DISSECTION 18
The Thoracic Wall and Pleura
References: M1 72-97, 106-111; N 178-188, 192-194, 226-227; N 185-194, 196-198, 230-231;
R 195-201, 254-255
AT THE END OF THIS LABORATORY PERIOD YOU WILL BE RESPONSIBLE FOR THE
IDENTIFICATION AND DEMONSTRATION OF THE STRUCTURES LISTED BELOW:
1.
Bones and bony features: sternum [manubrium (clavicular notch, suprasternal (jugular) notch),
body of the sternum (costal notches), xiphoid process] manubriosternal synchondrosis,
sternoclavicular joint, sternal angle; ribs (head, neck, tubercle, costal angle, costal groove), costal
cartilages, thoracic vertebrae (facets on bodies for head of rib, facets on transverse process for
tubercle of rib).
2. Muscles and fascia: external intercostal, external intercostal membrane, internal intercostal,
innermost intercostal, transversus thoracis.
3. Nerves: intercostal.
4. Vessels: posterior intercostal, anterior intercostal, internal thoracic artery and vein.
5. Serous membranes: parietal pleura, (costal, cervical, mediastinal, diaphragmatic),
costomediastinal reflection, costodiaphragmatic reflection, visceral pleura.
6. Subdivisions of the pleural cavity: costomediastinal recess, costodiaphragmatic recess.
YOU SHOULD ALSO BE ABLE TO DO THE FOLLOWING THINGS:
1. State the characteristics of thoracic vertebrae and the changes one encounters in moving from
upper to lower thoracic regions.
2. Identify the basic features of a rib and special characteristics of the first rib and lower five
"false ribs".
3. Describe the basic movement of the ribs in respiration and name the major muscles involved in
inspiration and expiration.
4. State the relationship of the intercostal vessels and nerves to the intercostal muscles.
5. Define the following terms: pleura, pleural cavity, pleural recess, pleural reflection, mediastinum
and visceral, parietal, costal, cervical, mediastinal and diaphragmatic pleura.
6. Draw and label on a diagram of the thoracic wall the approximate position of the pericardial sac
and the lines of reflection of the parietal pleura.
7. Label on a diagram a typical intercostal nerve or artery and its branches; be aware of the general
distribution of the branches.
8. List the types of fibers found in an intercostal nerve and its muscular and cutaneous branches.
Locate the cell bodies of origin of each type of fiber.
The Thoracic Wall
Before beginning the dissection identify on
the skeleton the bones and bony features listed
above.
Then on the cadaver palpate the
STERNOCLAVICULAR
JOINTS,
the
SUPRASTERNAL NOTCH, the MANUBRIUM, BODY
OF THE STERNUM and the STERNAL ANGLE
between them. Note that the first rib articulates
Dissection 18, Thoracic Wall and Pleura
with the manubrium near the sternoclavicular
joint, the second rib articulates with the sternum
at the sternal angle and the remaining five true
ribs articulate with the body of the sternum.
Besides the seven true ribs there are five "false"
ribs, three of which articulate anteriorly by means
of a common cartilage attached at the xiphisternal
junction and two of which, the "floating" ribs,
have no anterior attachment (G1.9A; N178; N185;
A149).
Carefully dissect the structures in an
intercostal space (the area between two ribs).
Note that the EXTERNAL INTERCOSTAL MUSCLE
does not reach to the sternum but is replaced by
an EXTERNAL INTERCOSTAL MEMBRANE. Deep
to this muscle is the INTERNAL INTERCOSTAL
MUSCLE whose fibers run almost at right angles
to those of the external intercostal.
The
intercostal vessels and nerves run in the cranial
part of the intercostal spaces just below the ribs
deep to the internal intercostal muscle. The
POSTERIOR INTERCOSTAL VEIN lies in the
COSTAL GROOVE, just internal to the inferior
border of the rib, and the POSTERIOR
INTERCOSTAL ARTERY and the INTERCOSTAL
NERVE are just below the vein in that order
(N184; N191). Near the midaxillary line the
INNERMOST INTERCOSTAL MUSCLE layer can be
seen.
The intercostal vessels and nerves lie between
the innermost intercostal and internal intercostal
muscles and these are the best guides for
distinguishing between these two muscle layers.
Posteriorly the internal intercostal muscle does
not reach the vertebral column but is replaced by
the internal intercostal membrane (G1.15, 18;
N187; N192). This will be seen when the
posterior wall of the thorax is dissected. Remove
the external intercostal membrane and the deeper
internal intercostal muscle for an inch or so lateral
to the sternum in each of the intercostal spaces.
Leave the underlying pleura intact (G1.19, 20, 26;
A182). This will reveal the vertically running
INTERNAL THORACIC ARTERY and VEIN (A146;
N184; N191). The ANTERIOR INTERCOSTAL
ARTERIES arise from the artery and the vein
receives
as
tributaries
the
ANTERIOR
INTERCOSTAL VEINS. The anterior intercostal
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vessels are continuous with the posterior
intercostal vessels, which have their origin from
the thoracic aorta or terminate in the azygos or
hemiazygos veins (G1.15, 75, 76; A233, 234, 235;
N183, 184, 187; N189, 191, 192).
The first intercostal space is an exception to
this general vascular pattern in that it is usually
supplied by a costal branch from the costocervical
trunk of the subclavian artery (A233).
In
preparation for removal of the anterior thoracic
wall be sure to leave the previously dissected
intercostal muscles intact, but remove the
remaining intercostal musculature from the upper
seven interspaces on both sides as far laterally as
the midaxillary line, carefully avoiding damage to
the parietal pleura.
Using your fingertips,
depress the pleura from the thoracic wall, to
which it is usually bound by a small amount of
connective tissue, the endothoracic fascia. When
the parietal pleura has been freed, the sternum and
ribs may be divided.
Rib and Sternal Incisions
To remove the anterior thoracic wall, reflect the
serratus anterior to the midaxillary line and divide
the manubrium transversely above the sternal
angle, but keep the sternoclavicular joint intact.
Cut the second through the fifth ribs in the
midaxillary line and sever the sternum once more,
below its junction with the fifth pair of COSTAL
CARTILAGES.
Dissection 18, Thoracic Wall and Pleura
After removing the sternum and ribs
demonstrate the INTERNAL THORACIC ARTERIES
(G1.19, 20; N184; N191; A162); these are
branches of the subclavian arteries. Look for
their ANTERIOR INTERCOSTAL BRANCHES. How
many are present in each interspace? What are
the terminal branches of the internal thoracic
arteries? Note any retrosternal lymph nodes and
vessels. The TRANSVERSUS THORACIS MUSCLE,
the sternal representation of the innermost
intercostal, should also be identified. Retain the
detached sternum and ribs for further study.
As the dissection proceeds, occasionally
replace the excised portion of the thoracic cage to
review the thoracic visceral topography. Give
particular attention to the relation of the pleura,
heart, and great vessels to the anterior thoracic
wall.
The Pleura
Each lung is enveloped by a serous
membrane, the VISCERAL PLEURA (G1.24C, 26;
N194; N198; A168-171), which is continuous
with the PARIETAL PLEURA lining the thoracic
wall (G1.24C; N194; N198; A163). These two
membranes are continuous with each other at the
hila of the lungs. The VISCERAL PLEURA
intimately invests the lung and is not separable
from it. The parietal pleura is adherent to the
internal surface of the thoracic wall by the
endothoracic fascia. Between the parietal pleura
and the visceral pleura is a potential space
containing only a thin film of serous fluid. This
potential space is called the PLEURAL CAVITY
(N192, 193; N196-197). The parietal pleura,
visceral pleura and pleural cavity of the right side
make up the right pleural sac, which is not
continuous with that of the left side. The parietal
pleura is subdivided for convenience of
description and named according to its location.
Distinguish the COSTAL (lining the ribs),
CERVICAL (extending above the first rib into the
root of the neck), MEDIASTINAL, and
DIAPHRAGMATIC components of the parietal
pleura. These subdivisions of the parietal pleura
are, of course, continuous with one another where
they "reflect" from contact with one surface to
another.
Observe on the specimen the
COSTODIAPHRAGMATIC (N192; N196) and
Page 3
REFLECTIONS of the
parietal pleura (G1.68; A163). What is the rib
level of the costodiaphragmatic reflection in the
midaxillary line? (G1.26; A166, 167).
COSTOMEDIASTINAL
In quiet respiration the lungs are not
expanded fully, and the parietal pleura is not
everywhere in contact with the visceral pleura
covering the lungs. Below the lower border of the
lung (eighth rib) the costal and diaphragmatic
portions of the parietal pleura are in apposition.
Similarly, anteriorly, the costal and mediastinal
parietal pleurae are in apposition along the line of
reflection. These areas within the parietal pleura
which are not in direct contact with visceral
pleura of the lung are called "recesses" or
"sinuses."
Thus
there
are
COSTODIAPHRAGMATIC
RECESSES
and
COSTOMEDIASTINAL RECESSES in each pleural
cavity. Some of these recesses allow a needle to
be placed in the pleural space with little danger of
damage to the lung. What is this procedure
called? For what purpose is this done?
After inspecting and palpating the extensions
of the parietal pleura, make an incision in the
parietal pleura over each lung as indicated in the
previous diagram.
Place your hand in the
PLEURAL CAVITY, and explore the limits of the
cavity, noting the costodiaphragmatic and
costomediastinal recesses in particular.
Dissection 18, Thoracic Wall and Pleura
Put your fingertips in each costomediastinal
recess. Is the space continuous across the
midline? Can you pass your hand from one
pleural cavity into the one on the opposite side
dorsal to the pericardial sac? Does your cadaver
Page 4
have any strands of connective tissue attaching
the adjacent visceral and parietal pleurae over
the convexity of the lung? What are such
connections called? What is the origin of these
connections?
______________________________________________________________________________________________
STUDY QUESTIONS
1.
Localize the position of the pericardial
sac with respect to the anterior thoracic wall.
1.
See M1 171-173 or G1.42.
a. The apex is in the 5th. interspace just
medial to the midclavicular line.
b. The right border extends from the 3rd
costal cartilage to the 6th costal cartilage a
fingerbreadth from the right margin of the
sternum.
c. The inferior border lies along a line
from the inferior end of the right border
through the xiphisternal joint to the apex.
d. The left border lies along a line from the
apex to the second interspace a
fingerbreadth to the left of the sternum.
e. The superior border lies along a line from
the left second interspace to the right third
costal cartilage.
2.
What are the divisions of the
thoracic cavity?
2.
The thoracic cavity is divided into the right and
left pleural cavities and the mediastinum.
3.
What are the normal contents of
the pleural cavities?
3.
Only a capillary layer of serous fluid.
4.
Name and define the subdivisions
of the pleura.
4.
The visceral pleura is the serous membrane that
covers the lung everywhere except at the root of
the lung. The parietal pleura lines the thoracic
wall. It has four components which are
1) the costal pleura which lines the inner
surface of the ribs and costal cartilages and the
intercostal muscles;
2) the mediastinal pleura which covers the
mediastinum;
3) the diaphragmatic pleura, which covers the
superior surface of the diaphragm lateral to the
mediastinum; and the cervical pleura, which
extends into the root of the neck.
Dissection 18, Thoracic Wall and Pleura
Page 5
5.
What are the lines of pleural reflection?
5.
The lines of pleural reflection mark where the
costal pleura becomes continuous with
mediastinal pleura and with the diaphragmatic
pleura.
6.
Where does the sternal (anterior
costomediastinal) reflection of the
pleura deviate from the midline?
6.
Above the sternal angle on both sides; behind the
xiphoid process on the right side and at the 4th
costal cartilage on the left side.
7.
Where does the costodiaphragmatic
reflection cross the
a) midclavicular line?
b) midaxillary line?
c) body of the vertebra?
7.
8.
Where do the reflections of the
parietal pleura pass beyond the
limits of the thoracic skeleton?
8.
At the right xiphisternal angle, at both right and
left costovertebral angles (below 12th ribs), and
above the anterior portions of both first ribs.
9.
What is the pulmonary ligament?
9.
The pulmonary ligament is a double layered
reflection of mediastinal pleura that becomes
continuous with visceral pleura below the root of
the lung.
a.
b.
c.
8th rib
10th rib
below the 12th rib
10. Discuss the innervation of the pleura.
Is the pleura sensitive to pain? Is there
pain referral from the pleura to other
parts of the body?
10. The costal pleura and peripheral part of the
diaphragmatic pleura are innervated by
intercostal nerves and are quite sensitive to pain.
The mediastinal pleura and central part of the
diaphragmatic pleura are innervated by the
phrenic nerve, and pain from these regions tends
to be referred to the lower neck and shoulder.
Why? The visceral pleura is insensitive to pain.
11. Add lines of pleural reflection to a diagram
of the thoracic skeleton.
11.
Dissection 18, Thoracic Wall and Pleura
12. From what artery is the internal
thoracic a branch?
What are the branches of the
internal thoracic?
Underline the terminal branches.
To what vessel does the internal
thoracic vein drain?
13. Define:
Pleural cavity
Page 6
12. The subclavian
Pericardiacophrenic, thymic, sternal, mediastinal,
anterior intercostal, perforating,
musculophrenic, and superior epigastric.
The brachiocephalic vein.
13. Potential space between parietal and
visceral pleurae.
Costomediastinal recess
Pleural "space" along the anterior pleural
reflection where the parietal pleura is not in
contact with the lung (visceral pleura).
Costodiaphragmatic recess
Pleural space between the eighth and tenth ribs
in the midaxillary line into which the lung does
not extend in quite respiration; lined
peripherally by costal (parietal) pleura and
centrally by diaphragmatic (parietal) pleura; a
common site for thoracentesis.
14. The sternal angle is a surface landmark
of considerable importance. What structures
lie deep to it?
14. The sternal angle marks the junction of the
second ribs with the sternum and also is at the
level of the disk between T4 and T5. The
bifurcation of the trachea and the beginning and
end of the aortic arch lie at this level. A
horizontal plane through the sternal angle is the
boundary between the superior mediastinum and
the inferior mediastinum.
15. What structure is in direct relationship to the left sides of the bodies of the middle four thoracic vertebrae?
16. What is the nature of the union between rib and costal cartilage? Between costal cartilage and sternum?
17. Define the term "thoracic inlet". Give its boundaries.
18. Define the term "thoracic outlet". Give its boundaries.
Dissection 18, Thoracic Wall and Pleura
Page 7
19. What is a dermatome?
19. A dermatome is the region of skin supplied by the
afferent fibers of a single spinal nerve.
20. Which spinal nerve supplies the
dermatome including:
a. the nipple?
b. the infrasternal angle?
c. the umbilicus?
20.
21. Describe the movements of the
ribs in inspiration and expiration.
21.
a.
b.
c.
T4
T7
T10
M1 Fig. 1.10,p82
LJ:bh
revised 06/18/09