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boundaries of the superior mediastinum
extends from superior thoracic aperture to transverse thoracic plane (sternal angle to IV disc between T4/T5)
boundaries of the inferior mediastinum
transverse thoracic plane to diaphragm
boundaries of the subdivisions of the inferior mediastinum
- -anterior: between pericardium and sternum
- -posterior: between pericardium and anterior portion of vertebral bodies (T5-T12)
- -middle: location of the heart
functions of the pericardium
- -Prevents infection spreading
- -Limits size of the heart (limits gross acute distention); protects against overfilling of heart chambers and overstretching of cardiac muscle
- -Diastolic coupling
Describe the walls of the four chambers...
- R Atrium- smooth/thin posterior wall and rough/muscular anterior wall
- L Atrium- smooth walled
- L Ventricle- thick walls
Location of the chambers...
- L Atrium- base of the heart
- R Ventricle- anterior/inferior surface of heart
- L Ventricle- apex of heart
Atria vs. Ventricles
- Atria- have auricles and pectinate muscles
- Ventricles- trabeculae carneae
Unique features of each chamber...
- R Atrium: sulcus terminalis and fossa ovalis
- R Ventricle: conus arteriosus and moderator band
Trace a drop of blood.
superior and inferior vena cavae, right atrium, tricuspid valve, right ventricle, pulmonic valve, pulmonary arteries, lungs, pulmonary veins, left atrium, bicuspid valve, left ventricle, aortic valve, aorta, body...
What chambers contract with an impulse initiated at the SA node?
left and right atria
What anatomical feature of the heart prevents the SA node from causing direct ventricular contraction? Why doesn’t the entire heart contract with the SA node?
Fibrous Skeleton of the Heart; The fibrous skeleton acts as an electrical insulator between the atria and ventricles, facilitating their independent contraction.
Left bundle branch innervates...
IVS, papillary muscles and walls of left ventricle
Right bundle branch innervates...
IVS, moderator band, papillary muscles, and walls of right ventricle
Where do the postsynaptic sympathetic fibers begin and end?
Postsynaptic sympathetic fibers originate in upper thoracic and cervical ganglia of sympathetic trunks, travel to the heart after passing through the cardiac plexus, and finally innervate the SA & AV nodes, heart muscle, and coronary arteries.
What is the general effect of sympathetic stimulation of the heart?
Increases heart rate, increase force of contraction, and dilates coronary arteries (via β2-receptors on coronary vessels).
Where do the presynaptic parasympathetic fibers originate and end?
Presynaptic parasympathetic fibers are bundles of axons from the vagus nerve, which originates in the medulla oblongata. These fibers travel through the cardiac plexus to innervate the intrinsic ganglia (postsynaptic cell bodies) of the heart wall, which project the majority of their fibers to the SA and AV nodes.
Where are the postsynaptic fibers located?
Heart wall…mostly wall of right atrium and interatrial septum.
What is the general effect of parasympathetic stimulation of the heart?
Slows heart rate