Mediastinum

1. Relationships of the heart to other structures in mediastinum
   1. Thorax is divided into the superior mediastinum and inferior mediastinum.
   2.  Inferior mediastinum:

      i.      Anterior mediastinum: extends from posterior surface of sternum to anterior surface of pericardial sac

1. Fat
2. Thymus gland (infants)
3. Lymph nodes

   ii.      Middle mediastinum

1. HEART
2. Pericardium
3. Main bronchi
4. Great vessels
5. Phrenic nerves

   iii.      Posterior mediastinum: Located posterior to the pericardial sac and diaphragm and anterior to vertebral bodies T5-T12

1. Thoracic aorta
2. Esophagus
3. Azygous venous system
4. Thoracic duct
5. Vagus nerves
6. Splanchic nerves

Coronary Arteries

RIGHT CORONARY- (from the ascending aorta)

Branches:

• R atrial branch (gives off the SA nodal branch)
• Conal branch
• R marginal branch (w/ small cardiac vein)
• Posterior interventricular artery (PAD) – accompanies middle cardiac vein

LEFT CORONARY- (from ascending aorta)

Branches:

• Circumflex (gives off L marginal artery)
• Anterior interventricular artery (LAD) – may give rise to 1-2 diagonal branches across anterior surface of LV. Accompanies the great cardiac vein.

ANASTOMOSES

nodal anastomoses

conus arteriosum

circumflex

anterior interventricular septum

posterior interventricular septum

Venous Drainage of Thoracic Wall

The anterior aspect of the thorax is drained by the internal thoracic vein into the brachiocephalic vein.

The posterior aspect is drained by the axygos system into the SVC.

• The 1st intercostal space is drained by the highest intercostal vein into the brachiocephalic
• The rest of the right side is drained by the azygos system into the SVC
• 2-4 of the left side is drained by the accessory hemiazygous vein
• 5-12 of the left side is drained by the hemiazygous vein

Arteries of the Thoracic Wall

The anterior aspect of the thoracic wall is supplied by the internal thoracic artery.

The posterior aspect is supplied by:

ICS 1: posterior IC artery or highest IC artery (costocervical trunk of the subclavian)

ICS 2-11 : posterior intercostal arteries (thoracic aorta)

ICS 12: subcostal artery (thoracic aorta)

Diaphragm Openings

Aortic opening (T12) : greater splanchic n (T5-T9), azygos vein, thoracic aorta, thoracic duct

Esophageal opening (T10) : R&L vagus branches, esophagus, esophageal branch of L gastric A&V

Caval opening ( T8): phrenic nerves (C3-C5), IVC, lymphatics

Splanchic Nerves

The splanchic nerves are paired nerves that carry fibers of the autonomic nervous system to the viscera. All of them carry sympathetic fibers except the pelvic splanchic nerves, which carry parasympathetic.

Nerve-origin-target

thoracic splanchic:

• greater splanchic n- t5-t9 – celiac ganglia
• lesser splanchic n- t10-t11 – superior mesenteric ganglia
• least splanchic n- t12 – kidney

lumbar splanchic n- L1-L2- inferior mesentery, intermesenteric, hypogastric

sacral splanchic n- sacral part of sympathetic trunk- inferior hypogastric, pelvic viscera

pelvic splanchic n- s2-s4- sigmoid colon, rectum, inferior hypogastric, pelvic viscera

Rib Moving Muscles

Rib raisers:

• serratus posterior superior
• levator costarum
• external IC
• innermost IC

Rib depressers:

• serratus posterior inferior
• internal IC
• subcostal
• transverus thoracis

Serratus Posterior Muscles

The serratus posterior superior m attaches the nuchal ligament and the spinous processes of c7-t3 to the superior borders of ribs 2-4. Innervated by 2-5 IC nerves. Elevates ribs.

The serratus posterior inferior m ataches the spinous processes of t11-L2 to ribs 8-12. Innervated by anterior rami of T9-12 thoracic nerves. Depresses ribs.

Intercostal Muscles

This is the group of muscles between each rib. The group (from posterior to anterior) consists of: innermost m, internal m and external m. All 3 muscles are innervated by the intercostal nerve. The intercostal vascular bundle travels between the innermost and internal mm.

1. external IC m- elevates ribs during forced inspiration
2. internal IC m- depresses ribs during forced respiration
3. innermost IC m- elevates ribs during forced respiration

Transversus Thoracis Muscle

This muscle is a weak depresser of the ribs. It attaches the posterior lower sternum to the internal surface of costal cartilages 2-6.

It is innervated by the intercostal nerve.