method is obviously not satisfactory for routine clinical examinations. Routine measurements of blood pressure are now most commonly performed by the cut-oﬀ method. Although this method is not as accurate as direct measurements, it is simple and in most cases adequate. In this technique, a cuﬀ containing an inﬂatable balloon is placed tightly around the upper arm. The balloon is inﬂated with a bulb, and the pressure in the balloon is monitored by a pressure gauge. The initial pres- sure in the balloon is greater than the systolic pressure, and the ﬂow of blood through the artery is therefore cut oﬀ. The observer then allows the pressure in the balloon to fall slowly by releasing some of the air. As the pressure drops, she listens with a stethoscope placed over the artery downstream from the cuﬀ. No sound is heard until the pressure in the balloon decreases to the systolic pressure. Just below this point the blood begins to ﬂow through the artery; however, since the artery is still partially constricted, the ﬂow is turbulent and is accompanied by a characteristic sound. As the pressure in the balloon drops further, the artery expands to its normal size, the ﬂow becomes laminar, and the noise disappears. The pressure at which the sound begins to fade is taken as the diastolic pressure. The cut-oﬀ blood pressure measurement is taken with the cuﬀ placed on the arm approximately at heart level. Calculate the pressure drop per centimeter length of the aorta when the blood ﬂow rate is 25 liter/min. The radius of the aorta is about 1 cm, and the coeﬃcient of viscosity of blood is 4 × 10−2 poise. Compute the average velocity of the blood in the aorta of radius 1 cm if the ﬂow rate is 5 liter/min. When the rate of blood ﬂow in the aorta is 5 liter/min, the velocity of the blood in the capillaries is about 0.
Perhaps the pain is actually caused by bacteria living in the blocked bile ducts and invading the shoulder 10mg motilium for sale. Magnets of high strength (2x5000 gauss) taped to your arm generic motilium 10 mg with amex, under your sleeve purchase 10mg motilium amex, can get you through the day cheap generic motilium canada. If not, you should wait several days before trying again; this time avoid pain killers the day of the cleanse. Peggy Patton, age 60, had shoulder pain and painful feet in addition to aching all over. She started gardening again and immediately picked up hookworms and Trichinella again. But she learned to sanitize her hands with grain alcohol after washing away dirt and this kept her parasites in check. Jessica Atkinson, a middle age school teacher, developed a pain in the right cheek quite suddenly. She also had pain over the right mid abdomen and right side at the waist but X-rays and scans showed nothing (she had been X-rayed three times). She was having severe pain attacks over the liver and described her stool as almost white after these attacks. She cleaned her liver at least 30 times before she related, one day, that her joy in living had returned. Eventually the abscesses in her upper teeth were found, clearing up her cheek pain and protecting the liver from recurrent infections from these bacteria. She could also stop using Tums , stop coughing, and no longer was bothered by her hiatal hernia. Elbow Pain One variety of elbow pain is due to an inflamed tendon there; it is sometimes called “tennis elbow. The inflammation is caused by a liver full of stones and parasites, especially flukes which manufacture a chemical that affects tendons. Using your elbows while they are inflamed is traumatic to them, like working with a sore thumb. Wrist Pain Tendons passing through the wrist can become inflamed from the unnatural chemicals produced by fluke parasites in the liver. Using the wrists to work further traumatizes them (injures them) making it harder for them to heal. A small hole between the tendons lets the nerve and blood vessels through into the hand. When tendons at the wrist thicken, they can squeeze down on the nerves and blood vessels until the hand or fingers feel numb. Wearing a wrist bandage or support can help reduce trauma damage to the wrist while it is healing. Numbness of hands, without wrist pain, is more often due to a brain problem with parasites and pollutants. If the pain goes away beforehand, while you are on the kidney cleanse, it shows you had deposits in your joints. Finger Pain This is pain in a joint, often accompanied by some enlarge- ment or knobbyness of the joint. It is not hard to recognize these as deposits of the same kind as we saw in the toes. In six weeks after starting the kidney cleanse and changing your diet, the knobs may already be shrinking. A large magnet (5000 gauss—used only as directed) may bring pain relief but only dental cleanup and environmental cleanup will give you lasting improvement. Pulling an infected tooth or cleaning a cavitation can bring complete relief, only to return the next time a tooth is extracted. Cleaning the liver can also bring immediate relief, only to find pain and stiffness to return months later. An allergic reaction to potatoes and tomatoes can express it- self in neck pain too. Perhaps they prefer to attach themselves at a particular neck site and cause inflammation here. Whiplash is often blamed for back-neck pain and indeed chiropractic ad- justments can bring total relief. Front Neck Pain Lymph nodes under the jaw strain your body fluids of the head, removing bacteria and toxins. Roland Sanford, 23, had minor pain and a lot of stiffness along the sides of his neck. He only had one metal tooth filling but his whole body was toxic with samarium, be- ryllium, indium, copper, cesium, and mercury. Audrey Doyle had severe neck pains she attributed to sitting all day and sleeping in her wheelchair. She knew eating cream and butter made it worse but she had no will power, she said. Ask the dentist to search for hidden tooth in- fections and to clean your cavitations (you will need to find an alternative dentist, and read Dental Cleanup, page 409). Begin immediately to heal these bone lesions with vitamin D (40,000 to 50,000 units once a day for 3 weeks, followed by 2 such doses per week forever), milk-consumption for calcium, and a magnesium oxide tablet. For extra muscle relaxation, take two magnesium tablets at bedtime and valerian capsules. Tooth Ache Before the pain becomes acute and excruciating, kill bacteria of the mouth, including “tooth decay” and “tooth plaque” frequencies (see frequency list, page 561). If zapping bacteria several times in a few hours relieves pain enough to get you through the night or past the weekend, do not delay a single day. Zapping does not reach into the middle of an abscess—it circles around, so some bacteria are left to repopulate. Removing them always helps and may let the jaw heal normally where they were extracted. Since the pain is caused by a bulging infection pressing on a jaw nerve, and because each tooth has a related organ(s) it is especially important to clear up all infections to protect these organs. Finding that teeth have the same tissue frequency as some distant organ sheds a little light on the situation. Until the meaning and function of these frequencies is understood we can only guess that they interact somehow. Bacteria have taken advantage of this common resonance and have invaded both organs. It is a common heart bacterium, causing much of our heart ailments, particularly mitral valve disease and irregularity problems. After wisdom teeth are extracted, the hole left in the jaw frequently does not heal, it picks up Staphylococcus aureus from the mouth and a chronic infection is started. Pain and body damage will return unless you do the proper re- pair and cleanup work. Throat Pain Recurring sore throats are always improved by removing dental metal and root canals, and by cleaning up hidden tooth infections. Bacteria and viruses that cause sore throats are thriving in hiding places under and around dental metal. It is quite difficult to reach the center of such places (abscesses) with electric currents. Even if you could, you would reinfect the very next time you ate non- sterile food! The eye is a favorite location for many para- sites, including Giardia, amoebas, hookworm, schistosomes, Toxoplasma, and innu- merable others. The eye has two large bodies of watery fluid: the aqueous humor and vitreous humor, where no blood Light travels through the cornea, through traverses to bring in extra the aqueous liquid, the lens, and then the white blood cells when vast vitreous humor, finally striking the the need arises. It has its super sensitive spot on the retina, called own protective devices, the macula. Toxoplasma infection could be the beginning of a lifetime of eye disease due to weakening of the eyes at an early age. Toxoplasma also invades the brain, frequently causing a dull ache or pressure at the back of the head. By killing all the large parasites plus a few bacteria (Staphylococci, Chlamydias, Neisserias) the eye can become pain free in a few days.
The tricuspid valve has a similar purpose but is a less effective valve than the mitral because of its more complex structure order 10 mg motilium with visa. Fortunately buy motilium with american express, it performs under about 1/3 – 1/4 of the pressure demands of the left side of the heart order motilium 10mg otc. The papillary muscle within the right ventricle varies in size from the large anterior single papillary muscle which supports the commissure between the anterior and posterior leaflets discount motilium 10mg overnight delivery, to the posterior papillary group having 2 –3 beats and supporting the commissure between the posterior and anterior leaflet. A separate muscle within the outlet of the right ventricle (Muscle of Lancisi) supports the anterior septal cusps of the tricuspid valve. Additional small supports of the septal leaflet arise from direct septal chordae tendineae. These will be referred to again in connection to the architecture of the right ventricle. The aortic and pulmonary valves are similar in structure, having 3 leaflets or cusps. When seen side-on they look like half moons and are therefore termed semilunar valves. They are attached to the underlying ventricular muscle at the base, and to the aortic root above. In their midline each aortic cusp has a central little nodule (Nodule of Aranantius). The aortic valve is a little thicker than the pulmonary valve and coronary arterial ostia arise from it. The aortic cusps facing the pulmonary artery each give rise within the sinuses of Valsalva to a coronary artery. The left Introduction To Cardiac & Tomographic Anatomy Of The Heart - Norman Silverman, M. There is no coronary artery arising from the posterior cusp, which is in continuity with the anterior leaflet of the mitral valve. The conventional manner for defining the structures is by examining the heart morphologically along the lines of flow. The surface of the right atrium, (slide 9-11), shows a large appendage with a broad base connected to the rest of the atrium. First the muscular bundles called the pectinate muscles (comb-like) are seen to come from the right atrial appendage and spread themselves over the vestibule of the right atrium (the portion proximal to the tricuspid valve). The smooth part of the atrium lying between the veins is called the sinus intervenarum (lake between the veins). As one looks at the atrial septum medially (remember, we are opening this atrium from the right side of the body) one identifies an oval depression - the fossa ovalis. This area is the place where fetal communication between the atria existed, allowing oxygen-rich umbilical venous blood to be shunted away from the right ventricle and across into the left atrium. From there the blood flows to the important fetal structures, the brain and heart. As this is a thin membranous rather than muscular structure, it is often possible to illuminate it by shining a light from the left atrium to define its extent. It is notable that the true area of communication of the atrial septum is only a little larger than this structure, and that other structures which appear on the medial aspect lie outside the confines of the septum. The upper orifice in the sinus intervenarum is the entrance of the superior vena cava and the lower orifice is the inferior vena cava. There is another orifice in the medial aspect of the atrium adjacent to the tricuspid valve, situated below and marking the exit point of the atrium. The Eustachian valve and the valve of the coronary sinus (Thebesian valve), join to form the tendon of Todaro. This, together with the tricuspid septal leaflet, makes up a triangular area (the triangle of Koch) an area that contains the atrioventricular node so important for cardiac conduction. At the upper end of the atrium between the superior vena cava and the atrial appendage lies a thick ridge of muscle called the Crista Terminalis (Terminal Crest) It is the muscular ridge between the sinus intervenarum and the true atrium. At the upper end of this ridge is the area of the sinus node which drives automatic cardiac electrical activity through specialized Purkinje cells. This area is on the right valve of the sinus venosus and its extension the Eustachian valve. The left valve of the sinus venosus forms the thick ridge or limbus of the fossa ovalis. There is a large muscle running in the anterior groove between the inlet and outlet sections of the ventricles. It arises under the pulmonary valve superiorly and travels between the junctions of the anterior wall with the ventricle Introduction To Cardiac & Tomographic Anatomy Of The Heart - Norman Silverman, M. In some texts those who believe that it moderated over expansion of the right ventricle refer it to as the moderator band. Running over the top of the ventricle, between the pulmonary valve and at right angles to the septal band, is a structure termed the ventricular infundibular fold (because it runs between the outlet of the right ventricle termed the infundibulum) or the parietal band of the Crista, (crest above the ventricle). Thus, for some morphologists, there is a Crista supraventricularis (crest above the ventricle) with a septal or a parietal band. I prefer that these be called the septomarginal trabeculation and the ventricular infundibular fold. The septomarginal trabeculation is also an anatomic and embryologic landmark between the inlet and the outlet of the ventricle. It gives direct rise from the right ventricle to all the papillary muscles of the right ventricle, including the chordae tendineae. As the ventriculoinfundibular fold is muscular, there is no connection between the tricuspid and pulmonary valve. The ventricles are tripartite, all containing sections defined most clearly from the ventricular septum discussed below. These are the inlet, muscular (or trabecular) and outlet positions of both ventricles. With regard to the left side of the heart, when viewed from the left side, the small finger-like left atrial appendage is seen anteriorly, and the entrance of the left pulmonary veins posteriorly. The lower border of the appendage is crenulated and its attachment to the body of the left atrium is narrow. The pectinate muscles of this atrium are much finer than its fellow on the right side, and do not extend out of the atrial appendage as its fellow on the right side does. The left atrial aspect of the atrial septum can be illuminated to demonstrate the thin septum primum which has a horseshoe curve. The left ventricle has two papillary muscles attached to the inferior and lateral walls and the septum is free of attachment of papillary muscles. The anterior leaflet of the mitral valve is in fibrous attachment with the non-coronary cusp of the aortic valve. The lack of septal attachment of the mitral valve and the fibrous continuity of the anterior mitral valve leaflet to the non-coronary cusp are two distinctive differences between the left and right ventricle. The septal surface of the left ventricle and its right-sided fellow form the smooth upper septal surface and fine apical trabeculations. Because of pressure differences the left ventricle is also thicker walled than the right ventricle. As noted previously, the ventricle can be divided into inlet, trabecular and outlet portions. There is a fourth component - the membranous septum - a little fibrous tissue lying under the aortic valve between the right and non-coronary cusps when seen on the left side, and just under the septal leaflet of the tricuspid valve when viewed from the right side. In slide 12, the conduction system of the heart contains cellular and fibrous elements. The automatic firing comes from the cellular elements within the sinoatrial and atrioventricular nodes, and also within the upper cells lying within the His–Purkinje system. A hierarchical firing is present where the faster rates lie within the highest (sinoatrial) area and the periodicity decreases as the Introduction To Cardiac & Tomographic Anatomy Of The Heart - Norman Silverman, M. The sinoatrial node is a small cigar- shaped structure lying between the atrial appendage and the superior cava almost on the surface of the heart. There are no actual connections between the two nodes, although the fibers tend to run in the areas between the appendages and vascular entry. The atrioventricular node lies within the triangle of Koch and then penetrates above the muscular and below the membranous septum, where it runs on the left ventricular septal surface for a small distance. As the bundle divides the right bundle runs back toward the right ventricle, perforating near the muscle of Lancisi within the right ventricle and then running toward the right ventricular apex under the septomarginal trabeculation. These bundles are also apically directed and enter in the papillary muscles from the apical route to terminate within these muscles. The left main coronary artery has a short course and divides into a left anterior descending coronary artery and a circumflex.