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Anatomy 2- Thoracic Wall
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The thorax is described as the upper part of the trunk—the part of the body between the neck and the
abdomen
• The word chest is often used as a synonym for thorax in roughly two senses
• In the anatomical sense, chest is a synonym for thorax
• In the colloquial sense, chest tends to refer to the anterior wall of the thorax
• Fundamentally, there are two components that make up the thorax
• The musculoskeletal thoracic wall
• The viscera-containing thoracic cavity
Thorax Shape
• The skeletal components of the thoracic wall—mainly the ribs—lend a conical shape to the thorax
• The dome-shaped respiratory diaphragm protrudes superiorly into the thoracic cavity, which has two effects
– The thoracic cavity is smaller than might be expected from the external appearance of the thorax
– The inferior aspect of the thoracic cavity has an irregular concavity
• The thorax is cone-shaped
• The diaphragm is dome-shaped
Contents of Thorax
• The thoracic cavity contains the primary organs of the respiratory and cardiovascular systems
– Lungs, heart
• As well, the thoracic cavity contains key components of other major systems
– Esophagus, thoracic duct, thymus
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Thoracic Wall
The thoracic wall consists of two main components
– Skeleton
– Muscle
As well, the wall contains skin, subcutaneous tissue and fascia
All of the above structures—where covering the posterior aspect of the thorax—constitute the back
Skin—subcutaneuos tissue—oblique muscle—intercostal muscle—endothoracic fascia—parietal pleura—
visceral pleura—lung/cavity
Skeleton of the Thorax
• The skeleton of the thorax (thoracic cage, or ribcage) consists of the twelve ribs, the sternum, and the thoracic
vertebrae
• The bones are united by joints and cartilage to form a cylinder
• The domed, birdcage shape of the thoracic cage provides strength
• Necessary for protection of vital contents
• The thoracic cage extends inferiorly to protect abdominal contents
Openings
• The skeleton of the thorax has two openings
– It has a narrow opening superiorly
• Thoracic inlet:(superior thoracic aperture) allows communication with the neck and upper limbs
• The inlet is relatively narrow, and has an oblique orientation, sloping downward
anteriorly
• The inlet is bordered anteriorly by the manubrium, laterally by the first ribs, and
posteriorly by the first thoracic vertebra
– It has large opening inferiorly
• Thoracic outlet: (inferior thoracic aperture) is spacious compared to the inlet
• It is closed by the diaphragm and thus not continuous per se with the abdomen
• The outlet is bordered anteriorly by the xyphoid process, laterally by the ribs, and
posteriorly by the 12th thoracic vertebra
Anatomy 2- Thoracic Wall
Joints of Thorax
• The individual joints of the thoracic skeleton have a relatively small range of motion
• However, the overall movement of the thoracic wall is crucial for proper lung ventilation
• Many joints—mainly synovial—contribute directly to movement of the thoracic wall
• Costovertebral, interchondral, sternocostal, sternoclavicular, and manubriosternal
• Of these, the costovertebral joints—consisting of joints of the heads of the ribs, and costotransverse joints—are
the most significant
Costovertebral Joints
• The heads of the ribs articulate with the costal facets of the vertebral bodies
• The head is connected very tightly to the facets by two ligaments
– Radiate and intra-articular
• For ribs 2-9, the intra-articular ligament bisects the joint cavity creating a double-synovial cavity
– Permits slight, but complex movements
Costotransverse Joints
• The tubercle of the rib articulates with the facets of the transverse processes
• Strong costotransverse ligaments bind these joints and limit their movements to slight gliding
Upper Rib movement
• The articular surfaces of the tubercles of ribs 1-6 are convex and fit into concavities on the transverse processes
– Movement at the costotransverse joints is thus rotation of the ribs about a somewhat transverse axis
– Movement at the joints of the head of the rib is a slight pivot
• The sternal ends of the upper ribs are elevated and depressed in the sagittal plane
– Pump-handle movement of upper ribs
• Elevation of the upper ribs results in greater A-P diameter of the ribcage
– Depression of the upper ribs results in lesser A-P diameter
Anatomy 2- Thoracic Wall
Lower Rib Movement
• The articulating surfaces of the costotransverse joints of ribs 7-10 are flat
– Movement at the costotranverse joints of the lower ribs is thus a true gliding action
– As a consequence, movement at the joints of the head of the rib is also a slight gliding
• The previously described joint movements result in elevation-depression of the lateral-most portions of the
lower ribs
– Bucket-handle movement of ribs
• Elevation of the lateral part of the lower ribs results in greater transverse diameter of the ribcage
Muscles of the Thorax
• The skeletal framework of the thoracic wall provides extensive attachment sites for muscles associated with
many other body regions
– Neck, abdomen, back, upper limb
Intrinsic Muscles
• There are several intrinsic, or true muscles of the thoracic wall
– Serratus posterior*
– Levatores costarum *
– Intercostals**
– Subcostals**
– Tranversus thoracis **
*Generally studied with the back
**Innervated by intercostals nerves
• All of the intrinsic muscles have some degree of activity in pulmonary ventilation (breathing)
– This occurs via elevation and depression of the ribs
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All intercostal muscles stiffen the intercostal space
– Prevents outward bulging on inward suction of the spaces during breathing
The intercostal muscles occupy the intercostal spaces
There are three groups of intercostal muscle
– 1. External
• The 11 pairs of extend from the tubercles of the ribs to the costochondral junctions
• Anteriorly the muscle is replaced by the external intercostal membrane
• The muscle fibers run inferoanteriorly from the rib above to the rib below
– 2. Internal
• The 11 pairs of internal intercostal muscles extend from the angles of the ribs to the sternum
• Posteriorly the muscle is replaced by the internal intercostal membrane
• The muscles run inferoposteriorly from the rib above to the rib below
• Run at right angle to external intercostals
– 3. Innermost
• The innermost intercostals are essentially the deeper part of the internal intercostals
• They are separated from the internal intercostals by neurovasculature
• They are most concentrated in the lateral parts of the intercostal spaces
The subcostal muscles are found on the internal surface of the ribs
– They are well developed in the lower thoracic wall
The subcostals blend in with the innermost intercostals and have the same fiber orientation
Subcostals extend from one rib to the second or third below
Transversus thoracis consists of 4-5 slips of muscle on the deep surface of the thoracic wall
The slips radiate outwardly from the posteroinferior aspect of the sternum
– Insert on internal surface of costal cartilage
Transversus thoracis may have a weak expiratory function, or may be involved in proprioception
Anatomy 2- Thoracic Wall
Neurovasculature of the Thoracic Wall
• Much of the neurovasculature of the thoracic wall travels in the intercostal spaces
• Intercostal veins, arteries, and nerves are generally located in the costal groove, in between the internal and
innermost intercostals
– The veins are most superior, the arteries in the middle, and the nerves most inferior
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The intercostal neurovasculature features collateral
branches
These branches arise near the angles of the ribs and travel
on the superior surface of the inferior rib
A chest tube may be inserted into the thorax
• Usually to remove air or fluid
Insertion is generally in the mid-axillary line at the 7th or 8th
intercostal space
• Tube must be introduced along upper margin of rib
to protect VAN
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The twelve pairs of thoracic spinal nerves supply the thoracic wall
• The anterior rami of T1-T11 form intercostal nerves, while the anterior ramus of T12 is known as the
subcostal nerve
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Most intercostal nerves give rise to multiple branches
– Muscular: Supply intercostal muscles
– Lateral cutaneous: Arise near mid-axillary line
– Anterior cutaneous: Arise parasternally
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The arterial supply to the thoracic wall derives from two main sources
– Thoracic aorta
• Gives rise to posterior intercostal arteries
– Subclavian artery
• Gives rise to internal thoracic arteries, which in turn give rise to anterior intercostal arteries
Anatomy 2- Thoracic Wall
Diaphragm
• The diaphragm is a musculotendinous partition separating thoracic and abdominal cavities
• It is the chief muscle of breathing
Shape
• Viewed anteriorly, or posteriorly, the diaphragm is double-domed
– Convexity faces thorax
• Normally the right dome is higher than the left dome (Liver )
Parts
• There are two basic parts of the diaphragm
– Muscular part--Situated peripherally
– Aponeurotic part (central tendon)--Located centrally
• It is the muscular part of the diaphragm that forms attachments
– When the diaphragm contracts it descends, the central tendon moving toward the attachments
Musculature
• For descriptive purposes the muscle of the diaphragm is divided into three parts, based on attachments
– Sternal part-- Attaches to posterior xiphoid process
– Costal part-- Attaches to internal surfaces of inferior six costal cartilages and ribs
– Lumbar part-- Attaches to upper three lumbar vertebrae; twelfth rib
Innervation
• All motor innervation to the diaphragm is from the phrenic nerves (C3-C5)
• Sensory innervation of the diaphragm (pain and proprioception) is from two sources
– Phrenic nerves
• Most of diaphragm
– Intercostal (T5-T11) and subcostal (T12) nerves
• Peripheral parts of diaphragm
Arterial Supply
• The arteries of the diaphragm form a branch-like pattern on both inferior and superior surfaces
• The superior surface of the diaphragm receives its blood supply from two main sources
• Branches of internal thoracic arteries
• Pericardiophrenic and musculophrenic arteries
• Branches of thoracic aorta
• Superior phrenic arteries
• The inferior surface of the diaphragm receives its
blood supply from the first branches of the abdominal aorta
• Inferior phrenic arteries
Anatomy 2- Thoracic Wall
Thoracic Cavity
The thoracic cavity is divided into three compartments
1. Left pleural cavity
2. Right pleural cavity
3. Mediastinum
• Heart, great vessels
Neck Relation
• The superior thoracic aperture opens directly into the root of the neck
– The apices of the lungs extend into the neck
• Major visceral structures pass between the neck and thorax
– Trachea and esophagus in the midline
– Neurovasculature laterally
Upper Limb Relation
• The axillary inlet, or gateway to the upper limb, lies on either side of the superior thoracic aperture
• The axillary inlets are formed by the scapulae posteriorly, the clavicles anteriorly, and the first ribs medially
– The subclavian vessels pass over the first rib
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Abdomen Relation
• The diaphragm separates the thorax from the abdomen
• Structures pass from thorax to abdomen in two general ways
– Pierce the diaphragm
• Inferior vena cava, esophagus
– Pass posteriorly to the diaphragm
• Aorta, muscle