Thorax

• Thorax


  The upper part of the trunk
• Contents of the thorax

  • Thoracic cage
  • Thoracic cavity
  • Muscles of thorax
  • Movement of the thoracic cage
  • Viscerals of thorax
  • The Heart
• Thoracic cage


  • Bony skeleton of the thorax
  • Dome-shaped structure made up of sternum, ribs, and thoracic vertebrae
  • Protects vital organs
  • Plays a major role in inspiration and expiration
  • Provides attachment for and supports the weight of the upper limbs
  • Provides attachment for many muscles
• Sternum


  • Flat, elongated bone that forms the middle of the anterior part of the thoracic cage
  • Consists of manubrium, body, and xiphoid process
  • Protects the mediastinal viscera
• Types of ribs


  • True ribs (1st-7th ribs)
  • False ribs (8th-10th ribs)
  • Floating ribs (11th-12th)
• Ribs


  • Curved, flat bones that form most of the thoracic cage
  • Have a head, neck, tubercle, body, and costal groove
  • 1st rib has upper and lower surface, internal and external borders, and a scalene tubercle
  • 2nd rib has a small tubercle and non-articular facet
  • 10th-12th ribs have only 1 articular facet on the head, no neck, no tubercle
• Costal cartilages


  • Connect the terminal end of the ribs to the sternum or upper cartilages
  • Increase in length from 1st to 7th
  • Increase in obliquity from 5th to 10th
• Thoracic joints


  • Costochondral
  • Interchondral
  • Sternocostal
  • Sternoclavicular
  • Manubriosternal
  • Xiphisternal
  • Intervertebral
  • Costovertebral
  • Costotransverse
• Thoracic vertebrae


  • Typical (T2-T9) and atypical (T1, T10-T12)
  • Have a body, vertebral arches, and processes for muscular attachment and bone articulation
• Subdivisions of the mediastinum

  • Superior mediastinum
  • Anterior mediastinum
  • Middle mediastinum
  • Posterior mediastinum
• Superior mediastinum


  • Bounded above by the thoracic inlet, below by the sternal angle and T4-T5 intervertebral disc
  • Bounded anteriorly by the manubrium sterni, posteriorly by T1-T4 vertebrae
  • Contains sternothyroids, sternohyoids, longus colli, superior sternopericardial ligaments, remnant of the thymus, lymph nodes, large arteries and veins, nerves, trachea, esophagus, thoracic duct
• Anterior mediastinum


  • Smallest of the three subdivisions of the inferior mediastinum
  • Bounded anteriorly by the sternal body, posteriorly by the fibrous pericardium
  • Contains lymph nodes, mediastinal branches of internal thoracic arteries, loose connective tissue, inferior sternopericardial ligament
• Middle mediastinum


  • Largest part of the inferior mediastinum
  • Bounded anteriorly and posteriorly by the fibrous pericardium, laterally by the mediastinal pleura
  • Contains the heart, ascending aorta, pulmonary trunk and arteries, lower half of SVC, pulmonary veins, inferior vena cava, bifurcation of trachea and main bronchi, phrenic nerves, deep cardiac plexus, some tracheobronchial lymph nodes
• Posterior mediastinum


  • Anteriorly bounded by bifurcation of trachea, pulmonary vessels, fibrous pericardium, posterior diaphragm
  • Posteriorly bounded by T5-T12 vertebrae, mediastinal pleura
  • Contains descending thoracic aorta and branches, azygos and hemiazygos veins, vagus and lower thoracic splanchnic nerves, esophagus, thoracic duct, posterior mediastinal lymph nodes
• Thoracic apertures


  Openings that allow passage of structures, communication between thorax and other body parts
• Thoracic apertures


  • Superior thoracic aperture
  • Inferior thoracic aperture
• Muscles of the thorax

  • Serratus posterior superior
  • Serratus posterior inferior
• Serratus posterior superior


  Originates from nuchal ligament and T1-T3 spinous processes, inserts on superior borders of 2nd-4th ribs, innervated by 2nd-5th intercostal nerves, elevates ribs
• Serratus posterior inferior


  Originates from T9-T12 spinous processes, inserts on inferior borders of 8th-12th ribs, innervated by anterior rami of T9-T12 spinal nerves, depresses ribs
• Chest radiographs can show deviation of the mediastinum, enlargement due to malignant tumors or bleeding, and widening due to heart enlargement
• The mediastinum can be examined and biopsied during mediastinoscopy
• Anteroposterior (AP) and lateral chest radiograph


  Deviation of the mediastinum towards the unaffected pleural cavity
• Enlargement of the mediastinum

  Due to malignant tumor of the mediastinal lymph nodes
• Enlargement of the mediastinum

  Bleeding from the large vessels of the mediastinum can also result in its enlargement
• Widening of inferior mediastinum


  Due to enlargement of the heart
• Mediastinoscopy


  Using a mediastinoscope to examine the mediastinum and take biopsies of its lymph nodes
• Thoracic apertures


  Openings that allow the passage of structures and communication between the thorax and other parts of the body
• Thoracic apertures


  • Superior thoracic aperture
  • Inferior thoracic aperture
• Serratus Posterior Superior


  Originates from nuchal ligament, spinous processes of C7 to T3 vertebrae and inserts on superior borders of 2nd to 4th ribs, innervated by 2nd to 5th intercostal nerves, elevates ribs
• Serratus Posterior Inferior


  Originates from spinous processes of T11 to L2 vertebrae and inserts on inferior borders of 8th to 12th ribs near their angles, innervated by anterior rami to T9 to T12 spinal nerves, depresses ribs
• Levator costarum


  Originates from transverse processes of T7-11 and inserts on subjacent ribs between tubercle and angle, innervated by posterior primary rami of C8-T11 nerves, elevates ribs
• Diaphragm


  • Dome-shaped, musculotendinous partition between the thoracic and abdominal cavities, has concave inferior and convex superior surface, divided into sternal, costal and lumbar parts based on peripheral attachment
• Diaphragm attachments


  Peripheral: xiphoid process, 6th cartilage, arcuate ligament, left and crura. Central: pericardiacophrenic ligaments attaching it to pericardium
• Diaphragm openings


  Aortic hiatus, Oesophageal hiatus, Vena caval foramen
• Innervation of the Diaphragm

  • Motor fibres: Phrenic nerve (C3–C5)
  • Sensory fibres (central part): Phrenic nerve (C3–C5)
  • Sensory fibres (peripheral part): Lower intercostal (T5–T11) and subcostal (T12) nerves
• Arterial Supply of the Diaphragm

  • Superior phrenic arteries (from the thoracic aorta)
  • Musculophrenic and pericardiacophrenic arteries (from internal thoracic arteries)
  • Inferior phrenic arteries (from abdominal aorta)
• Venous Drainage of the Diaphragm

  • Musculophrenic veins (tributaries of internal thoracic veins)
  • Pericardiacophrenic veins (tributaries of internal thoracic veins)
  • Superior phrenic vein (right side only) (tributary in inferior vena cava [IVC])
  • Inferior phrenic veins (right vein drains into IVC, left one drains into IVC and left suprarenal vein)
• Lymphatic Drainage of the Diaphragm

  Diaphragmatic nodes, from which lymph drains into phrenic, parasternal and posterior mediastinal nodes. Upper lumbar nodes also receive lymph from the diaphragm.
• Paralysis of a hemidiaphragm

  Occurs following injury to the phrenic nerve of that side
• Accessory phrenic nerve


  Present in certain subjects, so injury to the main phrenic nerve does not result in paralysis of a hemidiaphragm