Thorax and Ribs Anatomy Quiz

Thorax

• Area between the head and abdomen
• Contains the heart, lungs, and blood vessels
• Surrounded by the thoracic cage, formed of:
  • 12 ribs
  • Sternum
  • Thoracic vertebrae
  • Clavicle
  • Intercostal muscles

Ribs

• Set of 12 ribs
• Articulate posteriorly with the vertebral column (T1-T12)
• Terminate anteriorly with cartilage called costal cartilage
• Types of ribs:
  • True ribs (vertebrosternal): attached to sternum (ribs 1-7)
  • False ribs: don't connect directly to sternum (ribs 8-12)
    • First 3 pairs (ribs 8-10) are called vertebrochondral as they connect to the sternum through the costal cartilage of the rib above
    • Last 2 pairs (ribs 11-12) are floating ribs as they connect to the vertebrae alone
• Space between ribs is called the intercostal space and contains:
  • Intercostal muscles
  • Neuromuscular bundles
  • Intercostal nerves, veins, arteries
• Superficial surface of the rib cage is covered with thoracolumbar fascia and provides attachment to neck, pectorals, back, and abdominal muscles
• Each rib consists of:
  • Head: articulates with the thoracic vertebrae through the superior costal facet of the same vertebra, inferior costal facet of the upper vertebra, and transverse costal facet of the same vertebra
  • Neck: extends 3 cm laterally from the head and has two surfaces:
    • Anterior soft surface
    • Posterior rough surface for attachment of the costotransverse ligament
  • Shaft: contains the angle of the rib and extends downward and laterally

Sternum

• Flat vertical bone at the center of the chest
• Protects the heart and muscles
• Connects the ribs through costal cartilage to form the anterior rib cage
• Divided into:
  • Manubrium: superior segment
  • Body: middle portion
  • Xiphoid process: narrow distal segment

Sternum Deformities

• Pectus excavatum (funnel chest):
  • More common
  • Sternum depressed posteriorly leading to depression of adjacent costal cartilage inward and depression of the anterior chest wall
• Pectus carinatum:
  • Outward displacement of the sternum and costal cartilage leading to abnormal protrusion of the anterior chest wall

Diaphragm

• Muscle separating the thoracic cavity from the abdominal cavity
• Relaxed: dome shape (during expiration)
• Contracted: flattened to increase the volume in the thoracic cavity (during inspiration)
• Structure:
  • Upward, curved, c-shape structure of muscle and fibrous tissue
  • Separates thoracic cavity from abdominal cavity
  • Formed of:
    • Central tendon forming the crest of the dome
    • Peripheral fibers
• Contains several openings:
  • Caval opening in the central tendon containing the inferior vena cava
  • Esophageal hiatus containing the esophagus in the posterior part of the diaphragm
  • Aortic hiatus containing the aorta and thoracic duct in the posterior part of the diaphragm
• Nerve supply:
  • Central part: phrenic nerve (C3-C5)
  • Peripheral part: intercostal nerves (T5-T11), subcostal nerve (T12)

Diaphragm Function

• Main muscle of respiration
• During inhalation:
  • Diaphragm contracts and moves inferiorly, increasing volume in the thoracic cavity, decreasing intrathoracic pressure, and allowing air to move in (with help of external intercostal muscles)
• During exhalation:
  • Diaphragm relaxes, allowing air to move out by the elastic recoil of the diaphragm, with assist from internal intercostal muscles and abdominal muscles during forced expiration

Diaphragmatic Dysfunction

• Functional disorders: lead to decreased muscle function, ranging from muscle fatigue or weakness to complete paralysis (as seen in COPD, mechanical ventilation patients, or myopathies)
• Anatomical disorders: characterized by normal diaphragm function, but limited movement due to structural and anatomical derangement (these disorders include herniation of the diaphragm and diseases of the other related organs obstructing its movement)

Intercostal Muscles

• Function:
  • Helps move the chest wall
  • Involved in the mechanical aspect of breathing
  • Helps expand and shrink the size of the chest cavity
• Nerve supply: intercostal nerves, mainly ventral rami of thoracic spinal nerves
• Supplied by intercostal arteries and drained by intercostal veins
• Layering:
  • External intercostal muscles:
    • Function: quiet and forced inhalation
    • Origin: ribs 1-11
    • Insertion: ribs 2-12
    • Direction: downward, forward, medially
  • Internal intercostal muscles:
    • Function: forced expiration
    • Origin: ribs 2-12
    • Insertion: ribs 1-11
    • Direction: upward, forward, laterally
  • Innermost intercostal muscles:
    • Deep layer of intercostal muscles