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The transverse cardiac diameter varies with inspiration and expiration but normally should not exceed -?-One-half the diameter of the chest.
An apical pulse is palpable at the point of maximal impulse (PMI) in the -?-Fifth intercostals space just beneath the nipple.
Cardiac Features:
Landmark Location Contents
-?-Coronary sulcus Between atria and ventricles; nearly vertical behind sternum; Marks the annulus fibrosus that supports the valves Right side contains the right coronary artery; and small cardiac vein; crossed by anterior cardiac veins. Left side contains circumflex branch of the left coronary artery and coronary sinus.
-?-Anterior interventricular sulcus Between left and right ventricles. Marks the interventricular septum Contains the anterior interventricular branch of the left coronary artery and the great cardiac vein
-?-Posterior interventricular sulcus Delineates the interventricular septum, posteriorly Contains the posterior interventricular branch of the right coronary artery and the middle cardiac vein
Ventricular coronary flow occurs during ventricular diastole when a pressure differential occurs between the -?-Left ventricle and the aorta.
The papillary muscles take up the slack in the chordae tendineae to maintain the competence of the valvular closure as ventricular volume is reduced furing blood ejection. The valves close -?-Passively.
A ventricular septal defect produces a serious right-to-left shunt with cyanosis-"blue-baby" syndrome-because left ventricular pressure exceeds that in the right ventricle. A large VSD is the principal factor in -?-Tetralogy of Fallot.
Heart Valves
Valve Auscultation Comment
-?-Tricuspid Right of sternum in 6th intercostals space  
-?-Pulmonic Left of sternum over in 2nd intercostals space  
-?-Mitral Apex of heart in the 5th intercostals space in the left midclavicular line Insufficiency produces a low-pitched, late systolic blowing murmur
-?-Aortic Right of sternum over 2nd intercostals space Stenosis will tend to be ausculated as a high-pitched systolic murmur
The atrioventicular bundle passes through the annulus fibrosus and descends along the posterior border of the membranous part of the interventricular septum to enter the muscular portion of the septum. It transmits electrical activity to the -?-Ventricles.
Node Location Function Vasculature
-?-Sinoatrial In myocardium between crista terminalis and opening of superior vena cava Initiates contractile event with electrical depolarization spreading throughout atrial musculature Nodal branch of the right coronary artery
-?-Atrio-ventricula In the right atrial floor near the interatrial septum Stimulated by atrial depolarization: It leads into the atrioventricular (A-V) bundle to syncronize ventricular depolarization.  
Summary of autonomic pathways
Division Presynaptic Pathway Postsynaptic Pathway Effect
-?-Sympathetic From spinal levels T1-L2 along the ventral root; Reach the chain of sympathetic ganglia via white rami communicates 1.Fibers that synapse return to the spinal nerve via a gray ramus to mediate cutaneous piloerection, vasoconstriction, and sudomotor activity.
2. Fibers that do not synapse pass through the chain as splanchnic nerves to synapse In prevertebral ganglia; from these ganglia, postsynaptic neurons run in perivascular plexuses to innervate visceral target tissues.
Adrenergic neurotransmission increases heart rate, increases stroke volume, dilates coronary and pulmonary arteries
-?-Para-sympathetic Presynaptic cell bodies are located in the dorsal vagal nuclei of the brain. The myelinated synaptic axons form cranial nerve X, the vagus nerve Postganglionic cell bodies lie in numerous ganglia close to the target organ Cholinergic neurotransmission decreases heart rte, decreases stroke volume, and produces bronchoconstriction
Pain referral from thoracic viscera:
Organ Referral Area Pathway
Pericardial cavity T1-T5: Upper and mid thorax -?-Intercostal nerves T1-T5
Heart T1-T4: Upper thorax, postaxial brachium -?-Cervical and thoracic splanchnic nerves
Thoracic esophagus T1-T5: Thorax and epigastric region -?-Thoracic splanchnic nerves
Diaphragm Central Marginal C3-C5: Neck and Shoulder
T5-T10: Thorax
-?-Phrenic nerve
-?-Intercostal nerves
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