Anatomy 512B
Human Anatomy of the Thorax, Back and Upper Extremity
Unit II
Instructors:
Julie Rosenheimer
Scott Lozanoff
Beth Jones
Sandy Tsuhako
Suzanne Yandow
Lecture: Fridays at 1:30 in B-206
Dissection: A-206
Dec. 1, 2000 - Mar 2, 2001
1. SKIN & SUBCUTANEOUS TISSUE OF THORAX AND BACK
OBJECTIVES RESOURCES
1. Lymphatic System
a. State the general function of the system. 1a,b. Discussion 1-1.
b. Describe consequences of blockage.
c. Trace alternate lymphatic drainage pathways 1c. Netter, Plate 169;
from the mammary gland. Discussion 1-1.
d. Explain route of drainage back to the
venous system.
2. Thoracic spinal nerve
a. Identify anterior, lateral and posterior 2a,b. Netter, Plates 166, 178, 240,
cutaneous branches. 241; Discussion 1-2.
b. Diagram and label:
-dorsal and ventral roots
-dorsal root ganglion
-dorsal and ventral rami
-spinal nerve
-cutaneous branches
c. Define components: 2c,d. Discussion 1-2.
-somatic motor
-postsynaptic sympathetic
-general sensory
d. Locate nerve cell bodies of each
component.
e. Define a dermatome. Netter, Plate 150; Discussion 1-2.
3. Skin and superficial fascia
a. Understand the difference between dermis and
epidermis and the role of each.
b. Describe superficial fascia b. Discussion 1-3
and the types of structures found in this Also from
tissue: observation.
-cutaneous nerves
-lymphatics
-blood vessels and glands.
DISSECTION
Note: you will need AT LEAST two (2) fresh scalpel blades for this dissection.
1. Feel the sternal notch and with a scalpel, CUT through the skin to the bone of the sternum; EXTEND this cut caudally to the palpable xiphoid process at the inferior end of the sternum. As this cut is made, gauge the thickness of the skin. No harm can be done in making this initial cut. Of what tissue types is skin composed?
2. MAKE PARALLEL CUTS through the skin about 3 to 4 inches apart perpendicular to the sternum. Begin these cuts at the midline incision and extend them laterally as far as feasible. (DO NOT continue these parallel cuts in a caudal direction or you will sever the lateral cutaneous nerves (see below).) SUPERIORLY these cuts should include the skin along the superior edge of the CLAVICLE to the AXILLA. INFERIORLY the lowest cut should extend from the XIPHOID PROCESS along the COSTAL MARGIN laterally to about the MIDAXILLARY LINE. There is no great value in cutting around a nipple for the sake of preserving it. All outlined strips of skin on the thorax should be removed in this fashion. In this way, all dissectors can work simultaneously.
3. With the forceps holding the edge of the skin at the midline, CUT the skin from the underlying superficial fascia about one inch laterally. In a fat body, do not worry about some of the fat clinging to the skin. In a very thin body, make the separation as clean as possible. What is the major component of the superficial fascia?
4. After skin is freed from the midline and you have examined the dermis on its underside, return to the midline and find the separation plane between the superficial fascia and the underlying investing fascia. CONTINUE this separation laterally, until you catch up to where you left off. How do the superficial and investing fasciae differ?
5. Now, with a blunt probe, continue the separation of the skin and superficial fascia as a unit. Look for the anterior cutaneous nerves (for the skin) as they travel from the deeper musculature through the superficial fascia. A cutaneous nerve must come through a hole in the muscle, and generally is noticeably accompanied by a darkly-stained vein. The nerves are tough--easy to cut, but hard to break. The clues just given should help you avoid mistaking connective tissue strands for cutaneous nerves. What are the components of a cutaneous nerve and what are their targets?
Drawings
6. With a scalpel make a stab wound in the flap of skin and superficial fascia large enough for one or two fingers . Insert a finger in the hole and pull very hard on the flap. As the flap is pulled toward you, the separation plane between the superficial and investing fasciae weakens and is easily CUT with long strokes of the scalpel. While cutting, hold the blade perpendicular to the body, with the edge facing you -- slicing or damaging the skin flaps does not matter as they can be discarded.
7. Bluntly separate and clean several of the anterior cutaneous nerves. Next, rapidly remove the rest of the skin and superficial fascia with the scalpel for some distance toward the side of the body.
8. Laterally, switch once more to a blunt probe in separating the superficial fascia from the musculature; now watch for the lateral cutaneous nerves entering the deep surface of the flap. Save a few of these as stubs as well.
* The figure shows the idealized pattern of cutaneous nerves on the front of the thorax. Be satisfied with one or two examples of each set, but keep all cutaneous nerves encountered.
Drawings
9. Turn over the body and WITH A FRESH SCALPEL BLADE make parallel cuts through the skin on the back similar to what was done anteriorly. The cuts can be extended SUPERIORLY onto the base of the skull (even with the superior aspect of the ears). Cuts should extend INFERIORLY along the iliac crest to the inferior aspect of the sacrum.
10. IT IS SAFEST TO START TO SKIN THE BACK AT THE LEVEL OF THE SCAPULAR SPINE WHERE THE SUBCUTANEOUS TISSUE IS THE THINNEST. Be careful in removing the superficial fascia and, particularly, in identifying the separation plane between that layer and the underlying musculature. As you skin, be sure that you recognize the edges of the large trapezius and latissimus dorsi muscles. Prior knowledge of the direction in which the muscle fibers of these muscles travel is useful so be sure to have an open atlas by your side. Anticipating these points will aid in the preservation of these underlying muscles.
11. Remove the flaps of skin in the same way as was done anteriorly. Remember to make the stab wound and to pull on the flap as hard as possible. FREE and PEEL BACK the superficial fascia as well. Watch for the posterior cutaneous nerves which generally poke through the muscles about 1-2 inches from the midline, particularly high on the back. Save each one noticed, although frankly, the posterior nerves are often hard to find. Note that the subcutaneous tissues on the back are much tougher than on the front, making nerve-finding more difficult.
12. Continue to work in a caudal and cephalic direction, where the subcutaneous tissue gets thicker. Be sure to skin the back of the head from an inferior-to-superior direction to avoid damaging an artery and nerve that we will study on a later dissection. They can easily be accidentally removed if you begin to skin the scalp from the base of the skull working inferiorly. There is a great deal of fat in the small of the back and above the hip bones (perhaps 3-4 inches in a very fat body). Remove all this but stop at the shiny thoracolumbar aponeurosis low in the back. It is easy to unintentionally remove some of the muscle and aponeurosis.
13. Continue the removal of the skin flaps laterally until you meet the anterior flaps, and the skin and superficial fascia can be discarded.
Drawings
DISCUSSION
1-1 - The Lymphatic System
The primary function of the lymphatic vessels is to return plasma proteins and water which have escaped from the blood capillaries back into the blood-vascular channels. The return of the large molecules of plasma proteins serves to maintain osmotic equilibrium. The lymphatic system also provides an important defense mechanism for the body via its production of lymphocytes. In addition it provides a mechanism for the spread of cancer cells.
Lymphatic capillaries. Lymphatic capillary networks are very widely distributed, particularly within the soft connective tissues. They are particularly abundant in the dermis of the skin, which we dissect in this lab, and in the mucosa and submucosa of the digestive and respiratory tracts. Interestingly, they are absent in the central nervous system and the eyeball, and their existence in voluntary muscle is questionable.
Lymphatic capillaries begin blindly as cul-de-sacs called lacteals. They richly anastomose in plexuses and unite to form increasingly larger ducts which ultimately deliver their contents (lymph) into the veins. Lacteals are much more permeable than the blood capillaries, although the exact mechanism enabling the entry of macromolecules is not fully understood.
Lymphatic ducts. Histologically, the larger lymphatic channels resemble veins. Although the lymphatic channels associated with the skin cannot be seen with the naked eye, the larger lymph ducts, such as the thoracic duct, which we will be dissecting in a later lab, are dissectable. (The thoracic duct ultimately receives lymph from the entire body with the exception of the right half of the head, the right upper limb and the right upper quadrant of the thorax, all of which drain into the right lymphatic duct.) The bulk of the lymph returned to the venous system from the thoracic duct enters at the junctions of the left jugular and subclavian veins in the neck. See the diagram below.
Other return routes are possible but not fully elucidated. Evidence (lymphography) suggests that some lymph returns to the veins found within lymph nodes and that other connections may exist between lymphatics and other veins, e.g., the azygos system.
Mechanism of lymph flow. Lymph flow is a one-way street. The existence of numerous valves permits flow only toward the venous system. It is questionable in the human whether the smooth muscle of the larger ducts is a significant driving force. In general, propulsion is dependent upon the milking action of neighboring structures such as voluntary muscle contraction, pulsations of adjacent arteries or other smooth muscle contraction, e.g., digestive tract, urinary bladder, etc. Of some significance also is the negative intrathoracic pressure created by action of the respiratory muscles. Thus, the existence of valves, movement of adjacent structures and negative intrathoracic pressure are the three most essential factors in propelling lymph within its channels.
Lymph. Lymph is defined as the fluid within lymphatic channels. It is mostly water, but contains other materials that vary in amounts depending on their source. On average, lymph contains less protein than is found in the blood, although it contains varying amounts of all the non-cellular constituents of the blood plus lymphocytes. Lymph is clear in the extremities but is milky from the digestive tract. Lymph from any organ mirrors the metabolic activity of that organ. From the liver, for example, it is rich in plasma proteins. Lymph from glandular tissue generally contains secretion products, e.g., lymph from the testis is rich in testosterone, lymph from the ovary is rich in estrogens, etc. It is premature to state how significant a contribution lymphatics make to the delivery of such secretions, but it is probably greater than is generally appreciated.
Lymph nodes. In general, all lymph passes through one or more lymph nodes before it enters a vein. It is of obvious clinical significance to know to which group of nodes lymph from a particular area drains. Also, the location of lymph nodes is of clinical significance because of their role in the immune response (via their production of antibodies to fight infection) as well as in the spread of cancer (cancers that spread through the lymphatic system tend to migrate (metastasize) first to lymph nodes where they grow). It should be understood that all cutaneous lymph, i.e., lymph draining from the skin, below the head and neck drains primarily into the axillary or inguinal nodes. The circumference of the trunk at the level of the umbilicus defines the cutaneous areas drained to these nodes, i.e., above to the axillary nodes, below to the inguinal nodes. There are, of course, anastomotic connections so that it is possible under unusual circumstances for lymph from the mammary gland, for example, to drain into the superficial inguinal nodes. Superficial nodes are nodes located superficial to the investing fascia in the subcutaneous tissue. Deep nodes are nodes which lie deep to the investing fascia.
Drainage of the mammary gland. As one very important example, you should understand in detail the lymph drainage from the mammary gland. The main lymphatic channels pass to the pectoral, subscapular, central and apical nodes; all members of the axillary group. Secondary routes exist along the internal thoracic artery to the parasternal nodes; anastomatic connections across the front of the chest may result in metastases to the opposite breast. Also, lymphatic channels from the breast to the abdominal wall with deep connections to the liver lymphatics may account for metastases to liver or upper abdominal wall. (Other less common routes are also possible.)
Lymphoid tissue. The term lymphoid should be used to describe tissues containing significant populations of lymphocytes, e.g., lymph nodes, thymus, spleen, tonsils, appendix and Peyer's patches. When one discusses the lymphatic system, the lymphoid organs are usually included.
1-2 - Nervous System
Your introduction in this course to the nervous system is a demonstration of several cutaneous nerves lying in the subcutaneous tissues of the trunk.
The nervous system is subdivided into the Central Nervous System (CNS--the brain and spinal cord), and the Peripheral Nervous System (PNS-- the ganglia and "nerves"). It is the PNS which is of primary importance to the study of gross anatomy.
The nervous system is mostly composed of nerve cells also known as neurons. Each neuron has a large cell body (soma), which contains the nucleus, and other organelles; a single, usually very long process is called an axon, and shorter, highly branched and often numerous, processes are called dendrites. In gross anatomy the axons in particular are studied in some detail because they are bundled to create the nerves of the PNS.
Nerve cells are either motor neurons (taking information away from the CNS to innervate muscle or glands), or sensory neurons (taking information towards the CNS from sensory receptors in the body's tissues).
Cell bodies for each component are always collected in certain definite sites. Knowledge of these sites is emphasized in gross anatomy as a means of helping to make the structure of the nervous system more understandable.
The PNS can be easily classified in the following manner:
--Spinal nerves innervate tissues of the body wall of the trunk and of the trunk's
appendages.
--Cranial nerves innervate the head in the adult and also those structures developed in the
embryonic head that have subsequently migrated into the neck or shoulder region.
--Autonomics supply smooth m., cardiac m., or glands. Some autonomic axons travel with the spinal nerves and some travel with particular cranial nerves; other autonomic fibers have their own pathways.
Spinal nerves: The cutaneous nerves exposed in this first dissection are the terminal branches of spinal nerves, and contain those components needed to innervate the skin: (a) general sensory (from touch, pressure, pain and temperature receptors, for example), and (b) postganglionic sympathetics (to smooth muscle of sweat glands, hair follicles and blood vessels).
Cutaneous nerves follow a pattern of innervation known as dermatomes. A dermatome is the strip of skin receiving sensory innervation from a single spinal nerve (i.e., a single dorsal root or dorsal root ganglion). Adjacent dermatomes overlap, so that destruction of one dorsal root does not produce anesthesia of its dermatome (but does produce reduced sensation), whereas destruction of two adjacent dorsal roots does produce an area of complete insensitivity in the region of overlap. Dermatomes in the thorax correspond closely to the territory innervated by the intercostal nerves, since the ribs keep the spinal nerves from forming nerve plexuses, as occurs above and below the rib cage.
All spinal nerves are alike, that is they carry the same three components. Besides being composed of axons from the two types of neurons just mentioned (ie, sensory and postganglionic sympathetic), all spinal nerves also contain axons from somatomotor neurons (these innervate skeletal muscle). The cell bodies of these three components are found in different places in the nervous system. Somatomotor cell bodies are found in the ventral horn of the spinal cord; cell bodies of general sensory neurons associated with the spinal cord are located in the dorsal root ganglion; the cell bodies of the postsynaptic sympathetics are found in the sympathetic trunk and the presynaptic cell bodies are found in the lateral horn of the spinal cord between T1 and L2. In general, autonomic fibers are more confusing and will be discussed in more detail at a later time.
Note in the following diagram the structure of a spinal nerve, its components, and the locations of the components’ cell bodies.
1-3 - Superficial Fascia
The subcutaneous tissue is often referred to as superficial fascia. It contains varying amounts of fat and collagen fibers which attach to the dermis and blend at a deeper level with the investing or deep fascia. The term "investing fascia" is applied to the outermost layer of fascia investing striated muscle, bone, aponeuroses and glands. The fat of superficial fascia lies between fibrous septa which give an irregular honeycomb effect, with the fat lying in various-sized locules. This is rather striking in the region of the mammary gland where these septa have been traditionally known as Cooper's ligaments. These are simply exaggerated examples of the fibrous septa found in other areas. As one proceeds deeper, that is, towards the investing fascia, the superficial fascia usually becomes more and more fibrous. When removing the superficial fascia from the cadaver, you should note that the plane of cleavage is between its fibrous layer and the investing fascia, and that the fatty and fibrous layers of the superficial fascia are not very discrete in the cadaver. In some regions (e.g., palms), the superficial fascia is tightly bound to the investing fascia; in others (e.g., penis, eyelid), it is loosely bound.
2. ANTERIOR BODY WALL,
THORACIC CONTENTS: LUNGS AND HEART
OBJECTIVES RESOURCES
1. Muscles
a. Identify on the cadaver the basic a. Netter, Plates 175, 176, 183;
fiber directions of these muscles: Discussions 2-1, 2-2.
-external intercostals
-internal intercostals
-innermost intercostals
b. Discuss the blood and nerve supply to these b. Netter, Plate 238, 239.
body wall muscles.
2. Blood Vessels
a. Demonstrate these arteries on the cadaver: a. Netter, Plates 236, 238.
-internal thoracic artery
-anterior intercostal branches
b. Discuss anastomoses (collateral circulation) b. Discussion 2-3; Netter, Plates
relevant in this dissection: 234, 238.
-superior epigastric (continuation of int. thoracic)
(-inferior epigastric).
3. Review the components of the ventral rami 3. Discussion 2-4
of thoracic spinal nerves seen in this
dissection:
-general sensory
-somatomotor
-postganglionic sympathetic.
OBJECTIVES RESOURCES
4. Serous Membranes in the Thorax
a. Demonstrate on the cadaver the adult a. Netter, Plates 184-186.
relationships of the pleura including:
-costodiaphragmatic recesses
-costomediastinal recesses
-visceral vs. parietal (costal,
diaphragmatic and mediastinal) pleura
-pulmonary ligament
b. Identify phrenic, vagus and left recurrent b. Netter, Plates 182,195,
laryngeal nerves. 214,215,218,219.
c. Demonstrate on the cadaver the oblique and c.&d. Netter, Plate 203.
transverse sinuses within the pericardial
cavity.
d. Describe sites where visceral pleura /
pericardium reflect from the lungs / heart
to become continuous with the parietal
pleura / pericardium, respectively.
5. Anatomy of the Lungs
a. Identify lobes and fissures of right and left a. Netter, Plates 184-186.
lungs (oblique and horizontal fissures,
superior, middle and inferior lobes) and
appreciate how the fissures relate to
surface anatomy (ex., intercostal spaces).
b. Identify structures entering and b. Discussion 2-5;
leaving the lung at the hilus and Netter, Plate 187.
demonstrate examples of these
in the cadaver, specifically:
-pulmonary art. and vein
-primary bronchus
-bronchial art. and vein
c. Appreciate the role of the bronchial arteries
and their site of origin off the descending
aorta.
d. Define bronchopulmonary segment. d. Netter, Plates 188, 189;
Discussion 2-6.
e. Discuss the clinical significance of the e. Discussion 2-6.
bronchopulmonary segments.
OBJECTIVES RESOURCES
6. Anatomy of the Heart
a. Identify the right and a. Discussion 2-7; Netter,
left coronary arteries and the Plates 204-205.
following major branches:
-posterior interventricular
-marginal
-anterior interventricular
-circumflex.
b. Discuss implications of coronary collateral b. Discussion 2-7.
circulation.
c. Identify on cadaver heart the greater, middle c. Netter, Plates 204-205, 208.
and small cardiac veins and coronary sinus.
Find the opening of the coronary sinus in
the right atrium.
d. Explain possible significance of smallest d. Discussion 2-7.
cardiac veins.
e. Discuss vagal (parasympathetic) and
sympathetic innervation (cardiac plexus) of
the heart.
f. Explain the anatomy of the conducting f. Discussion 2-8; Netter,
system (the parts cannot be observed grossly Plate 213.
in the human heart):
-S-A node (location)
-A-V node (location)
- atrioventricular bundle
- Purkinje fibers
g. Identify on cadaver heart and describe g. Netter, Plates 208-211;
functions and/or significance of: Discussion 2-9.
-pectinate muscles -crista terminalis
-fossa ovalis -atrioventricular valves
-venae cavae -trabeculae carnae
-papillary muscles -chordae tendinae
-pulmonary veins -ligamentum arteriosum
-pulmonary valve -aortic valve
- openings for coronary arteries in aorta
7. Describe the structure and function of the
"skeleton" of the heart.
8. Summarize the transition from fetal to adult Discussion 2-9; Netter,
circulatory pattern. Plate 217.
DISSECTION
Part 1
First, REMOVE all remaining fat and fascial material from the surface of the anterior thorax so that the pectoralis muscle fibers can be clearly seen. A sharp scalpel and forceps are the best tools for this.
1. In preparation of removal of the anterior thorax, SEVER the proximal attachments of the pectoralis major and pectoralis minor muscles, then the serratus anterior muscle from the ribs and sternum. Have an atlas handy. Do this on both sides. As you reflect the pectoralis muscles be aware of their neurovascular bundles running along their deep surfaces so that they are not damaged. TAKE SPECIAL CARE WHEN CUTTING THE PECTORALIS MAJOR MUSCLE FROM THE CLAVICLE, WHICH YOU ONLY HAVE TO DO AT THIS POINT FOR A SHORT DISTANCE, i.e., UNTIL THE MUSCLE CAN BE REFLECTED AWAY FROM THE RIB CAGE. ITS NEUROVASCULAR BUNDLE IS EASY TO CUT IF YOU ARE NOT CAREFUL! You will find that after the initial severing of the proximal muscle attachment sites, the remainder of the pectoralis major can be bluntly separated from the ribs with your hands. Likewise, as you clean and prepare to reflect the serratus muscle (reflect this muscle again only far enough to allow adequate removal of the ribs for access to the thoracic cavity) be aware that its neurovascular bundle runs along the superficial aspect of this muscle. THESE MUSCLES WILL BE DISCUSSED IN A SUBSEQUENT LAB.
2. Note that the external intercostal muscles begin slightly lateral to the costochondral junction. Between the origin of the external intercostal muscle and the sternum, on one side only, carefully REMOVE one or two blocks of internal intercostal muscle. The intervening piece of cartilage rib may also be taken out to improve visibility (see figure). These cuts will expose the fairly large internal thoracic artery and vein, which parallel the edge of the sternum. WE WILL FOLLOW THESE VESSELS TO THE SUBCLAVIANS IN A LATER LAB.
Drawing
4. REMOVE the rib cage on either side of the sternum as two separate pieces. This will allow you to replace it when examining the relationship of the anterior thoracic wall to the anterior surface of the heart and lungs. While removing the ribs, be sure to PRY AWAY the underlying parietal pleura which lines the inner surface of the rib cage. Try to leave this membrane as perfect as possible, although holes will probably be made. Sometimes a block under the shoulder blades will allow the shoulders to droop, giving better access to the thorax. Be careful of the cut ends of ribs--they are very sharp. Try to demonstrate the external, internal and innermost intercostal muscles, and the intercostal arteries, veins and nerves associated with the rib cage you removed, although this neurovascular bundle will be more easily seen on the posterior thoracic wall. Note the location of the vessels and nerve relative to the rib. Now remove the sternum, again, carefully separating it from the underlying soft tissues. Since the clavicles have already been removed, do the best you can to carefully remove it from the manubrium to your inferior cut superior to the xiphoid process.
5. When the anterior rib cage and sternum are gone, you may find a mass of adipose tissue of variable size in the superior mediastinum. This often elongated, bilobed structure is the thymus gland. After examining it, remove it to expose deeper structures, such as the arch of the aorta and the left brachiocephalic vein.
6. On either side of the mediastinum, note that the two pleural sacs are now exposed. With a scissors, INCISE both sacs and lay back the flaps to show the lungs. Be sure to appreciate that the two pleural sacs are INDEPENDENT and NEVER connect medially even though they approach each other closely. PEEL BACK the mediastinal parietal pleura from the pericardial sac on both sides. While doing this, be sure to IDENTIFY both phrenic nerves that lie along, and are usually adherent to, the lateral sides of the pericardial sac. With a finger, FREE these nerves from their adherence to the pericardium, but leave them intact.
7. Now, with a scissors, OPEN the pericardial sac widely with a large "X" (see figure). Once again, avoid cutting the phrenic nerves. At this time, note that the bottom of the sac is adherent to the diaphragm and is actually a part of the tendinous area of the diaphragm. IDENTIFY THE OBLIQUE AND TRANSVERSE SINUSES.
8. BEFORE PROCEEDING WITH REMOVAL OF THE LUNGS, TAKE TIME TO STUDY THE RELATIONSHIPS BETWEEN THE HEART, LUNGS, GREAT VESSELS AND AIRWAYS. ALSO, IF THE NECK HAS ALREADY BEEN DISSECTED, NOTE THE CONTINUITY OF THESE VESSELS INTO THE NECK.
very careful not to cut the vagus nerve which runs just posterior to the hilus! TAKE OUT this lung. Repeat this procedure with the other lung.
10. Demonstrate the structures associated with the lungs as listed in the OBJECTIVES. In the thoracic cage, demonstrate the parietal (costal, diaphragmatic and mediastinal) pleura and the costodiaphragmatic and costomediastinal recesses.
11. On one lung, beginning at the hilus, STRIP AWAY the lung tissue with a forceps to expose the bronchi and vessels, as you see in the figure on the next page. You should show the bronchus and artery running together, whereas the darker pulmonary veins will have an independent course. Why?
Part 2
12. Before removing the heart, locate the left vagus nerve and its branch, the left recurrent laryngeal nerve as it wraps around the aortic arch. Also clean up the ligamentum arteriosum just anterior to the recurrent laryngeal nerve, between the left pulmonary artery and aortic arch. You will have to remove mediastinal pleura to find these structures so ask for help if you are having problems. Once you have located the nerve and ligament you should protect them as you begin to remove the heart. I would prefer to have you WAIT to find the right vagus until after you have followed the azygos vein in the next lab. The azygos is superficial to the right vagus during a portion of its route and can be damaged while in search for the nerve.
13. To remove the heart, please follow these instructions carefully! All cuts should be made close to the surface of the heart and therefore within the pericardial sac. First INSERT your fingers in the transverse sinus close to the heart. Now CUT the outflow vessels, namely the pulmonary trunk and ascending aorta just superior to your fingers. Next, cut the superior and inferior vena cavae close to the heart. Since both lungs have been removed, you should now be able to fairly easily pull out the heart, because the pulmonary veins have already been cut. The ligamentum arteriosum should still be intact and in the cadaver upon completion! Relocate it, the left vagus and the recurrent laryngeal nerve.
14. With the heart removed, take turns to carefully PICK AND STRIP AWAY the fat on the heart with forceps, or else vigorously but bluntly scrape it away with a scalpel handle or scissors. This action will expose the large coronary arteries and the larger branches of the cardiac veins. The arteries in particular are important to show well. Then demonstrate the structures associated with the heart as listed in the OBJECTIVES section of your notes.
15. To OPEN the right atrium, it is easiest to begin the cut at the superior vena cava and carry it through the inferior vena cava. Rather parallel to this cut, OPEN the right ventricle by starting in the pulmonary trunk. Refer to the figure on the next page. Then with a scalpel CUT a window in the wall of the left ventricle between the coronary arteries. The left atrium should also be opened by making a cut from one set of pulmonary veins to the other. The heart is now ready for inspection and study. You will first, however, need to carefully remove the clotted blood inside the chambers with your hands and with water. Again, demonstrate the internal structures of the heart as listed in the OBJECTIVES section.
Drawings
DISCUSSION
2-1 Deep Fascia
This term applies to all fascia deep to the subcutaneous tissue. Upon removal of all the subcutaneous tissue, one confronts a complete fascial investment as mentioned in Discussion 1-3. This is what is meant by the deep or investing fascia. Whatever is encountered--muscle, aponeurosis, bone, gland (e.g., parotid)--will be invested. In places this fascia is tough; in other places it is fairly delicate. Various regional names are applied, e.g., cervical investing fascia, fascia lata, etc. It blends with the periosteum where bone is immediately subcutaneous, such as on the anterior surface of the tibia, the sharp border of the ulna, the zygomatic process, clavicle, etc. These sites can be palpated. Intermuscular septa pass inward to the bones at other sites to subdivide muscles into groups. In some regions the underlying muscle is separated by a loose, areolar layer from the investing fascia.
The deeper layers of the deep fascia generally enclose individual muscles. Thus, each muscle will possess its own fascial compartment which restricts local bulging or protrusion. A weak spot or tear in this fascia may result in herniation of muscle tissue upon contraction. The fascia immediately enclosing a muscle is referred to as the epimysium. Fibrous tissue continuous with this investment surrounds muscle fascicles (groups of muscle fibers) and is referred to as perimysium. Continuous with this and ensheathing individual muscle fibers is the endomysium (not visible grossly). It is usually easy to separate individual muscles once the investing fascia is removed by simply running the fingers through the areolar tissue between their epimysia. In some situations this is not so easily accomplished, e.g., between internal abdominal oblique and transversus abdominis.
2-2 - Musculature
To avoid ambiguity, the three primary sorts of muscle are best referred to as smooth, cardiac or heart, and skeletal muscle. Each is specialized for a different role, although all are designed for active traction (pulling). For example, smooth muscle contracts with low speed and force, but with high energetic economy and range; it is virtually indefatigable. For these reasons it is the appropriate muscle for the wall of the gut and blood vessels, for example.
The heart obviously must continue to beat throughout life, and a rich blood supply to this organ is essential because the heart's muscle must never build up an oxygen debt.
Skeletal Muscle
On the average, about 40% of adult lean body weight is skeletal muscle, which is the primary heat-producing tissue in the body.
A false impression of muscle characteristics is presented by the embalmed cadaver with regards to color, texture, and pliability. In life, skeletal muscle at rest is remarkably unresisting and elastic (up to a certain limit), not tough and stiff. It is as much specialized for relaxation as for contraction. If this were not so, movement would require much more energy than it does.
Growth and Development
Many muscles migrate during development, dragging their nerve supply along. For example, the diaphragm is derived from upper cervical myotomes, but in the adult it is found in the lower thoracic region.
Muscle Attachments
Origin and insertion, are terms frequently used with the subject of skeletal muscles. However, these two terms, are often awkward and even inappropriate. As a rule, origin should be defined as the fixed end of a muscle, whereas the insertion should be identified as the movable end. At times, depending upon what the body is doing, origin and insertion for a given muscle may be reversed. To minimize possible confusion, anatomists generally use the term attachment, and simply qualify which attachment is meant, when necessary to do so: for example--medial/lateral attachments or proximal/distal.
Motor units
Each named muscle is actually composed of a number of motor units; a unit is defined as those muscle fibers innervated by one motor neuron. In large, coarse muscles, the ratio between the number of muscle fibers to one neuron could be over 1000 to one. With muscles under fine control (those that move the eyeball) the ratio could be less than 10 to 1.
2-3 - Collateral Circulation
Blood vessels in the body tend to join others of more or less the same dimension. Anastomotic connections of this kind comprise a collateral circulation. An example can be seen on this dissection--the internal thoracic artery and vein which lie directly deep to the cartilage ribs along the lateral edge of the sternum. Inferior to the ribs, a continuation of the vessels, ie., the deep superior epigastrics, anastomose with the deep inferior epigastrics, which lie on the deep surface of the rectus abdominis muscle. The internal thoracic artery, for instance, arises from the subclavian artery above and the deep inferior epigastric from the external iliac artery below. By means of the internal thoracic-deep inferior epigastric routing, blood can be shunted from one large vessel to the other, if necessary. Such collateral circulatory vessels can be valuable to surgery, allowing a tie off of them without really causing a problem, because blood can still reach the ligated ends from both directions.
2-4 - Ventral Rami of Spinal Nerves
These large branches of spinal nerves traverse the skeletal muscles of the thorax and abdomen, lying between the two deepest intercostals in the thorax and between the internal oblique and transversus abdominis in the abdomen. The ventral rami innervate the muscles they pass by and keep their independence at all times. Those entering the abdomen pass into the rectus muscle and then terminate as anterior cutaneous nerves which you dissected during the last session. Lateral cutaneous nerves, which you also found, are lateral sprigs of the same ventral rami. Because the ventral rami innervate the muscles, they will contain somatomotor fibers as well as general sensory and postganglionic sympathetic (both of which mainly go on to the skin).
2-5
Many organs within the body cavities have an indentation which defines the site where structures related to the function of the organ enter or leave. This site is called the hilus. If one considers the function of the organ concerned and the tissues comprising the organ, it is not difficult to generate a list of structures which would be essential to the economy of that organ. Some structures, such as lymphatics and networks of fine nerve bundles may be subtle at the gross level because they often do not reveal themselves to the aggressive dissector. A complete list of such structures at the hilus of the lung would include: bronchi, pulmonary arteries, pulmonary veins, bronchial arteries and veins, lymphatics (including hilar nodes) and branches of the pulmonary plexus of nerves. Each of these plays a role in the functioning of the lung and you are expected, in general, to understand what each does. It is of special interest to note that some aortic blood (oxygenated) must enter the lungs (via the bronchial vessels) to nourish the bronchial tree itself.
2-6
The air passages (trachea; primary, secondary, and tertiary bronchi; bronchioles) subdivide progressively and distribute throughout the lung, terminating in alveolar sacs. Pulmonary (and the small systemic bronchial) arteries likewise subdivide and run on the surface of or close to the air passages at all levels. Pulmonary (but not bronchial) veins run separately and are found in the connective tissue between adjacent segments. While the same pattern exists at all levels of calibre, the regions of lung aerated by tertiary (third-order) bronchi are designated bronchopulmonary segments. You are not expected to learn them in this course, but you should be aware of them. The pulmonary arterial branches are intrasegmental, while the corresponding veins are intersegmental. It should be clear that the veins receive tributaries from both segments at an interface.
In general, the surgeon often finds it convenient to remove one bronchopulmonary segment when the given disease process is restricted within it. By identifying and tying off the tertiary bronchus and corresponding pulmonary artery to that segment, the boundaries of the segment can be identified by the color change and the collapsed portion of lung (no air). The intersegmental veins traveling around the segment are identified, and only those tributaries draining the involved segment are ligated.
The living lung is flexible and elastic, unlike the lung of the cadaver. If the pleural space is opened to the air, the living lung collapses.
2-7 - Vasculature of the Heart
A knowledge of the distribution of major arteries will be assumed from your work in the laboratory. The best approach is to dissect the arteries as carefully as possible and learn by observation. Most are named by their distribution, and many arteries to large muscles, for example, can simply be called by the name of the muscle supplied.
The coronary arteries are of such extreme importance that a detailed understanding is expected. The left coronary with its anterior interventricular and circumflex branches and the right coronary with its marginal and posterior interventricular branches should be understood.
In the usual cases in the human, there is a balanced distribution between the two coronary arteries, i.e., the left coronary supplies the anterior portion of the interventricular septum, the left ventricle and the left atrium; the right coronary artery supplies the right ventricle, right atrium and the posterior portion of the interventricular septum. When variations do occur, we speak of a right or left dominant coronary artery. Such variations always occur on the back of the heart. When the right is dominant, it extends onto the back of the left ventricle assuming a supply to an area ordinarily supplied by the circumflex branch of the left coronary. When the left is dominant, the posterior interventricular is a branch of the circumflex artery of the left coronary.
Collateral connections between the coronary branches is still a topic of some dispute. Extensive literature exists on the subject, but most studies are conservative in their interpretations. In general, collateral circulation between these vessels is not well developed but develops to a variable extent following occlusions.
It is significant to realize that not all venous blood from the myocardium returns via the coronary sinus. There are anterior cardiac veins which empty directly into the right atrium. In addition, there is an alternative route, the smallest cardiac veins, which empty directly via small openings (not grossly visible) into the heart chambers. These small channels are unvalved and connect to the same capillary bed supplied by the coronary arteries. Extreme cases have been reported in which both major coronary arteries were occluded. Reverse flow from the heart chambers into these small veins plays an important role in maintaining a precarious existence for the heart muscle in these patients.
2-8
The conducting system of the heart cannot be seen satisfactorily at the gross level. The sinuatrial node (located in the anterior groove between the superior vena cava and the right atrium, at the superior edge of the crista terminalis) initiates the impulse. The wave of depolarization spreads through the atrial musculature to the atrioventricular node (located in the lower part of the interatrial septum between the opening of the coronary sinus and the tricuspid valve). From this node a bundle of modified cardiac muscle, the atrioventricular bundle, descends through the membranous portion of the interventricular septum where it divides into two bundles or crura, which lie deep to the endocardium on either side of the muscular I-V septum. The two crura end as Purkinje fibers which are in continuity with true cardiac muscle fibers at the apex of the heart.
It is important for the cardiac surgeon to know the location of the atrioventricular bundles, because in repair of I-V septal defects in the membranous portion, the conducting system can be damaged by improper placement of sutures.
2-9 - Fetal Circulation
Circulation of blood in the fetus differs significantly from the adult pattern. The placenta serves as a vital intermediary between the developing fetus and the mother and must receive a major blood supply. Oxygen and nutrients pass from the maternal vessels across the placental barrier to gain access to the fetal vessels. Likewise, various waste products leave the fetal capillaries to enter the maternal vessels. Thus, it is not essential that the digestive tract, lungs and kidneys of the fetus receive amounts of blood normally commensurate with their adult functions. An important consideration is that the fetal circulation must be adaptable to a sudden change to a quasi-adult pattern within minutes following birth.
There are several significant structures which function to distribute the blood properly in the fetus. These structures are adaptable to sudden changes following birth so that the transition to the adult pattern may occur. You may want to have Netter, Plate #217 handy to assist you in understanding the following discussion.
Except for the aorta itself, the umbilical arteries are the largest systemic vessels in the fetus. They represent the continuation of the internal iliac vessels and pass cranially to the umbilicus. They deliver blood to the placental capillary bed where exchange of materials occurs with the maternal tissues. Blood is returned to the fetus via a single umbilical vein which proceeds from the umbilicus cranially to the liver where the majority passes by way of the ductus venosus into the inferior vena cava bypassing the liver sinusoidal bed. Blood in the inferior vena cava enters the lower posterior portion of the right atrium and is directed through the foramen ovale into the left atrium. A smaller amount enters the right ventricle. Blood in the left atrium enters the left ventricle from which it is pumped on systole into the aortic arch. The three major vessels arising from the aortic arch (brachiocephalic, left common carotid and left subclavian) along with the coronary arteries which branch from the ascending aorta, receive the majority of this oxygenated blood. The blood returns via the superior vena cava to the right atrium where it is directed toward the right atrioventricular canal. Most of this blood enters the right ventricle and is pumped during systole to the pulmonary trunk. The major continuation of the pulmonary trunk is the ductus arteriosus which connects to the aortic arch just beyond the left subclavian artery. The poorly oxygenated blood from the ductus arteriosus is directed to the trunk and lower extremity. A major portion continues into the umbilical arteries for another cycle.
It is important to remember that the fetal lungs get a blood supply while the extensive capillary bed is developing. However, this capillary bed remains in a relatively collapsed state, because the lungs themselves are filled with incompressible amniotic fluid rather than compressible air.
Changes at birth. The significant event which occurs at birth is the first respiratory cycle. This single phenomenon relates to all of the subsequent changes. When the alveoli fill with air, the resulting air-liquid interface results in forces which open the lung capillary bed. This reduces the pulmonary blood pressure resulting in an increased flow through the pulmonary arteries. The blood is now oxygenated by the fetus and significant amounts are now returned via the pulmonary veins to the left atrium. The consequent increased pressure in the left atrium pushes against the flap of the foramen ovale restricting right-to-left flow. The fusion of the flap over the foramen ovale, forming the fossa ovalis, is usually complete by about 3 months after birth, although it is not uncommon to find a patent or partially patent foramen ovale in a cadaver. The ductus arteriosus, apparently kept open in fetal life by circulating prostaglandins, constricts (again, apparently) in response to a rise in oxygen tension, and in time (10 to 15 hours after birth) it becomes a fibrous cord--the ligamentum arteriosum. However, studies indicate that the ductus may remain patent in up to 65% of infants two weeks of age. Because the pressure is slightly greater in the aorta, such flow as does occur through the ductus would be from aorta to pulmonary vessels or the reverse of what occurs in the fetus. However, coughing or crying spells with resultant increased pulmonary pressure may produce flow in the opposite direction, shunting deoxygenated blood from the pulmonary vessels into the aorta. This explains the cyanosis observed in crying infants. As another aside, in premature infants, prostaglandin inhibitors such as indomethacin are sometimes administered to constrict the ductus.
At birth the placenta contains about 100 cc of blood or roughly one-third of the total blood volume. This is about equal to the increase in blood volume passing to the lungs following the first respiratory cycle. The presence of oxygenated blood in the umbilical arteries causes a reflex contraction of their smooth muscle walls. Within minutes they are tightly constricted. The umbilical arteries remain as fibrous remnants--the medial umbilical ligaments. Uterine contractions force blood from the placenta so that within 5-10 minutes the 100 cc blood has been returned to the fetus. Then the umbilical vein collapses from the lack of blood and in time becomes the round ligament of the liver. The ductus venosus constricts in a sphincter-like action (apparently vagus nerve control) and in time becomes the ligamentum venosum. It remains patent for a time, however, and transfusions in the newborn are frequently given through the stub of the umbilical vein.
SUMMARY
1) The most significant event in the transition to adult circulation is the opening of the pulmonary capillary bed.
2) Significant fetal structures which should be understood are the umbilical arteries, umbilical vein, ductus venosus, foramen ovale, and ductus arteriosus. Their adult counterparts are all identifiable in the cadaver!
3. POSTERIOR MEDIASTINUM AND THORACIC WALL
OBJECTIVES RESOURCES
1. Autonomic Nervous System
a. Review general organization and functions 1a.-e. Discussions 3-1 - 3-3;
of autonomic system and identify: Netter, Plates 153, 218-219.
sympathetic trunk, communicating rami,
splanchnic nerves, and both vagus nerves.
b. Understand location of presynaptic
(preganglionic) and postsynaptic
(postganglionic) sympathetic and
parasympathetic nerve cell bodies.
c. Trace autonomic pathways from
presynaptic nerve cell bodies to ultimate
innervation of tissue within thoracic cavity
and thoracic body wall. Identify the
esophageal plexus and discuss the
components of the cardiac and pulmonary
plexus.
d. Trace sensory fibers from viscera to
location of nerve cell bodies.
e. State the roles played by parasympathetic
and sympathetic divisions of the ANS.
2. Lymphatics
a. Demonstrate the thoracic duct in the cadaver. a. Netter, Plate 227.
b. Consider lymphatic system in general and b. Discussion 1-1.
explain factors which aid in the return of
lymph to the venous system.
3. Venous Drainage of Thorax
a. Consider the venous system of the thorax a. Netter, Plate 226.
and abdomen in general. Identify:
-azygos
-hemiazygos
-accessory hemiazygos (if your cadaver has one)
-posterior intercostal veins
-esophageal veins.
b. Describe collateral
connections of azygos system.
4. Thoracic aorta
Identify: 4. Netter, Plate 225.
-posterior intercostal arteries
-esophageal arteries.
DISSECTION
1. BLUNTLY SEPARATE the empty pericardial sac from the underlying esophagus being careful to leave the fibrous-looking esophageal autonomic nerve plexus on the esophageal wall. This is best done with the fingers. Next, while preserving the phrenic nerves, make a horizontal cut through the now loosened sac as illustrated in the figure and either remove it or simply reflect it such that the esophagus and other structures within the posterior mediastinum are handy for dissection. BE CAREFUL of the cut ends of the ribs, as they are very sharp and lacerate you easily. It is wise to fold a paper towel over them. Once again, a block under the upper back often allows the shoulders to droop, giving better access to the posterior thoracic wall on this dissection.
2. With forceps, STRIP OFF the parietal pleura from the posterior thoracic wall. This is often most easily accomplished if you start laterally at the cut edge of the ribs and work medially. The important point is to be sure to remove the mediastinal pleura from both sides of the esophagus, descending aorta and vertebral bodies. Identify each of these structures as you clean the pleura from their surfaces. Identify the azygos vein and follow it to where it joins the superior vena cava. DO NOT destroy the esophageal nerve plexus around the esophagus. Follow the plexus up to the left and right vagus nerves. You identified the left vagus nerve in the last lab. Now be sure to find the right vagus nerve as it travels along the right side of the trachea.
3. Now bluntly (the handle of your forceps works well) SCRAPE AWAY fat and fascia to expose the sympathetic trunk, the thoracic splanchnic nerves MEDIAL to the trunk (usually several and continuing caudally to penetrate the diaphragm) and the communicating rami (pre- and postganglionic) LATERAL to the trunk that unite the sympathetic trunk and the ventral rami of the thoracic spinal nerves. Identify these ventral rami, which are more specifically referred to as the intercostal nerves in this location.
4. Gently DEFLECT the esophagus from the posterior body wall just far enough to reveal its vasculature. Identify at least one or two esophageal arteries and veins and follow them to their source / destination, respectively. Having done this, with esophagus still deflected anteriorly, carefully remove the fat located posterior to the esophagus along the right side of the aorta to find the thoracic lymphatic duct. The duct is thin-walled with little strength, but generally can be easily found between the azygos vein to its right and the aorta to its left.
5. To find the variable hemiazygos and accessory hemiazygos veins on the left side of the body, deflect the esophagus and aorta to the right. If these veins are not immediately apparent to you, you can either follow the posterior intercostal veins along the left thoracic wall to the azygos system, or, alternatively, you may be able to find a connecting vein between the azygos and hemiazygos traveling across the anterior aspect of the vertebral bodies.
Drawings
DISCUSSION
3-1 - The Autonomic Nervous System (ANS)
You have already considered the sensory and somatic motor components of the peripheral nervous system in Dissection 1, and it is now time to consider the organization of the autonomic nervous system.
The autonomic nervous system is purely motor in function, but--unlike the somatic motor system which controls skeletal muscle--it innervates smooth muscle, cardiac muscle and glands. Anatomically, the most important distinguishing feature of the autonomic system is that two neurons (as opposed to one for the somatic motor system) are necessary to transmit an impulse from the central nervous system (CNS) to its target. The first neuron has its cell body in the CNS (more specifically in a motor nerve nucleus) and is called the preganglionic or presynaptic neuron. Its axon leaves the CNS and synapses with a second neuron whose cell body lies in an autonomic ganglion. This second postganglionic or postsynaptic neuron in turn sends its axon to the target muscle tissue.
The ANS has two divisions: the sympathetic system and parasympathetic system. To consider the sympathetic system first, the preganglionic neurons of the sympathetic system lie in motor nuclei in the lateral horn of the spinal cord from levels T1 (first thoracic) to L2 (second lumbar) and hence are also given the name thoracolumbar. The axons of these lateral horn neurons leave the spinal cord via the ventral roots, enter the sympathetic trunk via communicating rami, and terminate either in the ganglia of the sympathetic trunk or in a collateral (or prevertebral) ganglion. The sympathetic trunks are paired chains of autonomic ganglia, one on each side of the entire vertebral column from the first cervical to lowest sacral levels. Since the presynaptic neurons are contained only in the spinal cord from T1-L2, ganglia in cervical, lower lumbar and sacral regions are supplied by presynaptic fibers which must travel up or down in the sympathetic trunks to end in a ganglion above or below this level. Furthermore, preganglionic fibers (from T1-L2) do not necessarily have to synapse in the ganglion at the level of entry. The postsynaptic neurons in the chain ganglia then send their axons into the spinal nerves; and because the sympathetic trunks extend the entire length of the vertebral canal, every spinal nerve contains postsynaptic sympathetic fibers which travel with the spinal nerves to the neck, body wall and limbs, there innervating the blood vessels, smooth muscle, and sweat glands of the skin. [Note that because the sympathetic trunk does not extend into the head, postganglionic fibers from neurons in the highest (superior) cervical ganglion reach the head by following arteries.] A final possibility for some of the presynaptic fibers is to pass through the sympathetic trunk without synapsing. These preganglionic fibers form splanchnic nerves which end in collateral (prevertebral) ganglia located around the major branches of the abdominal aorta. The postsynaptic neurons in the collateral ganglia send their axons along blood vessels to the smooth muscle and glands of the viscera. Their main function is to innervate the smooth muscle of the blood vessels (i.e., vascular smooth muscle).
The parasympathetic division of the ANS is also known as the craniosacral division, because its preganglionic cell bodies belong to motor nuclei (in the brain) of cranial nerves III, VII, IX and X or else are part of the motor nuclei in the spinal cord at sacral levels 2, 3 and 4. Thus, the preganglionic axons leave the CNS as a component of a cranial nerve or as part of the ventral root of a sacral spinal nerve. As part of the ANS, these axons must also synapse in a ganglion before innervating the target tissue. However, the ganglia of the parasympathetic system are different in several respects from the sympathetic ganglia, i.e., they are located very close to or even within the walls of the organs that they innervate; they are widely scattered (unlike the regular chains of the sympathetic system); and they are usually small (even microscopic) in size, in contrast to the large, more easily identifiable ganglia of the sympathetic system. Because fewer postganglionic neurons are involved, the control exerted by the parasympathetic system is much more precise. Each preganglionic neuron synapses with only one or two postsynaptic neurons in contrast to a pre- to post-ratio in the sympathetic division of about 1 to 20. It should be apparent that the parasympathetic system, because it is limited to certain cranial and sacral nerves, has its distribution only to certain structures (primarily glands) in the head, and to the viscera of the trunk, in contrast to the sympathetic system which sends fibers to all parts of the body.
Functionally, the sympathetic and parasympathetic systems have contrasting roles. The sympathetic is an emergency system preparing the body for fight or flight, whereas the parasympathetic is a homeostatic system preserving the orderly functions of the body (rest and digest). Thus, the sympathetic system would speed up the heartbeat, dilate the pupil (to provide a wider field of vision), constrict blood vessels to the skin and gut (to increase blood supply to skeletal muscles), and slow down peristalsis in the gut. In contrast, the parasympathetic system would constrict the pupil (to protect the retina), decrease the heart rate, and increase peristalsis. However, it should not be concluded that every organ has a dual innervation. For example, blood vessels have only a sympathetic innervation and are dilated passively by pressure of the blood or possibly by vasodilator fibers which are part of the sympathetic system. In cases where both systems supply the same organ, there is coordination of activity rather than competition. For example, at rest, elimination of parasympathetic innervation of the heart increases heart rate, but eliminating sympathetic innervation produces no immediate change. This shows that the normal parasympathetic function is to maintain the activity of the heart at the lowest efficient level. In an emergency (i.e., sudden activity), the sympathetic system takes over and the parasympathetic system ceases to control the heart. This example also shows that cardiac muscle has a high degree of autonomy (this is also true of most smooth muscle), and in fact the heart will continue to beat--albeit more rapidly and strongly than normal--in the absence of any nerve stimulation.
3-2 - Sympathetic Trunks
a) The paired sympathetic trunks extend from the base of the skull to the coccyx. The trunks consist of a series of ganglia (groups of nerve cell bodies) connected by nerve fibers (axons). These fibers are primarily preganglionic autonomic axons that are ascending or descending within the trunk. There may also be some afferent (sensory) fibers coming from viscera to the CNS. (See Discussion 3-3.)
b) Communicating rami may be either preganglionic (white) or postganglionic (gray) depending on whether the fibers are myelinated or not.
Preganglionic rami are composed of axons whose corresponding cell bodies are located in the lateral horn of the spinal cord from T1 to L2. Their axons traverse the appropriate ventral roots and leave the spinal nerves as white rami to enter the sympathetic trunk. Sensory fibers entering the spinal cord from the viscera also traverse this communicating ramus.
Postganglionic rami are composed of axons whose cell bodies lie in the sympathetic chain ganglia and which are joining up with spinal nerves. Every spinal nerve gets a gray ramus, and distributes the fibers along with its own to the periphery.
c) Autonomic plexuses. An autonomic nerve plexus is simply a mixture of pre- and postganglionic nerve fibers from which fibers may sort themselves on their way to a target organ. Nerve fibers may pass through a plexus without synapsing in it although some plexuses may contain small ganglia. A nerve plexus is often named for an organ near which it lies. As an example, the cardiac plexus receives sympathetic fibers from the sympathetic trunk as well as parasympathetic ones from the vagus nerve. The sympathetic fibers are already postganglionic (cells of origin in the cervical and thoracic chain ganglia), but the vagal parasympathetic fibers are preganglionic, synapsing in microscopic cardiac ganglia located in the plexus and within the walls of the heart. Moreover, as described in Discussion 3-3, a plexus may contain sensory fibers coming from an organ.
3-3 - Visceral Afferents
Thus far we have considered only efferent (motor) fibers to the viscera. However, it is clear that there are afferent (sensory) fibers from the viscera to the CNS. Although such fibers may return by way of peripheral autonomic pathways, these sensory components are not part of the autonomic system which is, by definition, a motor system.
The nerve cell bodies of afferent fibers from the viscera may lie in either the dorsal root ganglia or in sensory ganglia belonging to cranial nerves, particularly the vagus nerve. The central processes associated with the spinal cord pass in corresponding dorsal roots to the CNS. Those processes associated with the cranial nerves travel from sensory ganglia to nuclei in the brainstem. Their peripheral processes are distributed with the pre- and postganglionic fibers of the parasympathetic or sympathetic systems. They are not interrupted in autonomic ganglia, however, but pass right through. Their receptors are located in the walls of the viscera and in the walls of blood vessels. Afferent impulses conducted along these neurons can initiate visceral reflexes, but do not usually reach the level of consciousness. They convey visceral sensations such as hunger, nausea, sexual sensation, rectal and bladder distension or various degrees of pain.
The vagus, or tenth cranial nerve, has a large visceral afferent component. All of the cells of origin lie in the sensory ganglia of the vagus, and their peripheral processes have a wide distribution, resulting in poorly localized sensations. Such terminals can be found in the heart, walls of the great vessels, esophagus, the lungs, stomach, intestines and kidney, for example. The pelvic viscera send afferent impulses to the CNS by way of the pelvic splanchnic nerves. The cells of origin of these sensory fibers which may, for example, terminate as stretch receptors in the bladder and cervix, are located in the dorsal root ganglia of sacral nerves S2, 3, and 4.
In general, afferent fibers which travel with pre- and postganglionic fibers of the sympathetic system have a sequential arrangement. They end in the same spinal cord segments as the preganglionic fibers of the efferent autonomic pathway to the region or organ, resulting in more discretely localized sensations. Afferent (sensory) fibers to thoracic and upper lumbar spinal segments conduct mostly pain impulses from such organs as the heart, esophagus, stomach, intestines, kidney, ureter and gall bladder. Their cell bodies are located in dorsal root ganglia at appropriate thoracic and lumbar levels.
As mentioned above, visceral pain fibers, which deserve special attention, also follow these peripheral pathways. Viscera are insensitive to cutting, crushing or burning, but excessive tension or contraction of smooth muscle produces visceral pain, as in the case of abdominal pain due to excessive intestinal contractions. Visceral pain which is poorly localized and tends to be dull or heavy travels with visceral afferent fibers traveling with the parasympathetic system. Pain fibers from the heart which carry pain that is sharp and well localized enter the spinal cord through the 1st to 4th thoracic spinal nerves. These pain fibers are believed to travel exclusively with the sympathetic components of nerves to the heart.
4. SUPERFICIAL AND INTRINSIC MUSCLES OF THE BACK
OBJECTIVES RESOURCES
1. Vertebral column and intrinsic
back muscles
a. Discuss movements allowed at
the atlanto-occipital, atlanto-
axial joints and other cervical
intervertebral joints.
b. Discuss movements allowed by
the thoracic vertebral column and
the lumbar vertebral column.
d. Explain how the structure of
the intervertebral disks
contributes to movements of
the vertebral column.
e. Identify the following on a e. Netter, Plates
typical vertebra: 143, 144.
- spinous process
- lamina These form the
- pedicle neural arch.
- transverse process
- body
- superior & inferior
articular processes
- vertebral foramen (canal)
- superior & inferior These form the
vertebral notches intervertebral foramen.
f. Identify: f. Netter, Plates
in the cervical and 160, 161, 162.
and cranial regions:
splenius capitis, semispinalis
capitis;
in the thoracic region:
iliocostalis, longissimus,
and spinalis columns and the
transversospinal muscles;
in the lumbar region:
multifidus.
g. Understand the general actions g. Discussion 4-1.
of each muscle group.
h. Consider the innervation and vascular h. Netter, Plates 158, 166, 179.
supply to these intrinsic back muscles.
DISSECTION
1. If it has not already been done, skin the posterior aspect of the neck to reveal the superior attachment site of the trapezius muscle. If the head and neck have already been dissected, there is a the midline cut through the skin and posterior neck musculature. Therefore, on these bodies it may be easiest to skin this region in a cephalic direction. Likewise, in the lower back, be sure that the skin is removed to expose the iliac crests and the sacrum, and the caudal portion of the latissimus dorsi and its aponeurosis.
2. Before proceeding, locate 2 clinically important triangles. The first is the triangle of auscultation, that space bounded by the trapezius muscle, the latissimus dorsi and the vertebral border of the scapula. This triangle is used to auscultate the thoracic cavity. The second triangle, the lumbar triangle, is bounded by the lower lateral border of the latissimus dorsi, the posterior edge of the external abdominal oblique muscle and the ilium. This triangle is a point of weakness in the posterior abdominal wall where herniations can occur.
3. Now separate the trapezius in a medial to lateral direction from the vertebral spines and underlying musculature. It should remain attached to the lateral aspects of the clavicle and spine of the scapula. As you continue to flap back the trapezius laterally, find its innervation, the spinal accessory nerve (CN XI) and it vascular supply, the superficial branch of the transverse cervical artery, entering the deep surface of this muscle. We will follow this artery back to its source (the subclavian artery) in a later lab.
4. On both sides CUT the attachments of the latissimus dorsi from the vertebral spines, scapula and ilium and reflect this muscle as well (only its attachment to the humerus should remain intact at this point). The innervation and vascular supply to the lattisimus will be more easily seen in a later lab. Deep to the latissimus dorsi muscles will be the thin serratus posterior inferior muscles. CUT these muscles from the vertebral spines and reflect them.
5. Now, SEVER the two rhomboid muscles from the vertebral spines and lay them back. As these muscles are reflected, locate their innervation, the dorsal scapular nerve, and blood supply, the deep branch of the transverse cervical artery (if there is no deep branch, the dorsal scapular artery replaces it). Deep to the rhomboids will be the thin serratus posterior superior muscles. CUT these muscles from the vertebral spines and reflect them as well. Finally, locate the levator scapulae muscle and leave both attachment sites intact. We will discuss these superficial muscles of the back in a subsequent lab, but pay attention to their sites of attachment as you reflect them now.
6. The intrinsic back muscle mass is now exposed. Separate the splenius capitis muscle cleanly from the underlying semispinalis capitis muscle BEING CAREFUL to preserve the occipital artery (a branch of the external carotid artery) and greater occipital nerve (the dorsal ramus of C2, sensory to the back of the head).
7. Using an atlas for orientation, BLUNTLY SEPARATE with your fingers the three chains of the erector spinae muscles: iliocostalis (most lateral), longissimus (middle), and the largely tendinous spinalis (medial and against the vertebral spines). The latter group is usually restricted to the thoracic portion of the vertebral column.
8. Next, on one side, in the lower lumbar region make a vertical midline cut through the erector spinae tendon and bluntly reflect it laterally, to reveal the multifidus muscle lying along the laminae of the vertebrae. In the middle to lower thoracic region, cut away erector spinae muscle fibers until you can identify a transverse process. Now remove all muscle fibers
Drawings
from the lamina associated with that transverse process and find and name the various transversospinal muscles, following them from transverse to more superior spinous
processes, with the shortest ones (rotators, long and short) being the deepest. This can be quite difficult so ask for assistance if necessary.
DISCUSSION
4-1
The center of gravity for the trunk is anterior to the vertebral column so that muscular effort is required to maintain erect posture. The muscles which accomplish this are called "the intrinsic muscles of the back". Their function is to extend the head and vertebral column and to contribute to movements such as lateral bending and rotation of the vertebral column. Consider the semispinalis capitis as the most significant muscle in holding the head. The huge mass of muscle in the lumbar region, representing the origin of the erector spinae muscles, or superficial group of intrinsic back muscles, is most significant in holding the spinal column erect. Likewise, the deeper group of muscles, the transversospinae muscles, act to rotate the vertebral column.
5. VERTEBRAL COLUMN, SPINAL MENINGES and SPINAL CORD
OBJECTIVES RESOURCES
1. Vertebral column
a. Identify the locations of the a. Netter, Plates 146,
ligamentum flavum and the 147; Discussion 1-1.
anterior and posterior longitudinal
ligaments on the skeleton.
b. Understand the roles of the
annulus fibrosus and the
nucleus pulposus of an
intervertebral disk.
c. Locate the weakest part of the
intervertebral disk and
explain the consequences of
herniation in various parts of
the vertebral column.
2. Spinal meninges
a. Identify the spinal dura, a. Netter, Plates 155.
arachnoid and pia on the
cadaver.
b. Define the spinal epidural, b. Discussion 5-1.
subdural and subarachnoid
spaces and list their
contents.
c. Identify the following meningeal c. Discussion 5-1.
structures related to the spinal
cord:
- dural sac
- denticulate ligament / denticulations
- filum terminale
3. Spinal cord
a. Understand the significance
(both anatomical and clinical)
of the disparity in length of
the spinal cord vs. the
vertebral column.
b. Understand the significance of
the cervical and lumbar
enlargements of the spinal cord.
DISSECTION
1. With a scalpel sever all muscles between the transverse and spinous processes of the vertebrae, and associated with the sacrum on both sides. Now with a blunt instrument such as a chisel or a scalpel handle remove these muscles right down to the bone by scraping from spinous to transverse processes, leaving the laminae of the vertebral column (including the sacrum) bare.
2. With an autopsy or hand saw, cut a longitudinal groove in the vertebral laminae and the sacrum on both sides of the vertebral column from the upper thoracic region to the sacrum. Begin these grooves about half way between the spinous processes and the transverse processes. Aim your cut slightly medially toward the vertebral canal but do not cut through the entire thickness of the laminae or you may damage the underlying nerve roots. Refer to an articulated skeleton for guidance.
3. Complete the break on each side with a chisel and hammer, and, using the chisel as a lever, pry off the now loosened spinous processes and the posterior portion of the sacrum to expose the tough dura mater--the outermost meningeal membrane around the spinal cord. Try to identify the ligamentum flavum between adjacent vertebrae that you have just removed from the posterior aspect of the vertebral canal.
4. The dural sac should now be exposed. Open the length of the dural sac with a scissors. Extend this cut as far inferiorly as possible. Lay back the dural flaps to see the thin arachnoid mater collapsed against the spinal cord. Break this flimsy arachnoid layer with a probe to show the denticulate ligaments, which are the two lateral reflections of the pia mater, one on either side of the cord, and their denticulations which extend to the dura laterally. Identify also spinal rootlets (dorsal and ventral), the spinal cord, and the conus medullaris and cauda equina in the lumbar region of the spinal canal. The cauda equina is the collective name for the lower lumbar and sacral spinal nerve rootlets. Where are the dorsal root ganglia associated with these rootlets located? In the center of the cauda equina, find a white connective tissue strand
representing the filum terminale, the inferior extension of the pia mater from the tip of the conus medullaris. To what does it attach inferiorly? Be sure you know the vertebral levels at which it begins and ends.5. In the thoracic region, with a scalpel and forceps, carefully remove muscle tissue until you have dissected out two neurovascular bundles running in two adjacent intercostal spaces. Then with a rib cutter cut the two adjacent and one intermediate ribs about two inches from their site of articulation with the vertebrae. Now, using the ribs as a lever, bend them towards the midline in an attempt to separate them from the vertebral column and remove them. If necessary, use a rib cutter to complete the removal of the adjacent thoracic vertebral material to expose the dural sleeve around the spinal roots forming the spinal nerves associated with the intercostal nerves you have cleaned. Find also the swollen dorsal root ganglion. Distal to the dorsal root ganglion, identify both ventral and dorsal rami of the spinal nerve. Also, try to identify the two strands of the sympathetic communicating rami that join the spinal nerve to the sympathetic trunk. If necessary, remove more bone to show these rami more clearly. Be sure you understand what travels in these communicating rami!
Drawings
DISCUSSION
5-1
The vertebral canal is lined by periosteum and ligaments. The periosteum covers bony surfaces. The ligamentum flavum, which occupies the interlaminar spaces of the posterolateral wall of the vertebral canal, is distinguished by its yellow elastic tissue. This ligament deserves special note because elastic ligaments are somewhat unusual. Consider its role in movements of the vertebral column. The posterior longitudinal ligament lies along the posterior aspect of the vertebral body, which is also the anterior wall of the vertebral canal. It is narrow as it crosses the posterior surfaces of the vertebral bodies but flares out to blend with the annulus fibrosus of the intervertebral disk.
The meninges are the connective tissue coverings of the central nervous system. There are three: the outermost dura mater ("tough mother"), the intermediate arachnoid mater, and the pia mater ("tender mother") which intimately covers the brain and spinal cord. The arachnoid mater is a delicate, continuous membrane that lines the dura. However, it is also continuous with the pia mater by hundreds of delicate fibers called arachnoid trabeculae. It is because of this web-like appearance that this layer received the name arachnoid ("spider-like"). The pia mater, on the other hand, covers the spinal cord like a skin. It is a vascular connective tissue that differs in the spinal and cranial regions. Over the brain it is a delicate layer whereas the pia mater covering of the spinal cord is substantially thicker and gives rise to two denticulate ligaments, one on either side of the spinal cord. These are scalloped structures which anchor the spinal cord laterally to the dura mater by 26 pairs of tooth-like reflections of the pia called denticulations. These ligaments and their denticulations are located between the ventral and dorsal nerve rootlets. The filum terminale, a continuation of the pia mater, extends from the end of the spinal cord at the level of the second lumbar vertebra to the termination of the dural sac at the second sacral vertebra.
When the laminae of the vertebral canal are removed, the meninges and the meningeal spaces can be demonstrated. The meningeal spaces include the epidural space between the spinal dura and the vertebral canal, the subdural space between the dura and arachnoid and the subarachnoid space between the arachnoid and pia mater. The epidural space contains a plexus of thin-walled veins, loose connective tissue and fat. This space is essential for movement between the spinal dura and the vertebral column. The subdural space is a shallow, uniform space because the arachnoid lines the dura. It contains a thin layer of fluid. The subarachnoid space is a more substantial space filled with a clear, aqueous fluid, the cerebrospinal fluid (CSF). The subarachnoid space contains approximately 150-200 ml of CSF which is secreted by the choroid plexuses and ependymal linings of the ventricles. An appreciable amount of CSF is exchanged daily (about 500 ml) but it is misleading to state that CSF circulates. It is more appropriate to consider that it is produced under a secretory pressure and that it seeps its way like the flow through a swamp to its destination. CSF is frequently removed for diagnostic tests, usually from the lumbar subarachnoid space (lumbar puncture) below the termination of the spinal cord.
6. SUPERFICIAL DISSECTION OF THE UPPER EXTREMITY and DISSECTION OF THE AXILLARY FOSSA
OBJECTIVES RESOURCES
1. Limb compartments and their
development
a. Define the terms preaxial and postaxial a. Discussion 6-1.
as they relate to the limbs.
b. Define anterior and posterior
compartments in the limbs.
2. Cutaneous Nerves
a. Identify on the cadaver the a. Netter, Plates 448-450;
lateral and medial antebrachial Discussion 6-2.
cutaneous nerves of the forearm.
b. Define dermatome and explain why b. Discussion 6-3;
the distribution of cutaneous nerves For chart, see Netter Plates
in the limbs DOES NOT correspond 150,450, 451.
to the dermatome pattern.
3. Veins
Demonstrate on the cadaver the Netter, Plates 448, 449.
basilic and cephalic veins in
the upper limb.
4. Identify on a skeleton all the Netter, Plates 391-393, 409,
bones of the upper limb. 422-423,423; Discussion 6-4.
5. Axilla
Name areas from which lymph Netter, Plate 169;
drains to axillary nodes. Review Discussion 6-5.
lymphatic drainage of the mammary
gland.
6. Brachial Plexus
a. Identify on the cadaver the a-c. Netter, Plates 400-401.
roots, trunks, divisions, cords and
five terminal branches (axillary, radial,
ulnar, median, and musculo-
cutaneous). Identify the phrenic
nerve.
OBJECTIVES RESOURCES
6b. Know the muscles (by groups where
applicable) and regions of the skin
innervated by the motor and sensory
components, respectively, of each of
the 5 major branches of the brachial
plexus.
c. Identify the anterior and posterior c. Discussion 6-6.
division nerves of the brachial plexus.
d. Appreciate the relationships of the d. Netter, Plates 25, 28.
anterior, (and middle and posterior)
scalene muscles to the brachial plexus
and the phrenic nerve.
7. Arteries associated with the subclavian
artery
Locate on the cadaver the: Netter Plates 28, 68 and 69.
-internal thoracic artery
-transverse cervical and suprascapular
branches of the thyrocervical trunk.
8. Arteries associated with the axillary fossa
a. Locate on the cadaver the a. Netter, Plate 398.
following branches of the
axillary artery and identify
the regions supplied by each:
- highest (supreme) thoracic
- thoracoacromial
- lateral thoracic
- subscapular and its branches:
circumflex scapular and thoracodorsal
- anterior and posterior humeral circumflex.
b. Trace one significant collateral b. Netter, Plate 398;
route from the subclavian to the Discussion 6-7.
third part of the axillary.
DISSECTION
Drawings have not included with the dissection instructions for the upper extremity. You should use your atlas frequently during these dissections. In most cases, the relevant figures in Netter are cited in the dissection instructions.
1. Skin both upper limbs and preserve only those subcutaneous nerves and vessels mentioned below. Removal of the skin should be carried out in a rapid fashion. The dissection entails making parallel incisions through the skin and underlying superficial fascia along the length of the upper extremities to the wrist to isolate strips of skin 2-3" wide Try not to cut through the investing fascia covering the muscles.
After longitudinal incisions have been made, cut a small slit or hole in the proximal portion of the skin strip large enough to insert one finger so the strip can be pulled from the limb. Try to start a plane of separation so that as much fat is removed with the skin as possible. This procedure does not generally leave the entire course of the cutaneous nerves and vessels totally intact, since they are located within the superficial fascia, but does leave enough for reconstruction of the patterns of cutaneous innervation and venous drainage with the aid of an atlas.
2. In the upper extremity, the cephalic and basilic veins should be dissected. Two nerves, the lateral and medial antebrachial cutaneous nerves, follow these veins and are to be displayed as examples of cutaneous innervation (Netter, Plates 448, 449, 450, 452). The relationship between dermatomes and cutaneous nerves should be understood and the significance of the dermatome pattern in the extremities considered. Both sides should be dissected.
3. The pectoralis major and minor muscles have already been reflected from their thoracic wall attachments so that the axillary fossa is already partially exposed. Reconstruct the muscular walls of the axillary fossa. Observe the anterior, posterior, medial and lateral walls of the fossa using Netter Plates 399-400 as a guide.
4. On both sides find 2 of the major branches of the subclavian artery; the internal thoracic which you have already observed, and the transverse cervical, which you have also already seen associated with the trapezius and rhomboid muscles, and suprascapular branches of the thyrocervical trunk. Time permitting, feel free to follow the other branches. Refer to Netter Plates 28, 68 or 69.
5. Find the axillary vein (if you are having trouble, try following back either of the 2 cutaneous veins you dissected). This vein, along with the axillary artery and the proximal portion of the brachial plexus, lies within the neurovascular axillary sheath. Refer to Netter, Plates 169, 175, 399. The vein lies most medial (inferior) in the axilla. After identifying the vein, it and its branches can be removed. This is a good time to try to locate examples of axillary lymph nodes associated with this vein (Netter, Plate 169).
scalene muscle’s attachment from the first rib and reflect this muscle. Display and identify the branches of the axillary artery. The following branches of the axillary artery should be identified (bolded branches only): (Netter, Plate 398)
- highest (supreme) thoracic
- thoracoacromial (it has 4 branches but only the pectoral branch is usually intact for you
to identify)
- lateral thoracic (which travels near the long thoracic nerve if it originates from the
axillary artery but it more often than not originates from the thoracodorsal artery)
- subscapular and its branches:
circumflex scapular
thoracodorsal (which accompanies the thoracodorsal nerve)
- anterior and posterior humeral circumflex (the latter of which follows the axillary nerve and may branch off the subscapular artery).
DISCUSSION
6-1 - Pre- and Postaxial
These terms are not to be confused with anterior and posterior. The limb buds appear as flattened elevations from the ventrolateral aspects of the trunk. The paddle-shaped buds have a distinct upper or cranial margin and a lower or caudal margin that meet at the thickened apical ectodermal ridge. These margins of the developing buds represent, respectively, the pre- and postaxial borders. With the adult upper extremity in the anatomical position, the preaxial border runs from the tip of the shoulder to the thumb. The postaxial border runs from the base of the axilla to the little finger. A plane that runs from the preaxial border to the postaxial border would bisect the limb into anterior and posterior compartments. Anterior muscle groups which occupy the anterior compartment function as flexors (and are innervated by anterior division nerves) whereas posterior compartment muscles function as extensors (and are innervated by posterior division nerves).
6-2 - Cutaneous Nerves and Veins
You are asked to identify the 2 cutaneous nerves indicated as examples from among many. These nerves distribute along prominent subcutaneous veins as follows: the lateral antebrachial cutaneous nerve accompanies the cephalic vein; the medial antebrachial cutaneous nerve accompanies the basilic vein. The parent trunks of these nerves will be observed in our study of the brachial plexus.
6-3 - Dermatomes and Cutaneous Nerves
As discussed previously, a dermatome is the entire area of skin receiving sensory innervation from a single spinal nerve (or one could say a single dorsal root or dorsal root ganglion). Adjacent dermatomes overlap, so that destruction of one dorsal root does not produce anesthesia of its dermatome (but does produce reduced sensation), whereas destruction of two adjacent dorsal roots does produce an area of complete insensitivity in the region of overlap.
A single dermatome usually involves several cutaneous nerves. Also, a single cutaneous nerve may relate to more than one dermatome. Think about this and be sure you understand it! Dermatomes are quite systematically arranged, but areas of skin innervated by cutaneous nerves are not. For the upper limbs, ventral rami of spinal nerves from several cord levels unite to form the brachial plexus wherein fibers are exchanged. The nerves emerging from this plexus, therefore, usually contain fibers from more than one cord level, and, likewise, each cord level is represented in several nerves. Hence, the cutaneous branches from the plexus convey fibers for more than one dermatome, and each dermatome sends fibers into more than one peripheral nerve.
6-4 - Bony Landmarks of the Upper limb
In order to understand the anatomy of the upper limb it is important to know a few key bony landmarks. Prior to dissection you should become familiar with the bones of the upper limb and important landmarks. The list below, with Netter for reference, indicates what is considered to be essential for you to learn now.
Clavicle, Netter, Plate 391 Radius, Netter, Plates 407, 409
-head
-radial tuberosity
-styloid process
Scapula, Netter, Plates 392-393 Ulna, Netter, Plates 407, 409
-spine -olecranon
-acromion -coronoid process
-supraspinous fossa -ulnar tuberosity
-infraspinous fossa -styloid process
-superior angle -trochlear notch
-inferior angle
-vertebral border Carpal bones, Netter, Plates 422-423
-axillary border -scaphoid
-glenoid fossa -lunate
-subscapular fossa -triquetral
-supraglenoid tubercle -pisiform
-infraglenoid tubercle -trapezium
-coracoid process -trapezoid
-capitate
-hamate
Humerus, Netter, Plates 392-393 Hand, Netter, Plate 426
-head -metacarpals
-anatomical neck -phalanges (proximal, middle and distal)
-surgical neck
-greater and lesser tubercle
-deltoid tuberosity
-capitulum
-trochlea
-lateral and medial epicondyle
6-5- Dissection of Axillary Nodes
The lymph from the breast is filtered mainly through the pectoral nodes. Because the efferent vessels from the pectoral nodes go to the central nodes which then drain to the apical nodes, it is unfortunately common in cases of breast cancer for clusters of cancerous cells to be carried to and thus involve the lymph nodes of the axilla. In a modified radical mastectomy, axillary nodes are excised up to the axillary vein. The vein is not stripped in order to avoid edema of the upper limb. This procedure may be followed by radiation therapy.
6-6
Posterior nerves of the brachial plexus innervate the posterior compartment muscles, and anterior nerves innervate anterior compartment muscles. In the upper limb the posterior muscles are largely extensors and the anterior muscles are largely flexors.
6-7 - Axillary Artery Collaterals
In our on-going discussion of collateral circulation, persistent blockage or slow occlusion of a major arterial route can cause originally small collaterals to adapt and enlarge to carry a significant volume of blood. In the case of a ligature around the first part of the axillary artery, several collateral routes are available which can bypass the blocked region of the artery. For example, the thyrocervical trunk (which is a branch of the subclavian) gives rise to a suprascapular branch. This anastomoses with the scapular circumflex branch of the subscapular artery which arises from the lower part of the axillary artery. This is an important route at the shoulder joint.
7. DISSECTION OF THE SHOULDER GIRDLE AND ARM
OBJECTIVES RESOURCES
1. Muscles of pectoral girdle
a. Demonstrate on a skeleton the a. Discussion 7-1.
axes through the sternoclavicular
joint which define elevation-
depression, protraction-retraction
and medial/lateral rotation of the
pectoral girdle.
b. Analyze the actions of the b. Cadaver, Skeleton, yourself;
following muscles on the Discussion 7-1.
pectoral girdle about each axis
through the sternoclavicular
joint:
- trapezius
- serratus anterior
- rhomboids
- pectoralis minor
- levator scapulae
2. Muscles acting at the shoulder joint.
a. Demonstrate on the skeleton the a. Discussion 7-2.
axes through the shoulder
(glenohumeral) joint which
define abduction-adduction,
flexion-extension and medial/
lateral rotation of the arm.
b. Analyze the actions of the b,c. Discussion 7-2; Cadaver;
following muscles on each Skeleton; yourself.
axis through the shoulder
joint:
- deltoid
- pectoralis major
- supraspinatus
- infraspinatus
- teres minor
- teres major
- latissimus dorsi
- subscapularis
- coracobrachialis
- biceps
- long head of triceps
OBJECTIVES RESOURCES
2c. Discuss the stabilizing role
of the "rotator" (musculo-
tendinous) cuff muscles.
3. Muscles of the arm acting
at the elbow joint
a. Demonstrate on the skeleton the a. Discussion 7-3.
axes through the elbow and
proximal radioulnar joints
which define flexion-extension
and pronation-supination.
b. Analyze the action of the b. Cadaver; Skeleton.
triceps, biceps and brachialis
muscles at the elbow joint and
the biceps at the proximal
radioulnar joint.
4. Nerves of arm and shoulder
a. Identify on the cadaver the following nerves a. Netter, Plate 401.
as they branch from the plexus:
- dorsal scapular (optional)
- long thoracic
- suprascapular
- medial and lateral pectoral
- upper, middle (thoracodorsal)
and lower subscapular
- medial antebrachial cutaneous
b. Indicate the nerve supply to
each muscle covered in this
dissection (associate innervation
with muscle compartments).
5. Arteries associated with brachium
Demonstrate on the cadaver the Netter, Plate 405;
following arteries: Discussion 6-8.
- brachial artery
- deep brachial
- superior ulnar collateral.
DISSECTION
Both upper limbs should be dissected.
1. Begin with the body in a prone position. With the exception of the levator scapulae, the latissimus dorsi, trapezius, and the rhomboideus major and minor muscles (Netter, Plates 178, 395) have already been reflected from their origins. Leave the attachments of the levator scapulae intact. You will need to cut the insertions of the trapezius muscle from the scapular spine and acromion process to gain access to the supraspinatus muscle (see below), but leave its attachment to the clavicle intact. As you reexamine these muscles, discuss their sites of attachment. Relocate the nerve supply to each of these muscles at the muscle. The origin of these nerves off the brachial plexus, with the exception of cranial nerve XI to the trapezius, will be followed in step #8.
2. Cut the deltoid muscle at its origin from the spine of the scapula and the outer surfaces of the acromion and clavicle and reflect it to its insertion on the deltoid tuberosity of the humerus. Relocate the axillary nerve and posterior humeral circumflex artery.
3. Identify and clean the supraspinatus, infraspinatus, teres minor and major muscles. Identify their attachments, but leave them intact (Netter, Plates 395-397).
4. Identify and clean the three heads (long, lateral and medial) of the triceps brachii (Netter, Plate 403). Find the radial nerve and deep brachial artery between the long and lateral heads of the triceps.
5. Now turn the body on its ba