FOCUS QUESTIONS and ANSWERS:

FOCUS QUESTIONS and ANSWERS:

1. Organize the innervation and blood supply of a complete intercostal space.

Nerves: An intercostal space is typically supplied by an intercostal nerve. Intercostal nerves are continuations of the ventral primary rami of spinal nerves that travel around the trunk in a groove under each rib. Just lateral to the costovertebral joint, the nerves (and arteries and veins) give off collateral branches that then travel on top of each rib. Other important branches of the intercostal nerves include the lateral cutaneous branches, coming off at about the midaxillary line, and the anterior cutaneous branches, emerging just lateral to the sternum.

Blood supply:

The thoracic aorta gives off 9 pairs of posterior intercostal and 1 pair of subcostal arteries. (The first two intercostal spaces are supplied by branches of the costocervical trunk to be studied later.)
The subclavian artery gives off the internal thoracic artery from which arise the anterior intercostal arteries
The axillary arteries give rise to the highest and most lateral thoracic arteries.

Each intercostal space is supplied by three arteries, a large posterior intercostal artery and a small pair of anterior intercostal arteries.

2. Do you find any thymic nodules? What are they?

This is an observation question. Remnants of the thymus, if present, should be in the anterior mediastinum. Although thymic nodules are rare, the remaining fat is in lobes that are shaped like the thymus that used to be there. (Greek, thymus = warty excrescence)

3. Define the boundaries of the superior mediastinum.

Boundary	Structure
Superior	superior thoracic aperture
Inferior	plane defined by sternal angle and T4/T5 IV disc
Lateral	mediastinal pleura
Anterior	manubrium of the sternum
Posterior	spinal column

4. Observe the formation of the superior vena cava (confluence of both brachiocephalic veins), and relate its position to the manubrium and other great vessels.

The superior vena cava lies immediately to the right of the manubrium. It is overlapped on its left margin by the ascending aorta. Posteriorly, it lies against the right pulmonary artery and the right superior pulmonary vein.

5. Are there cardiac nerves arising from the left vagus?

The left vagus normally gives parasympathetic branches to the cardiac plexus. They are most easily seen where the vagus crosses the aortic arch.

6. Do you find a vertebral artery from the arch of the aorta?

Sometimes the left vertebral artery will branch directly from the aortic arch.

7. Is the artery to the atrioventricular node a branch of the right, left, or both coronary arteries?

In 80-85% of people, the artery to the AV node is a branch of the right coronary artery. It arises just before the RCA gives off the posterior interventricular branch.

8. Define anterior cardiac and small cardiac veins.

Anterior cardiac veins: 3 or 4 small vessels arising on the anterior surface of the right ventricle. They cross the RCA (and the coronary sulcus) and end by penetrating the wall of the right atrium. Notably, most other veins drain into the coronary sinus rather than directly into the right atrium.

Small cardiac vein: usually begins as the marginal vein along the heart's acute margin. It receives tributaries from the right atrium and turns to the back of the heart, running with the RCA in the coronary sulcus. It ends by dumping into the right end of the coronary sinus.

9. Review the cardiac plexus and its distribution along the coronary vessels. (Latin, plectere = to braid)

The cardiac plexus is a network of sympathetic and parasympathetic nerve fibers located in the concavity of the arch of the aorta and behind it on the trachial bifurcation (the superficial and deep plexuses respectively). The sympathetic nerves, which increase the rate and force of the heartbeat and dilate the arteries, arise from cervical and thoracic ganglia. The vagus nerve supplies the parasympathetic fibers, which act in opposition to the sympathetics.

10. Define endocardium.

The endocardium is the thin internal layer or lining membrane of the heart. It also covers the heart's valves.

11. Examine the right atrioventricular (tricuspid) valve. Define the cusps.

There are three cusps. The two larger ones are the anterior and the septal cusps. The smaller one is the posterior cusp.

12. Define chamber walls: interventricular (or interatrial), anterior and posterior.

Right atrium: thin-walled sinus venarum posteriorly, more muscular anteriorly (including a muscular auricle), with interatrial septum between it and the left atrium

Left atrium: thin-walled portion posteriorly, muscular auricle more anteriorly, with interatrial septum between it and the right atrium

Right ventricle: lateral and anterior walls are muscular, while the posterior portion is mostly composed of interventricular septum

Left ventricle: interventricular septum is more anterior, rest of wall is muscular

13. In the right ventricle, define papillary muscles, chordae tendineae, and tricuspid valve cusps. (Latin, papilla = nipple)

The right ventricle usually has only two papillary muscles (anterior and posterior); occasionally there is one or more small septal papillary muscles. They are muscular projections from the ventricular wall which have tendinous cords (chordae tendineae) extending to the tricuspid valve cusps. The anterior muscle is the largest and has tendinous cords attaching to the anterior and posterior cusps. The smaller posterior muscle, which may consist of several parts, has cords attaching to the posterior and septal cusps. The septal muscle, when there is one, has cords attaching to the anterior and septal cusps. If there is no septal muscle, chordae tendineae arise directly from ventricle's septal wall.

14. Do you find a septomarginal trabecula?

The septomarginal trabecula (moderator band), when present, is a muscular ridge of myocardium extending from the right ventricle's septal wall to the base of the anterior papillary muscle. (Latin, trabecula = little beam)

15. Name the semilunar cusps of the pulmonary valve.

The pulmonary valve's three semilunar cusps are named according to their orientations: right, left and anterior.

16. Does the left atrioventricular (mitral, bicuspid) valve have any commissural cusps? Note relation of anterior cusp to aortic wall.

Commissural cusps are small accessory cusps occurring between the named cusps (anterior and posterior). The anterior cusp of the mitral valve abuts and curves around the base of the aorta.

17. What is the aortic vestibule?

The aortic vestibule is the superior portion of the left ventricle which leads into the root of the aorta.

18. Name the semilunar cusps of the aortic valve.

The aortic valve's three cusps, like the pulmonary valve's, are named according to position: right, left and posterior. The right and left cusps are associated with the right and left coronary arteries. The posterior cusp is referred to as the "non-coronary cusp".

19. Where are the sounds associated with each heart valve best heard with a stethoscope?

Mitral: 5th left intercostal space
Tricuspid: 4th left intercostal space
Pulmonary: left upper sternal border
Aortic: right upper sternal border

20. What are the fibrous rings (annulus fibrosus)?

There are four fibrous rings, one surrounding each valve. They are made of dense collagen and are part of the heart's fibrous skeleton. This skeleton is the point of attachment/insertion for cardiac muscle - the atrial muscle from above and the ventricular muscle from below.

21. What is the relationship of the heart's fibrous skeleton to its conduction system? Why is this important?

The fibrous skeleton provides attachment for heart's myocardium and valves. Additionally, it serves as an electrical insulator between the atria and ventricles penetrated only by the conduction system. This ensures that there is a pause between the contraction of the atria (leading to ventricular filling) and the contraction of the ventricles (ventricular ejection or emptying).