MUSCLES OF THE THORAX PROF. RAMIREZ 1 Thorax • Thorax refers to the entire chest • Functions: – Protect organs in chest and upper abdomen – Provides support for bones of upper limbs • Bony cage flattened from front to back • Formed by: – Sternum – Ribs – Costal cartilages – Bodies of thoracic vertebrae. 2 Pectoralis Major O: Clavicular Head: Medial clavicle Sternal Head: Sternum and the upper costal cartilages I: Lateral lip of the bicipital groove A: Adduction, medial rotation, and horizontal adduction of the arm. The clavicular head also causes flexion of the arm. Secondarily depresses and protracts the scapula. **Reversed muscle action causes elevation of the trunk, lateral deviation, and ipsilateral rotation. N: Medial and Lateral Pectoral nerves 3 Pectoralis Minor • When contracting it pulls on the coracoid process and pulls scapula in such a manner that the lateral border is pulled in toward the lateral body wall and the medial border moves away from posterior body wall. – This movement is called lateral tilt. • Rounded shoulders is a common postural condition in which the scapulae are protracted and depressed and the humeri are medially rotated. – Given the pec minor’s action of both protraction and depression, when pec minor muscles are tight, they can contribute to this condition. • By elevating ribs 3-5, this muscle can expand the ribcage during inspiration (accessory muscle of inspiration) 4 Pectoralis Minor O: Anterior borders of ribs # 3 through 5 I: Coracoid process of the scapula A: Protracts, Depresses, and downwardly rotates the scapula **Reversed muscle action rd includes elevation of the 3 th through 5 ribs N: Medial pectoral nerve 5 Subclavius • If clavicle is fixed to the scapula, then subclavius can also depress the scapula at the scapulocostal joint • Many believe main function is to act as a fixator of the clavicle during arm/shoulder movements. • Common entrapment site for nerves of brachial plexus and subclavian artery called costoclavicular syndrome 6 Subclavius muscle is “under” the clavicle O: 1st rib I: Inferior surface of the clavicle A: Depression of the clavicle and Elevation of the 1st rib N: Nerve to the subclavius from the brachial plexus 7 Serratus anterior (ventralis) • O-Ribs 1-9 • I- Scapula • A- Protract, Rotate scapula • N-Long Thoracic 8 External Intercostals • Oriented in the same direction as the external oblique abdominal muscles. – Appear to be extensions of external obliques • Involved in respiration (inspiration) • These muscles should be addressed in any client who has a respiratory condition. • This is the meat which is eaten when one eats spare ribs. 9 O: Inferior borders of ribs 1-12 I: Superior border of the rib below A: Elevation of ribs 2-12 N: Intercostal nerves 10 Internal Intercostals • Oriented in the same direction as fibers of the internal abdominal obliques. • Generally thinner then external intercostals. • Involved in respiration (expiration) • There is another layer of muscles called the innermost intercostals which are located deep to the internal intercostals. 11 Internal Intercostals located between the ribs and internal to external intercostals O: Superior border of the rib below I: Inferior border of the rib above A: Depresses ribs 1-11 N: Intercostal nerves 12 Transversus Thoracis • Superior fibers run primarily vertically but inferior fibers run horizontally • Located internally i.e. located within thoracic cavity • Primary role is as a respiratory muscle. 13 Transversus Thoracis Runs transversely across the thoracic region O: Internal surfaces of the sternum, xiphoid and adjacent costal cartilages I: Internal surfaces of costal cartilages 2-6 A: Depression of ribs 2-6 N: Intercostal nerves 14 Diaphragm • Separates the thoracic and abdominal cavities. • Number of openings to allow passage of structures between thoracic and abdominal cavities. – Largest openings for esophagus, aorta and inferior vena cava • Only muscle that must contract for quiet, relaxed inspiration. • Usually under both conscious and unconscious control. • Innervation is phrenic nerve composed of spinal nerves C3, 4, 5. – “C3, 4, 5 keeps the diaphragm alive!” • Clinically a Hiatal hernia is when part of the stomach herniates through the diaphragm into the thoracic cavity. 15 Diaphragm O: Internal surfaces of ribcage, sternum and spine I: Central tendon of diaphragm A: Increases volume of thoracic cavity during inspiration N: Phrenic nerve 16 Diaphragm openings • The diaphragm has three major openings. • The esophageal opening in the right crus transmits the esophagus and vagus nerves. • The aortic opening lies posterior to the crura and transmits the aorta, the thoracic duct and greater splanchnic nerves, and occasionally the azygos vein. • The foramen for the inferior vena cava, in the right half of the central tendon, transmits the vena cava, right phrenic nerve, and lymphatic 17 vessels. Neurovascular Bundle of Intercostal Muscles • VAN (vein, artery, nerve) – Intercostal vein – Intercostal artery – Intercostal nerve • Sit in Subcostal Groove • Between Internal Intercostal and Innermost intercostal layer Nerves of the Thoracic Wall • The 12 pairs of thoracic spinal nerves supply the thoracic wall. • They divide into anterior and posterior primary rami • The anterior rami of nerves T1 to T11 form the intercostal nerves that run along the extent of the intercostal spaces. • The anterior ramus of nerve T12, coursing inferior to the 12th rib, is the subcostal nerve • The posterior rami of thoracic spinal nerves 19 pass posteriorly supplys the joints, muscles, and skin of the back in the thoracic region dermatomes 20 CLINICAL • vertebrocostal trigone • a triangular area in the diaphragm near the lateral arcuate ligament that is devoid of muscle fibers; it is covered by pleura superiorly and by peritoneum inferiorly. • congenital diaphragmatic hernia • absence of the pleuroperitoneal membrane (usually on the left) or an enlarged Morgagni's foramen which allows protrusion of abdominal viscera into the chest. 21 Intercostal Nerve Block • Local anesthesia of an intercostal space is produced by injecting a local anesthetic agent around the intercostal nerves between the paravertebral line and the area of required anesthesia. • In this procedure, an intercostal nerve block, involves infiltration of the anesthetic around the intercostal nerve trunk and its collateral branches. 22 Dyspnea: Difficult Breathing • When people with respiratory problems (e.g., asthma) or with heart failure struggle to breathe, they use their accessory respiratory muscles to assist the expansion of their thoracic cavity. • They lean on their knees or on the arms of a chair to fix their pectoral girdle so these muscles are able to act on their rib attachments and expand the thorax. 23 Needle thoracocentesis • Performed in patients in whom a life threatening tension pneumothorax is suspected. • A needle is inserted into the second intercostal space in the midclavicular line on the the side of the tension pneumothorax, with the patient in an upright position. • A sudden escape of air is heard when the needle enters the pariental pleura. A chest tube is inserted after this procedure. 24 25 Subclavian vein cannulation • Is performed with the patient supine, the head turned slightly to the opposite side, and the arms placed by the side. • The central venous needle is then inserted from the inferior edge of the clavicle towards the suprasternal notch. • The needle is directed so that it passes just below the posterior border of the clavicle; care must be taken to avoid downward direction of the needle, which may cause a 26 pneumothorax. Gentle aspiration of the syringe is performed whilst the needle is being advanced until the subclavian vein is punctured END 27 .