Thoracic Wall Muscles and Layers PDF

The Thoracic wall Muscles and Layers DR. MARIE P. AFFANA, M.D ALL SAINTS UNIVERSITY SCHOOL OF MEDICINE INTRO TO ANATOMY II PREMED 2 Structure of the Thoracic Wall  Outside  skin and by muscles...

The Thoracic wall Muscles and Layers DR. MARIE P. AFFANA, M.D ALL SAINTS UNIVERSITY SCHOOL OF MEDICINE INTRO TO ANATOMY II PREMED 2 Structure of the Thoracic Wall  Outside  skin and by muscles attaching the shoulder girdle to the trunk.  Inside  lined with parietal pleura.  Framework  Posteriorly :the thoracic part of the vertebral column Anteriorly : the sternum and costal cartilages Laterally : the ribs and intercostal spaces Superiorly : the suprapleural membrane Inferiorly : the diaphragm Muscles of the Thoracic Cage  There are five muscles that make up the thoracic cage;  The intercostals (external, internal and innermost)  The Subcostals,  Transversus thoracis.  These muscles act to change the volume of the thoracic cavity during respiration.  There are some other muscles that do not comprise the thoracic wall, but do attach to it. These include the pectoralis major, minor, serratus anterior and the scalene muscles. The intercostals  The intercostal muscles lie in the intercostal spaces between ribs. They are organised into three layers. External Internal Innermost External Intercostals  There are 11 pairs of external intercostal muscles. They run inferoanteriorly from the rib above to the rib below, and are continuous with the external oblique of the abdomen.  Attachments: Originate at the lower border of the rib, inserting into the superior border of the rib below.  Actions: Elevates the ribs, increasing the thoracic volume.  Innervation: Intercostal nerves (T1-T11). External Intercostal Muscle External Intercostal Muscle Internal Intercostals  These flat muscles lie deep to the external intercostals. Like the external intercostals, they run from the rib above to the one below, but in an opposite direction (inferoposteriorly). They are continuous with the internal oblique muscle of the abdominal wall.  Attachments: Originate at the lower border of the rib, inserting into the superior border of the rib below.  Actions: The interosseous part reduces the thoracic volume by depressing the ribcage, and the interchondral part elevates the ribs.  Innervation: Intercostal nerves (T1-T11). Internal Intercostal Muscle Innermost Intercostals  These muscles are the deepest of the intercostal muscles, and are similar in structure to the internal intercostals.  They are separated from the internal intercostals by the intercostal neurovascular bundle and are found in the most lateral portion of the intercostal spaces.  Attachments: Originate at the lower border of the rib, inserting into the superior border of the rib below.  Actions: The interosseous part reduces the thoracic volume by depressing the ribcage, and the interchondral part elevates the ribs.  Innervation: Intercostal nerves (T1-T11) Innermost Intercostal Muscle Transversus Thoracic  These muscles of the thoracic cage are continuous with transversus abdominis inferiorly.  Attachments: From the posterior surface of the inferior sternum to the internal surface of costal cartilages 2-6.  Actions: Weakly depress the ribs.  Innervation: Intercostal nerves (T1-T11). Transversus Thoracic Subcostals  The subcostal muscles are found in the inferior portion of the thoracic wall. They comprise of thin slips of muscle, which run from the internal surface of one rib, to second and third ribs below. The direction of the fibres parallels that of the innermost intercostal.  Attachments: These originate from the inferior surface of the lower ribs, near the angle of the rib. They then attach to the superior border of the rib 2 or 3 below.  Actions: Share the action of the internal intercostals  Innervation: Intercostal nerves Diaphragm The Diaphragm  Thediaphragm is a double-domed sheet of skeletal muscle, located at the inferior-most aspect of the rib cage. It serves two main functions:  Separates the thoracic cavity from the abdominal cavity (the word diaphragm is derived from the Greek ‘diáphragma’, meaning partition).  Undergoes contraction and relaxation, altering the volume of the thoracic cavity and the lungs, producing inspiration and expiration. The Diaphragm The Diaphragm - Anatomical Position and Attachments  The diaphragm is located at the inferior-most aspect of the ribcage, filling the inferior thoracic aperture.  Acts as the floor of the thoracic cavity and the roof of the abdominal cavity.  The attachments of diaphragm can be divided into peripheral and central attachments.  It has three peripheral attachments:  Lumbar vertebrae and arcuate ligaments.  Costal cartilages of ribs 7-12.  Xiphoid process of the sternum. The Diaphragm - Anatomical Position and Attachments  The parts of the diaphragm that arise from the vertebrae are tendinous in structure, and are known as the right and left crura:  Right crus – Arises from L1-L3 and their intervertebral discs. Some fibres from the right crus surround the oesophageal opening, acting as a physiological sphincter to prevent reflux of gastric contents into the oesophagus.  Left crus – Arises from L1-L2 and their intervertebral discs.  The Diaphragm - Anatomical Position and Attachments The muscle fibres of the diaphragm combine to form a central tendon. This tendon ascends to fuse with the inferior surface of the fibrous pericardium. Either side of the pericardium, the diaphragm ascends to form left and right domes. At rest, the right dome lies slightly higher than the left – this is thought to be due to the presence of the liver. Pathways through the Diaphragm  The diaphragm divides the thoracic and abdominal cavities. Thus, any vessels that pass between the two cavities will pierce the diaphragm. There are three openings that act as conduit for these structures:  Oesophageal opening (T10 level): Transmits the oesophagus, vagus nerves, and oesophageal branches of the left gastric vessels.  Aortic opening (T12 level): Transmits the aorta, thoracic duct (a large lymphatic vessel) and azygous vein.  Caval opening (T8 level): Transmits the inferior vena cava. Actions of the Diaphragm  The diaphragm is the primary muscle of respiration.  During inspiration, it contracts and flattens, increasing the vertical diameter of the thoracic cavity. This produces lung expansion, and air is drawn in.  During expiration, the diaphragm passively relaxes and returns to its original dome shape. This reduces the volume of the thoracic cavity. Innervation and Vasculature  The halves of the diaphragm receives motor innervation from a phrenic nerve.  The left half of the diaphragm (known as a hemidiaphragm) is innervated by the left phrenic nerve, and vice versa.  Each phrenic nerve is formed in the neck within the cervical plexus, and contains fibres from spinal roots C3-C5.  The majority of the arterial supply to the diaphragm is delivered via the inferior phrenic arteries, which arise directly from the abdominal aorta.  The remaining supply is from the superior phrenic, pericardiacophrenic, and musculophrenic arteries.  The draining veins follow the aforementioned arteries. Innervation and Vasculature Other Layers Suprapleural Membrane  It is a dense fascial layer  Tent-shaped fibrous sheet  Attached laterally to the medial border of the first rib and costal cartilage.  At its apex to the tip of the transverse process of the seventh cervical vertebra.  Medially to the fascia investing the structures passing from the thorax into the neck. It  Protects the underlying cervical pleura and resists the changes in intrathoracic pressure occurring during respiratory movements. Endothoracic Fascia  Thin layer of loose connective tissue that separates the parietal pleura from the thoracic wall.  The suprapleural membrane is a thickening of this fascia. 1 Identify the muscle A.External intercostals B.Internal intercostals C.Innermost intercostal D.Subcostals E.Transversus thoracis. 2 Identify the muscle A.External intercostals B.Internal intercostals C.Innermost intercostal D.Subcostals, E.Transversus thoracis 3. Identify the muscle A.External intercostals B.Internal intercostals C.Innermost intercostal D.Subcostals E.Transversus thoracis  4 Identify the muscle A.External intercostals B.Internal intercostals C.Innermost intercostal D.Subcostals E.Transversus thoracis. 5 Identify the muscle A.External intercostals B.Internal intercostals C.Innermost intercostal D.Subcostals, E.Transversus thoracis.