Download arterial supply

Thoracic spinal
nerve
Lateral cutaneous
branch
Intercostal nerve
Anterior cutaneous
branch
External intercostal
muscle
Internal intercostal
muscle
Innermost intercostal
muscles
muscles
Several groups of muscles
are found in the chest wall.
Some of these muscles
attach ribs to other ribs,
while others join ribs and
sternum or vertebrae.
The function common to all of
these muscles is that they can
move the ribs, in addition to
whatever other movements
they produce. Movement of the
ribs is the fundamental action
producing respiration, as
detailed following.
The space between
adjacent ribs is filled with
a set of intercostal
muscles, of which there
are three layers-the
external, internal, and
innermost intercostal
muscles.
These muscle groups differ from
each other in the direction in
which their muscle fibres are
arranged and the degree to
which they are present at all
points around the full curvature
of the chest wall, from the
vertebral column posteriorly to
the costal cartilages anteriorly.

At points where an intercostal
muscle itself is not present, it is
represented by a membrane
(e.g., the external intercostal
muscle is not continuous all the
way anterior to the costal
cartilages, and, anteriorly, the
anterior intercostal membrane
is found in its place).
Also a separate and distinct 
muscle may be found in the plane
of the innermost intercostal
muscles and may be thought of
as a continuation of that layer of
intercostal musculature called
intercostalis intemus (e.g., the
transversus thoracis and
subcostal muscles).
Apart from the intercostal
muscles, the chest wall is an
attachment for many important
muscles of the upper limb
abdomen and neck. Movement
of the ribs is an essential part
of changing the shape and
volume of the chest and is
essential for respiration.
There is no agreement about the
activity of specific intercostal
muscles in the various phases of
respiration. Most agree that the
external intercostals are elevators of
the ribs (and therefore active in
inspiration), but the role of the
internal and the innermost
intercostals is unclear.
Eleven pairs of intercostal veins exist.
On both the right and left sides , the
first intercostal vein drains superiorly
and directly into the brachiocephalic
vein. On the right, intercostal veins 2
to 4 collect into a common trunk, the
right superior intercostal vein, which
drains into the azygos vein (an
important vein, which is a major
tributary of the superior vena cava).
The remaining intercostal veins on
the right (for interspaces 5 to 11)
drain directly into the azygos vein,
as it courses superior and just
anterior to the vertebral column.
On the left side, intercostal veins 2
and 3 form a left superior
intercostal vein, which crosses the
left side of the aortic arch to drain
into the left brachiocephalic vein.
Intercostal veins 4 to 11 remain
separate and drain independently
into the accessory hemiazygos
vein (for left intercostal veins 4 to
8), or the hemiazygos vein (for left
intercostal veins 9 to 11). In
midthorax, the accessory
hemiazygos vein crosses the
midline to drain into the azygos
vein.
The hemiazygos vein also
crosses the midline to drain into
the azygos vein or may instead
first join the accessory vein.
hemiazygos vein. In this fashion,
most of the venous drainage of
both sides of the chest wall
ultimately empties into the
azygos vein.
arterial supply
The arterial supply to the chest wall
arises in two main sources: the intercostal
vessels and the various branches of the
subclavian and axillary arteries that reach
the chest. Each intercostal artery runs a
roughly semicircular course, arising
posteriorly (from different sources) and
coursing around the chest wall to unite
with the internal thoracic artery anteriorly.
The component originating from the
aorta (or other posterior source) is
called the posterior intercostal artery
and the component branching from
the internal thoracic artery is known
as the anterior intercostal artery,
although in fact they form one single
continuous vessel. Along its course
each artery gives off several
branches, supplying nearby muscles,
connective tissues, bones, and skin.
The collateral supply between
intercostal spaces is so extensive that
to produce ischaemic injury to just one
intercostal space if they ocluded . The
origins of the 12 intercostal arteries are
subject to considerable variation. The
upper two intercostal arteries, on both
sides, usually arise from the left and
right superior or suprime intercostal
arteries, themselves branches of the
costocervical trunk of the subclavian
artery.
These upper intercostal arteries arch
posteriorly, drape over the apex of
each lung, and then turn inferiorly to
lie just anterior to the necks of ribs 1
and 2. Here vessels assume a
position just inferior to the rib and
course anteriorly around the chest
wall as the first and second
intercostal arteries. The second
intercostal artery forms collateral
connections with the third intercostal
artery.
Segmental arteries for the next
nine intercostal spaces (i.e.,
intercostal arteries 3 to 11) arise
from the thoracic (descending)
aorta in pairs (one each for left
and right side of the chest wall).
The 12th intercostal artery lying
inferior to the 12th rib, also
arises from the aorta and is
known as the subcostal artery.
Because the aorta lies on the
left side of the posterior
thoracic wall, the lower nine
right intercostal arteries are
longer than the lower nine
intercostal arteries on the left.
As they move toward the right
side, the right side intercostal
arteries 3 to 12 pass anterior to
the vertebrae but posterior to
the oesophagus, thoracic duct,
The lower nine left intercostal arteries,
originating from the aorta, simply move
laterally into the intercostal space, lying
posterior to the hemiazygos and azygos
veins. On both the left and right sides, the
sympathetic trunks lie anterior to the
intercostal arteries at all levels.
Moving from anterior to posterior, a series
of separate arteries helps supply the chest
wall. Each also forms anastomoses with
intercostal arteries in the area of the chest
supplied..
The internal thoracic artery arises
from the inferior surface of the
first part of the subclavian artery
and travels inferiorly down the
inner surface of the chest wall,
just deep to the costal cartilages.
It lies about 1 cm lateral to the
margin of the sternum. At the
level of the sixth rib, it divides into
its terminal musculophrenic and
superior epigastric branches.
The superior thoracic artery is a small
branch of the first part of the axillary
artery.
It passes medial to the pectoralis minor
and anastomoses with the upper two to
three intercostal arteries. The lateral
thoracic artery is another branch of the
axillary artery, from its second part. It
descends along the lateral border of
the pectoralis minor and supplies many
muscles on the anterolateral chest wall.
The lateral thoracic artery anastomoses with the
internal thoracic, subscapular, and intercostal
arteries. In the female it has an especially large
branch supplying the breast. The subscapular
artery, arising from the third part of the axillary
artery, descends along the posterior axillary
wall parallel to the inferior border of the
latissimus dorsi. It anastomoses with many
other arteries around the scapula and with the
lateral thoracic and intercostal vessels as well.
The dorsal scapular artery arises from the
subclavian artery, passes to the posterior side
of the trunk, and descends along the medial
border of the scapula, deep to the rhomboid
muscles. It anastomoses with the upper
posterior intercostal arteries.
Lateral
cutaneous
Aorta
Posterior intercostal
artery
branch
Anterior
intercostal
branch
Internal thoracic artery
Eleven pairs of intercostal nerves course
between adjacent ribs, and the subcostal
nerves course below each 12th rib. These
nerves are the continuation of the ventral
primary rami of thoracic segments of the
spinal cord. The intercostal nerves travel
just inferior to the inferior margin of the
rib, in the costal groove.
Each intercostal nerve contains somatic
sensory and motor axons as well as
sympathetic axons that innervate sweat
glands, arrector pili muscles (for the
elevation of hairs), and vascular smooth
muscle. Each intercostal nerve innervates
deep structures, such as the intercostal
muscles, the lateral rim of the diaphragm,
and the parietal pleura, and has
cutaneous branches innervating the skin
and superficial fasciae. Intercostal nerves
7 to 12 continue inferomedially to
innervate the abdominal wall.
Intercostal Nerve Block
1.
Costal angle
(mostly)
2.
Posterior axillary
line
3.
Anterior axillary
line
Intercostal Nerve Block