The document describes the muscles and nerves of the thoracic wall. It discusses the three layers of intercostal muscles - external, internal, and innermost. It also describes the intercostal nerves, noting the typical arrangement from T3-T6, and variations in other regions. Finally, it discusses the diaphragm muscle, its origins along the ribs and vertebrae, openings, nerve supply, and role in respiration.

1. Muscles and nerves in the
thoracic wall
Dr. Mohammed Mahmoud Mosaed

2. Intercostal Spaces
• The intercostal space is the space between 2 ribs and
their costal cartilages
• Contents
• Intercostal muscles; three muscles of respiration: the
external intercostal, the internal intercostal, and the
innermost intercostal muscle. The innermost
intercostal muscle is lined internally by the
endothoracic fascia, which is lined internally by the
parietal pleura.
• The intercostal nerves and blood vessels run between
the intermediate and deepest layers of muscles. They
are arranged in the following order from above
downward: intercostal vein, intercostal artery, and
intercostal nerve (i.e., VAN)

5. Intercostal Muscles
• The external intercostal muscle forms the
most superficial layer. Its fibers are directed downward
and forward. The muscle extends forward to the costal
cartilage where it is replaced by an aponeurosis, the
anterior (external) intercostal membrane
• Origin; from the inferior border of the rib above
Insertion; into the superior border of the rib below
• Nerve supply; Intercostal nerves; T1-T11
• Action; Most active during inspiration; supports
intercostal space; moves ribs superiorly

6. • The internal intercostal muscle forms
the intermediate layer. Its fibers are directed
downward and backward. The muscle extends
backward from the sternum in front to the
angles of the ribs behind, where the muscle is
replaced by an aponeurosis, the posterior
(internal) intercostal membrane
• Origin; from the lateral edge of the subcostal
groove of the rib above
• Insertion; into the upper border of the rib
below
• Nerve supply; Intercostal nerves; T1-T11
• Action; Most active during expiration; supports

9. • The innermost intercostal muscle forms
the deepest layer. It is related internally to fascia
(endothoracic fascia) and parietal pleura and
externally to the intercostal nerves and vessels. Its
fibers have the same orientation as the internal
intercostals. These muscles are most evident in the
lateral thoracic wall
• Origin: Medial edge of costal groove of rib above
• Insertion: Internal aspect of superior border of rib
below
• Nerve supply: Intercostal nerves; T1-T11
• Action: Acts with internal intercostals muscles
• The innermost intercostal muscle can be divided into
three portions. which are more or less separate from
one another; innermost intercostal, subcostal and
transversus thoracis muscles

10. Action of the intercostal muscles
• When the intercostal muscles contract, they all tend to
pull the ribs nearer to one another.
• If the 1st rib is fixed by the contraction of the scaleni
muscles, the intercostal muscles raise the 2nd
to the
12th
ribs toward the first rib, as in inspiration.
• If, conversely, the 12th
rib is fixed by the quadratus
lumborum muscle and the oblique muscles of the
abdomen, the 1st
to the 11th
ribs will be lowered by the
contraction of the intercostal muscles, as in expiration.
• In addition, the tone of the intercostal muscles during
the different phases of respiration serves to strengthen
the tissues of the intercostal spaces, thus preventing
the sucking in or the blowing out of the tissues with
changes in intrathoracic pressure

11. Intercostal Nerves
• The intercostal nerves are the anterior rami of
the first 11 thoracic spinal nerves.
• The anterior ramus of the 12th
thoracic nerve
lies below the 12th
rib in the abdomen and called
the subcostal nerve.
• The intercostal nerves from 3rd
to the 6th
nerve
has the same course and the same branches
so they called typical intercostal nerves
• 1, 2 and 7-11 intercosal nerves are atypical
intercostal nerves

12. Course of typical intercostal nerve
• Each intercostal nerve enters an intercostal space
between the parietal pleura and the posterior
intercostal membrane.
• It then runs forward inferior to the intercostal vessels
in the subcostal groove of the corresponding rib,
between the innermost intercostal and internal
intercostal muscle. Near the sternum, they cross
anterior to the internal thoracic vessels and
transversus thoracis,
• It pierces the internal intercostals, the external
intercostal membranes and pectoralis major, and end
as the anterior cutaneous nerves of the thorax

13. Branches
• Rami communicantes connect the intercostal nerve to
a ganglion of the sympathetic trunk.
• The collateral branch runs forward inferiorly to the
main nerve on the upper border of the rib below.
• The lateral cutaneous branch reaches the skin on the
side of the chest. It divides into an anterior and a
posterior branch.
• The anterior cutaneous branch, which is the terminal
portion of the main trunk, reaches the skin near the
midline. It divides into a medial and a lateral branch.
• Muscular branches run to the intercostal muscles.
• Pleural sensory branches go to the parietal pleura.

14. Atypical intercostal nerves
• The first intercostal nerve is joined to the brachial plexus
by a large branch. The remainder of the first intercostal
nerve is small, and there is no anterior cutaneous branch.
• The second intercostal nerve is joined to the medial
cutaneous nerve of the arm by a branch called the
intercostobrachial nerve. The second intercostal nerve
therefore supplies the skin of the armpit and the upper
medial side of the arm.
• The 7th to the 11th intercostal nerves
The seventh to ninth intercostal nerves leave the anterior
ends of their intercostal spaces by passing deep to the
costal cartilages, to enter the anterior abdominal wall.
The 10th and 11th nerves, since the corresponding ribs are
floating, pass directly into the abdominal wall

15. Suprapleural Membrane
• It is a tent-shaped dense fascial sheet
• attached laterally to the medial border of the first rib
and costal cartilage. It is attached at its apex to the tip
of the transverse process of the seventh cervical
vertebra and medially to the fascia investing the
structures passing from the thorax into the neck
• It protects the underlying cervical pleura and resists
the changes in intrathoracic pressure occurring during
respiratory movements.
• Endothoracic Fascia
• The endothoracic fascia is a thin layer of loose
connective tissue that separates the parietal pleura
from the thoracic wall.
• The suprapleural membrane is a thickening of this
fascia.

16. Diaphragm
• The diaphragm is a thin muscular and
tendinous septum that separates the chest
cavity above from the abdominal cavity
below. It is pierced by the structures that
pass between the chest and the abdomen.
• The diaphragm is the most important
muscle of respiration.
• It is dome shaped and consists of a
peripheral muscular part, and a centrally
placed tendon

19. The origin of the diaphragm
• The origin of the diaphragm divided into
three parts:
• A sternal part arising from the posterior
surface of the xiphoid process
• A costal part arising from the deep
surfaces of the lower six ribs and their
costal cartilages
• A vertebral part arising by vertical
columns or crura and from the arcuate
ligaments

20. Vertebral origin of the diaphragm
• The right crus arises from the sides of the bodies of the first
three lumbar vertebrae and the intervertebral discs;
• the left crus arises from the sides of the bodies of the first
two lumbar vertebrae and the intervertebral disc .
• Lateral to the crura the diaphragm arises from the medial
and lateral arcuate ligaments
• The medial arcuate ligament extends from the side of the
body of the second lumbar vertebra to the tip of the
transverse process of the first lumbar vertebra
• The lateral arcuate ligament extends from the tip of the
transverse process of the first lumbar vertebra to the lower
border of the 12th rib.
• The medial borders of the two crura are connected by a
median arcuate ligament, which crosses over the anterior
surface of the aorta

22. Insertion of the diaphragm
• The diaphragm is inserted into a central
tendon, which is shaped like three leaves.
The superior surface of the tendon is partially
fused with the inferior surface of the fibrous
pericardium. Some of the muscle fibers of the
right crus pass up to the left and surround the
esophageal orifice in a slinglike loop.
• These fibers appear to act as a sphincter and
possibly assist in the prevention of regurgitation
of the stomach contents into the thoracic part of
the esophagus

24. Shape of the Diaphragm
• As seen from in front, the diaphragm curves up into right
and left domes or cupulae.
• The right dome reaches as high as the upper border of the
fifth rib, (The right dome lies at a higher level, because of
the large size of the right lobe of the liver.)
• The left dome may reach the lower border of the fifth rib.
• The central tendon lies at the level of the xiphisternal joint.
• The domes support the right and left lungs, whereas the
central tendon supports the heart.
• When seen from the side, the diaphragm has the
appearance of an inverted J, the long limb extending up
from the vertebral column and the short limb extending
forward to the xiphoid process

25. Openings in the Diaphragm
• The diaphragm has three main openings:
• The aortic opening lies anterior to the body of the 12th
thoracic vertebra
between the crura. It transmits the aorta, the thoracic duct, and the azygos
vein.
• The esophageal opening lies at the level of the 10th
thoracic vertebra
in a sling of muscle fibers derived from the right crus. It transmits the
esophagus, the right and left vagus nerves, the esophageal branches of the
left gastric vessels, and the lymphatics from the lower third of the
esophagus.
• The caval opening lies at the level of the 8th
thoracic vertebra in the
central tendon. It transmits the inferior vena cava and terminal branches of
the right phrenic nerve.
• In addition to these openings;
• The sympathetic splanchnic nerves pierce the crura;
• The sympathetic trunks pass posterior to the medial arcuate ligament on
each side;
• The superior epigastric vessels pass between the sternal and costal
origins of the diaphragm on each side

27. Nerve Supply of the Diaphragm
• Motor nerve supply: The right and left
phrenic nerves (C3, 4, 5(
• Sensory nerve supply: The central part
of the diaphragm is from the phrenic nerve
and the periphery of the diaphragm is from
the lower six intercostal nerves.
Action of the Diaphragm
• On contraction, the diaphragm pulls down its central
tendon and increases the vertical diameter of the
thorax

29. Functions of the Diaphragm
• Muscle of inspiration:The diaphragm is the most important muscle
used in inspiration.
• Muscle of abdominal straining:The contraction of the diaphragm
assists the contraction of the muscles of the anterior abdominal wall
in raising the intra-abdominal pressure for micturition, defecation, and
parturition..
• Weight-lifting muscle: the diaphragm assists the muscles of the
anterior abdominal wall in raising the intra-abdominal pressure to
such an extent that it helps support the vertebral column and prevent
flexion. This greatly assists the postvertebral muscles in the lifting of
heavy weights.
• Thoracoabdominal pump: The descent of the diaphragm decreases
the intrathoracic pressure and at the same time increases the intra-
abdominal pressure. This pressure change compresses the blood in
the inferior vena cava and forces it upward into the right atrium of the
heart, and lymph vessels is also compressed, and its passage
upward within the thoracic duct is aided by the negative intrathoracic
pressure. The presence of valves within the thoracic duct prevents
backflow.

30. Clinical note
• Hiccup
• Hiccup is the involuntary spasmodic contraction
of the diaphragm accompanied by the
approximation of the vocal folds and closure of
the glottis of the larynx. It is a common
condition in normal individuals and occurs after
eating or drinking as a result of gastric irritation
of the vagus nerve endings. It may, however,
be a symptom of disease such as pleurisy,
peritonitis, pericarditis, or uremia.

31. • Levatores Costarum
• There are 12 pairs of muscles. Each levator costa is triangular in shape and
arises by its apex from the tip of the transverse process and is inserted into
the rib below.
• Action: Each raises the rib below and is therefore an inspiratory muscle.
• Nerve supply: Posterior rami of thoracic spinal nerves
• Serratus Posterior Superior Muscle
• It is a thin, flat muscle that arises from the lower cervical and upper thoracic
spines. Its fibers pass downward and laterally and are inserted into the
upper ribs.
• Action: It elevates the ribs and is therefore an inspiratory muscle.
• Nerve supply: Intercostal nerves
• Serratus Posterior Inferior Muscle
• The serratus posterior inferior is a thin, flat muscle that arises from the upper
lumbar and lower thoracic spines. Its fibers pass upward and laterally and
are inserted into the lower ribs.
• Action: It depresses the ribs and is therefore an expiratory muscle.
• Nerve supply: Intercostal nerves