Using the Sectra table, you will identify the structures of the thorax. Bolded terms are in the objectives for this lab.
The thorax
“The heart and lungs are fragile organs, and the main function of the thorax is to house and protect them. The protective function of the thoracic wall is combined with mobility to accommodate volume changes during respiration. These two dissimilar functions, protection and mobility, are accomplished by the alternating arrangement of the ribs and intercostal muscles. The superficial fascia of the thorax contains the usual elements that are common to superficial fascia in all body regions: blood vessels, lymph vessels, cutaneous nerves, and sweat glands. In addition, the superficial fascia of the anterior thoracic wall contains the mammary glands, which are highly specialized organs unique to the superficial fascia of the thorax.“ – Grant’s Dissector 16th ed.
Review the bones of the thorax in the VH Dissector:
- Identify bones of the thorax: scapula, clavicle, the parts of the sternum (manubrium, body, and xyphoid process), costal cartilages, the true ribs (vertebrosternal ribs/ribs 1-7), the false ribs (ribs 8-12). Ribs 8-10 are also known as vertebrochondral ribs, while ribs 11-12 are also known as the floating ribs/vertebral ribs.
The Intercostal muscles
Begin your dissection (select this button at any time to start over):
As you identify and dissect muscles, you should review their origin, insertion, innervation, and action(s). As you identify and dissect neurovascular structures, you should review their pathways.
If you are having trouble highlighting narrow structures (arteries, veins, nerves), you can search for them by selecting the Anatomy tab, typing the name of the structure in the search box, and selecting the sun icon next to the listed structure. You can dissect these structures by selecting the eye icon.
- Dissect the upper limb muscles that originate in the thorax: the pectoralis major, pectoralis minor, serratus anterior, and latissimus dorsi
As you highlight a structure, note that the structure will also be highlighted in the multiplanar reconstructed (MPR), or cross-sectional images in the leftmost pane. All structures should be identified on the MPR images. Using three fingers, scroll through the MPR images to understand the three-dimensional relationships between different structures as you work though the lab. Structures that are difficult to identify in the MPR images will have additional links to assist you.
Q1: Using your knowledge of muscle origins/insertions, what upper limb muscles assist in inspiration? What is the primary muscle of respiration? (answer)
- Identify the external intercostal muscles in the lateral intercostal spaces
- Identify the interal intercostal muscles deep to the external intercostals (you don’t need to dissect the external intercostal muscles, as the internal intercostal muscles fill the intercostal spaces anteriorly to the sternum
- The innermost intercostal muscles are not visible on the model or MPR images. Use the diagram to understand the relationship between the intercostal muscles
The thoracic wall and posterior mediastinum
Use the following view of the thorax with viscera removed to understand the structures of the thoracic wall:
- Rotate the model to view the thoracic region from the inferior side. Identify the and dissect the diaphragm
- Identify the parts of the aorta: ascending aorta, aortic arch, and descending aorta (thoracic aorta) (MPR)
- Identify the superior vena cava, brachiocephalic trunk and subclavian arteries (note the asymmetric branching pattern) (MPR)
- Identify the brachiocephalic veins and the subclavian veins (MPR)
- Identify the internal thoracic arteries and internal thoracic veins
- The anterior intercostal arteries and anterior intercostal veins branch off of the internal thoracic arteries. The internal thoracic arteries bifurcate into the musculophrenic artery and superior epigastric artery below the level of the 6th rib. These vessels are not visible on the model
The medial part of the thoracic cavity is the mediastinum. Review the boundaries and subregions of the mediastinum:
- On the posterior thoracic wall, identify the posterior intercostal arteries originating from the thoracic aorta
- Identify the intercostal nerves (identified as thoracic nerves on the model)
- Identify the posterior intercostal veins, which are tributaries of the azygos vein on the right side and the hemiazygos veins and accessory hemiazygos veins on the left side. The accessory hemiazygos vein isn’t visible on the model, and is a variable structure. Use the diagram below to identify the typical arrangment of the azygos and hemiazygos veins
- Identify the arch of the azygos vein where it drains into the superior vena cava
- Identify the thoracic duct
- The sympathetic trunks and splanchnic nerves are not visible on the model. Identify them on the diagram below
The mediastinum and external heart
Use the following view to examine the external heart and neurovasculature of the thorax:
- Identify and dissect the thymus anterior to the great vessels of the heart
- Identify the phrenic nerves
- Identify the vagus nerves and the recurrent laryngeal nerves. Identify the ligamentum arteriosum and note its position relative to the left recurrent laryngeal nerve (MPR)
- Identify the pulmonary trunk artery, pulmonary veins, and the esophagus (MPR)
- The bronchial arteries and esophageal plexus are not visible on the model, identify them on the images below
Q2: What is the position of the esophagous relative to the heart? What is the position of the esophagous relative to the aorta in the superior mediastinum, and is it different from the position in the posterior mediastinum? (answer)
The pericardium and pleura are not visible on the model. Examine the diagrams below to understand the relationship between the endothoracic fascia, the parietal and viscerial pleura, and the fibrous and serous pericardium.
Q3: During a thoracentesis, what intercostal space is the needle inserted into to access the costodiaphragmatic recess? In order from superficial to deep, what muscle/tissue layers will the needle pierce? What is the name of the potential space where the sample is collected? (answer)
- Identify the chambers of the heart visible externally: left atrium, right atrium, left ventricle, right ventricle (the external surface of these chambers will all be labeled “myocardium of the ___”)
- While they cannot be identified on the model, use your anatomical knowledge to identify the surfaces of the heart: sternocostal (anterior) surface, diaphragmatic (inferior) surface, left pulmonary surface, right pulmonary surface, apex of heart, base of heart
- Identify the auricles of the left and right atrium, and the anterior interventricular sulcus (they cannot be individually highlighted)
- Dissect the diaphragm, esophagous, inferior vena cava, and abdominal and thoracic aortas and rotate the heart to view the posterior interventricular sulcus (this cannot be individually highlighted, but is the groove in between the left and right ventricles on the posterior side of the heart)
- Identify the coronary sulcus on the anterior and posterior sides of the heart (this cannot be highlighted, but is the groove between the atria and ventricles of the heart)
Use the diagram below to understand the oblique pericardial sinus and the transverse pericardial sinus. Locate the features of the heart corresponding to the sinuses (hint: use the great vessels as landmarks)
- Identify the right coronary artery and left coronary artery where they branch off the ascending aorta (MPR)
- Identify the branches of the left coronary artery:
- the circumflex artery
- the anterior interventricular artery (also known as the left anterior descending artery)
- Identify the right marginal artery where it branches off of the right coronary artery
- The posterior interventricular artery (also known as the posterior descending artery), sinoatrial nodal artery, anterior right atrial artery, and atrioventricular nodal artery are not visible on the model. Identify them on the figures below
Q4: Why is the posterior interventricular artery NOT known as the right posterior descending artery? (answer)
- On the posterior side of the heart, identify the coronary sinus
- Identify the veins that drain into the coronary sinus: the great cardiac vein, middle cardiac vein, and middle cardiac vein
- anterior cardiac veins are not visible on the model. Identify them in the images below
Internal heart
Use the following view to examine the internal heart:
Note that the MPR pane images have been adjusted so that the four chambers are more fully visualized. With the full cadaver visible, look at the blue plane on the model and top MPR image.
Q5: Are you looking at this image visualized from the inferior side or from the superior side? (answer)
- On the top MPR image, identify the four chambers of the heart. Pay special attention to the left/right orientation.
“Skin” the model by selecting the Skin button and taking the transparency to zero. Remove the colored plane by selecting the Panes button and then the first Filled button.
Because the model cannot be “opened” like a physical cadveric heart, you will need to rely on the MPR images to visualize the relationships between many of the internal structures.
- Identify the interatrial septum and interventricular septum on the MPR images
- On the model, dissect the subepicardial fat to clearly view the the muscular layers of the heart
- On the model, dissect the myocaridium of the right atrium and the “right atrium”, and identify the pectinate muscles. Note on the MPR images how they line part of the inner surface of the right atrium
- Identify the crista terminalis, dividing the area of the atrium covered in pectinate muscles from the smooth part of the atrium
- Dissect the pectinate muscles and crista terminalis, and identify the fossa ovalis on the interatrial septum
- Identify the superior vena cava and the valves of the coronary sinus and inferior vena cava to understand where they open into the right atrium (opening of the superior vena cava, opening of the inferior vena cava, and opening of the coronary sinus)
- Identify the sinuatrial node
- Identify the anterior cusp, posterior cusp, and septal cusp of the tricuspid valve (the valve is in the open position)
Q6: What is the embryological origin of the fossa ovalis? What was the function of this embryological structure? (answer)
- Dissect the myocardium of the right ventricle. Identify and dissect the trabeculae carneae of the right ventricle.
- Dissect the right ventricle and identify anterior papillary muscle and septal papillary muscle of the right ventricle (the posterior papillary muscle is not visible on the model)
- The chordae tendineae (“tendinous cords”) connect the cusps of the tricuspid valve to the papillary muscles, and are not visible on the model
- Identify the septomarginal trabecula (moderator band) connecting the anterior papillary muscle to the interventricular septum
- Identify and dissect the conus arteriosus
- Identify the semilunar cusps of the pulmonary valve: anterior, right, and left (they are only partially intact on the model)
- Observe the gaps on the model where the pulmonary veins drain into the left atrium
- Dissect the myocardium of the left atrium and the left atrium
- Identify the anterior cusp and posterior cusp of the mitral valve (also known as the bicuspid valve)
- Dissect the myocardium of the left ventricle and the “left ventricle”
- Identify the trabeculae carneae, anterior papillary muscle, and posterior papillary muscle of the left ventricle
- Identify the semilunar cusps of the aortic valve: right, left, and posterior
Q7: What is the function of the chordae tendineae and papillary muscles? (answer)
The lungs
Use the following view to examine the lungs:
Review the orientation of aorta and esophagus relative to the trachea and lungs, then dissect the aorta and esophagus. Review the parts of the pleura.
Q8: Are the lungs in the pleural cavity? (answer)
- Identify the trachea. The place where it bifurcates (and the location of the carina) is missing from the model, but identify the right main bronchus and left main bronchus
- Identify the surfaces of the lungs: costal, mediastinal, diaphragmatic, and apex
- Identify the superior lobe and inferior lobe on both lungs, and the middle lobe of the right lung
- The superior and interior lobes are separated by the oblique fissure, while the middle lobe of the right lung is further separated from the superior lobe by the transverse fissure
- Dissect the trachea and left lung to view the mediastinal surface of the right lung
- Identify the structures of the hilum: lobar (sedondary) bronchi, pulmonary arteries, pulmonary veins
- The pulmonary ligament is not visible on the model. Identify it on the diagram below
- The impressions of the right lung can’t be highlighted, use the images below to identify them: cardiac, esophagus, arch of the azygos vein, superior vena cava
- Identify the cardiac notch and lingula of the superior lobe of the left lung using the diagram below (they cannot be highlighted on the model)
- Dissect the aorta, esophagus, trachea, and right lung to view the mediastinal surface of the left lung
- Identify the structures of the hilum: lobar (sedondary) bronchi, pulmonary arteries, pulmonary veins
- The pulmonary ligament is not visible on the model. Identify it on the diagram below
- The impressions of the left lung can’t be highlighted, use the images below to identify them: cardiac, aortic arch, thoracic aorta
Q9: Describe and contrast pneumothorax, hemothorax, hydrothorax, chylothorax, and pyothorax. (answer)
End of Sectra activity
Answers to activity questions
Below are answers to questions asked during the activity. Clicking the ‘back to lab’ link below each answer will take you back to the question (you may need to scroll up a little to view the question again).
Q1: Using your knowledge of muscle origins/insertions, what upper limb muscles assist in inspiration? What is the primary muscle of respiration?
- Upper limb muscles that assist in active (forced) inspiration include: serratus anterior, pectoralis major, and pectoralis minor
- The diaphragm is the primary muscle of respiration
Q2: What is the position of the esophagous relative to the heart? What is the position of the esophagous relative to the aorta in the superior mediastinum, and is it different from the position in the posterior mediastinum?
- The esophagus is posterior to the heart
- The esophagus is posterior to the aorta in the superior mediastinum, and anterior to the aorta in the posterior mediastinum
Q3: During a thoracentesis, what intercostal space is the needle inserted into to access the costodiaphragmatic recess? In order from superficial to deep, what muscle/tissue layers will the needle pierce? What is the name of the potential space where the sample is collected?
- The 9th intercostal space (in the midaxillary line)
- From superficial to deep: external intercostal muscle, internal intercostal muscle, innermost intercostal muscle, endothoracic fascia, parietal pleura
- Fluid samples are collected from the pleural cavity, the space between the parietal pleura and the visceral pleura
Q4: Why is the posterior interventricular artery NOT known as the right posterior descending artery?
- The posterior interventricular artery is variable, originating off the right coronary artery in 67% of people and the left coronary artery in 33% of people. Conversely, the anterior interventricular artery always originates from the left coronary artery, giving it the synonymous name of left anterior descending artery, or LAD
Q5: Are you looking at this image visualized from the inferior side or from the superior side?
- As in this case, cross-sectional images are typically viewed from the inferior side
Q6: What is the embryological origin of the fossa ovalis? What was the function of this embryological structure?
- The embryological origin of the fossa ovalis is the foramen ovale. During fetal development, the foramen ovale is part of a set of structures that connects the left and right atria, allowing blood to bypass pulmonary circulation
Q7: What is the function of the chordae tendineae and papillary muscles?
- The papillary muscles contract just before ventricular contraction, putting tension on the chordae tendineae and preventing prolapse of the atrioventricular (tricuspid and bicuspid) valves
Q8: Are the lungs in the pleural cavity?
- No, the pleural cavity is the potential space between the parietal and visceral pleurae, filled with a thin layer of serous fluid
Q9: Describe and contrast pneumothorax, hemothorax, hydrothorax, chylothorax, and pyothorax.
- Each of these conditions results from entry of a substance into the pleural cavity:
- Pneumothorax (air): typically from either a penetrating wound (such as from a bullet) or the rupture of a pulmonary lesion, resulting in a collapsed lung due to the loss of negative air pressure
- Hydrothorax (fluid): may result from pleural effusion (escape of fluid into the pleural cavity)
- Hemothorax (blood): commonly resulting from injury to a major intercostal or internal thoracic vessel
- Chylothorax (lymph): pleural effusion of lymph from the thoracic duct or one of its tributaries
- Pyothorax (pus): also known as pleural empyema, results from bacteria such as from pneumonia, injury, or chest surgery