GEN ANATOMY

• Thorax


  Region of the body between the neck and the abdomen, flattened in front and behind but rounded at the sides
• Thoracic cage


  • Framework of the walls of the thorax, formed by the vertebral column behind, the ribs and intercostal spaces on either side, and the sternum and costal cartilages in front
• Mediastinum


  Median partition of the thoracic cavity
• Pleura


  Thin membrane covering the lungs, visceral pleura passes from each lung at its root to the inner surface of the chest wall where it is called the parietal pleura
• Pleural cavities


  Membranous sacs formed between the lungs and the thoracic walls
• Thoracic wall


  • Covered on the outside by skin and muscles, lined with parietal pleura
  • Formed posteriorly by the thoracic part of the vertebral column, anteriorly by the sternum and costal cartilages, laterally by the ribs and intercostal spaces, superiorly by the suprapleural membrane, and inferiorly by the diaphragm
• Sternum


  Flat bone in the midline of the anterior chest wall, divided into manubrium, body, and xiphoid process
• Manubrium


  • Upper part of the sternum, articulates with the body of the sternum, clavicles, and upper costal cartilages
• Body of sternum


  • Articulates above with the manubrium and below with the xiphoid process, articulates with 2nd to 7th costal cartilages
• Xiphoid process


  • Thin plate of cartilage at the lower end of the sternum, becomes ossified in adulthood, no ribs or costal cartilages attached
• Sternal angle


  Angle formed by the articulation of the manubrium and body of the sternum, marked by a transverse ridge at the level of the 2nd costal cartilage
• Sternum is a common site for marrow biopsy due to the presence of red hematopoietic marrow, and may be split at surgery to access the heart, great vessels, and thymus
• Categories of ribs


  • True ribs (upper 7 pairs attached to sternum)
  • False ribs (8th-10th pairs attached to each other and 7th rib)
  • Floating ribs (11th and 12th pairs with no anterior attachment)
• Typical rib


  • Long, twisted, flat bone with rounded superior border and sharp inferior border, costal groove accommodates intercostal vessels and nerve, has head, neck, tubercle, shaft, and angle
• First rib


  • Small, flattened from above downward, with scalenus anterior muscle attached, subclavian artery and vein and lower trunk of brachial plexus cross over it
• Costal cartilages


  Bars of cartilage connecting ribs to sternum, contribute to elasticity and mobility of thoracic wall
• Joints of the sternum

  • Manubriosternal joint (cartilaginous, allows some angular movement)
  • Xiphisternal joint (cartilaginous, xiphoid process fuses with body of sternum in middle age)
• Joints of the ribs

  • Synovial joints between rib heads and vertebral bodies, and between rib tubercles and transverse processes
  • Cartilaginous joints between ribs and costal cartilages
• Joints of the costal cartilages

  • 1st cartilages articulate with manubrium by cartilaginous joints
  • 2nd-7th cartilages articulate with sternum by synovial joints
  • 6th-10th cartilages articulate with each other by small synovial joints
  • 11th and 12th cartilages embedded in abdominal musculature
• Movements of ribs and costal cartilages

  1. 1st ribs and cartilages are fixed and immobile

  2. Raising and lowering of other ribs involves rotation of rib necks around their own axes
• Thoracic outlet


  Opening at the root of the neck through which important vessels and nerves pass, bounded by 1st thoracic vertebra, 1st ribs, and manubrium
• Thoracic inlet


  Large opening at the base of the thorax through which the esophagus, vessels, and nerves pass, bounded by 12th thoracic vertebra, costal margin, and xiphisternal joint
• Thoracic outlet syndrome is caused by compression of the brachial plexus and subclavian vessels between the bones at the thoracic outlet
• Intercostal spaces


  • Contain external, internal, and innermost intercostal muscles, with intercostal nerves and vessels running between the intermediate and deepest muscle layers
• External intercostal muscles


  • Most superficial layer, fibers directed downward and forward
• Internal intercostal muscles


  • Intermediate layer, fibers directed downward and backward
• Innermost intercostal muscles


  • Deepest layer, lined internally by endothoracic fascia and parietal pleura
• Intercostal nerves and blood vessels

  Arranged in the order: intercostal vein, intercostal artery, intercostal nerve (VAN)
• Intercostal muscles


  1. External intercostal muscle: fibers directed downward and forward

  2. Internal intercostal muscle: fibers directed downward and backward

  3. Innermost intercostal muscle: incomplete muscle layer, crosses more than one intercostal space
• Intercostal muscles


  • When they contract, they pull the ribs nearer to one another
  • Tone of the muscles during respiration strengthens the tissues of the intercostal spaces
• Intercostal muscles are supplied by the corresponding intercostal nerves
• Posterior intercostal arteries


  First two spaces are branches from the superior intercostal artery, lower nine spaces are branches of the descending thoracic aorta
• Anterior intercostal arteries


  First six spaces are branches of the internal thoracic artery, lower spaces are branches of the musculophrenic artery
• Intercostal veins


  Posterior intercostal veins drain into the azygos or hemiazygos veins, anterior intercostal veins drain into the internal thoracic and musculophrenic veins
• Intercostal nerves


  Anterior rami of the first 11 thoracic spinal nerves, 12th thoracic nerve is the subcostal nerve
• Intercostal nerve distribution


  1. Enters intercostal space between parietal pleura and posterior intercostal membrane, runs forward inferiorly to the intercostal vessels

  2. First 6 nerves distributed within their intercostal spaces, 7th-9th pass deep to costal cartilages into abdominal wall, 10th-11th pass directly into abdominal wall
• Intercostal nerve branches


  • Rami communicantes
  • Collateral branch
  • Lateral cutaneous branch
  • Anterior cutaneous branch
  • Muscular branches
  • Pleural sensory branches
  • Peritoneal sensory branches
• First intercostal nerve


  Joined to brachial plexus by a large branch, remainder of nerve is small with no anterior cutaneous branch
• Second intercostal nerve


  Joined to medial cutaneous nerve of arm by intercostobrachial nerve
• • Exceptions noted, 1st-6th intercostal nerves supply skin, parietal pleura, and intercostal muscles
  • 7th-11th intercostal nerves also supply skin and parietal peritoneum of abdominal wall