Diaphragm and Intercostal Muscles

Diaphragm and intercostal muscles Skeletal System Adult Human contains 206 Bones 2 parts: Axial skeleton (axis): Skull, Vertebral column, Thoracic cage Appendicular skeleton: Bones of upper limb Bones of lower limb Structure of Typical Vertebra Body Vertebral foramen Pedicle Transverse process Spinous process Lamina Thoracic Cage -Sternum (G, sternon= chest bone) -12 pairs of ribs & costal cartilages - 12 thoracic vertebrae Sternum Flat bone 3 parts: Manubrium Body Xiphoid process The external intercostal muscle forms the most superficial layer. Its fibers are directed downward and forward from the inferior border of the rib above to the superior border of the rib below The muscle extends forward to the costal cartilage where it is replaced by an aponeurosis, the anterior (external) intercostal membrane The internal intercostal muscle forms the intermediate layer. Its fibers are directed downward and backward from the subcostal groove of the rib above to the upper border of the rib below. The muscle extends backward from the sternum in front to the angles of the ribs behind, where the muscle is replaced by an aponeurosis, the posterior (internal) intercostal membrane. Head of rib 1st rib 2nd rib Typical rib 11th & 12th Neck of rib 1st rib 2nd rib Typical rib 11th & 12th Tubercle of rib 1st rib 2nd rib Typical rib 11th & 12th Body of rib 1st rib 2nd rib Typical rib 11th & 12th Angle of rib 1st rib 2nd rib Typical rib 11th & 12th The innermost intercostal muscle forms the deepest layer. It is an incomplete muscle layer and crosses more than one intercostal space within the ribs. Action of Intercostal muscles Contraction elevates ribs and increases anteroposterior and lateral dimensions of thoracic cavity, resulting in inhalation Relaxation depresses ribs and decreases anteroposterior and lateral dimensions of thoracic cavity, resulting in exhalation ACTION: When the intercostal muscles contract, they all tend to pull the ribs nearer to one another. If the 1st rib is fixed by the contraction of the muscles in the root of the neck, namely, the scaleni muscles, the intercostal muscles raise the 2nd to the 12th ribs toward the first rib, as in inspiration. If, conversely, the 12th rib is fixed by the quadratus lumborum muscle and the oblique muscles of the abdomen, the 1st to the 11th ribs will be lowered by the contraction of the intercostal muscles, as in expiration. In addition, the tone of the intercostal muscles during the different phases of respiration serves to strengthen the tissues of the intercostal spaces, thus preventing the sucking in or the blowing out of the tissues with changes in intrathoracic pressure Intercostal vein Intercostal artery Intercostal nerve Nerve supply:  The intercostal muscles are supplied by the corresponding intercostal nerves.  The intercostal nerves and blood vessels run between the middle and innermost layers of muscles  They are arranged in the following order from above downward: intercostal vein, intercostal artery, and intercostal nerve (i.e., VAN). The intercostal nerves are the anterior rami of the first 11 thoracic spinal nerves. The anterior ramus of the 12th thoracic nerve lies in the abdomen and runs forward in the abdominal wall as the subcostal nerve. Diaphragm The diaphragm is a thin muscular and tendinous septum that separates the chest cavity above from the abdominal cavity below Chest cavity It is pierced by the structures that pass between the chest and the abdomen. The diaphragm is the most important muscle of respiration.  It is dome shaped and consists of a peripheral muscular part, which arises from the margins of the thoracic opening, and a centrally placed tendon. Abdominal cavity Right dome (cupola) Left dome (cupola) As seen from in front, the diaphragm curves up into right and left domes, or cupulae The right dome lies at a higher level, because of the large size of the right lobe of the liver Central tendon The domes support the right and left lungs, whereas the central tendon supports the heart Right cupola Left cupola Central tendon When seen from the side, the diaphragm has the appearance of an inverted J, the long limb extending up from the vertebral column and the short limb extending forward to the xiphoid process The levels of the diaphragm vary with the phase of respiration, the posture, and the degree of distention of the abdominal viscera. The diaphragm is lower when a person is sitting or standing; it is higher in the supine position and after a large meal Origin of diaphragm: Sternal part: arising from the posterior surface of the xiphoid process Costal part: arising from the deep surfaces of the lower six ribs and their costal cartilages Vertebral part: arising from upper 3 lumbar vertebrae by two crura and five arcuate ligaments (one median, two medial and two lateral arcuate ligaments) Sternal part Costal part Vertebral part The right crus arises from the first three lumbar vertebrae and the intervertebral discs The left crus arises from the first two lumbar vertebrae and the intervertebral disc Right crus Left crus Right crus has 3 special features a- It is larger, longer and stronger to overcome the resistance offered by the liver during descent of the diaphragm b- Some of its muscle fibers run up to left, to surround the oesophagus L2 L3 Right crus Left crus These fibers appear to act as a sphincter and possibly assist in the prevention of regurgitation of the stomach contents into the thoracic part of the esophagus Lateral to the crura, the diaphragm arises from the medial and lateral arcuate ligaments Medial arcuate ligament extends from the body of L2 to the tip of the transverse process of L1 Lateral arcuate ligament extends from the tip of the transverse process of L1 to the 12th rib. L2 L3 Lateral arcuate ligament Medial arcuate ligament Median arcuate ligament The medial borders of the two crura are connected by a median arcuate ligament, which crosses over the anterior surface of the aorta Note: Medial arcuate ligaments lie across the upper part of psoas major Lateral arcuate ligaments lie across the upper part of the quadratus lumborum Psoas major Quadratus lumborum Insertion of diaphragm : All muscle fibers of the diaphragm converge on a strong aponeurosis called the central tendon Major Openings of the diaphragm Opening Level Structures passing through it Aortic (middle) T12 Aorta Thoracic duct Azygos vein Oesophageal opening (Left) T10 Esophagus Right and left vagus nerves Vena Caval (Right) T8 Inferior vena cava Right phrenic nerve Mnemonic: I ate(8) 10 Eggs At 12 I ate(8): I for IVC at T8 10 Eggs: E for esophagus at T10 At 12: A for Aorta at T12 Right lung Aorta Esophagus IVC Heart Superior view of the diaphragm Nerve Supply : Motor nerve supply: The right and left phrenic nerves (C3, 4, 5) Sensory nerve supply: The central portion of the diaphragm is from the phrenic nerve and the periphery of the diaphragm is from the lower six intercostal nerves. Arterial supply: Superior phrenic arteries (from thoracic aorta) Inferior phrenic arteries (from abdominal aorta) Musculophrenic Pericardiophrenic artery (from internl thoracic artery) Phrenic nerves (C3, 4, 5) Abdominal aorta Inferior phrenic arteries are branches of abdominal aorta Subclavian artery Internal Thoracic Artery  The internal thoracic artery supplies the anterior wall of the body from the clavicle to the umbilicus It is a branch of the first part of the subclavian artery in the neck  It descends vertically behind the costal cartilages, a fingerbreadth lateral to the sternum  It ends in the sixth intercostal space by dividing into: Superior epigastric artery Musculophrenic artery Function of the diaphragm 1. Muscle of inspiration 2. Muscle of abdominal straining: The contraction of the diaphragm is raising the intra abdominal pressure 3. Weight-lifting muscle: 4- Thoracoabdominal pump: Pump for blood and lymph