CHEST

The thoracic cage, delimited by the 12 pairs of ribs that articulate anteriorly with the sternum and
posteriorly with the dorsal column, is closed at the bottom through a muscle, the diaphragm, which in turn
divides the thoracic cavity from the abdominal cavity.
Inside the thorax box, it has organs of relevant importance such as the heart and lungs.

PREVIOUS VIEW

REAR VIEW

4*. 5* and 7*
SIDE VIEW TRUE RIBS

Thoracic
vertebrae

9* thoracic
vertebra

11* and 12*

FAKE RIBS
thoracic
vertebrae

1*lumbar
FLOATING
vertebra
RIBS

M. Faes--2011

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The ribs
The ribs are flat bone classification by their function. They have an arched shape and have different names
due to the way they articulate with the sternum. So we have:
• 7 pairs of true ribs; which are those that have an exclusive articular surface
for each one with the sternum;
• 3 pairs of false ribs; which unite into a large common costal cartilage to take insertion into
the sternum;
• 2 pairs of floating ribs; that do not have articulation with the sternum since they are very short and
They never reach it.

All ribs have common elements:

• the head
• he neck
• he articular tubercle for the vertebra
• he body
• articular surface for the sternum (costochondral junction
and costal cartilage)

The sternum

The sternum, unique and odd, is a flat classification bone because it fulfills an important protective function.
It closes the rib cage in front and provides articular surfaces for the ribs. It has three fundamental parts: the
manubrium, where the clavicle is articulated (Art. Sternoclavicular), the body, where most of the ribs
articulate (Art. Chondrosternal) and the xiphoid appendage, which is an important muscular origin, for
example, that of the abdominal muscles.

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The joints of the chest
The costovertebral joints are those formed between the two hemilaterals of the vertebral body and the
transverse process. These joints, therefore, are divided into:

Rib head or costovertebral

joint
Articular surfaces: facet of the
vertebral body and head of the rib.
It is an arthroid, in which sliding
movements occur.
Ligaments: Superior
costotransverse ligament (from the
rib to the transverse process of the
upper vertebra) | Radiated ligament
of the head of the rib (connects rib
to vertebral body) | Costotransverse
ligament (attaches transverse
process to head of rib) | Lateral
costotransverse ligament (attaches
rib to the transverse process).

Costotransverse joint:
Articular surfaces: transverse
process and tubercle of the rib
It is an arthroid, in which there are sliding movements
Bucket handle movements: the caudal ribs make this bucket handle movement, but the more cranial ones,
as the angle is flatter, move forward dragged by the sternum.

Costosternal joint:
STERNAL COST JOINT

It is the one that joins the rib to the

sternum, by means of a cartilage (the
costal cartilage)
Its structure is composed of the body of the
sternum and the costal cartilage that joins
the bony portion.
The costal (hyaline) cartilage is flexible and
rotates with inspiration. With age it ossifies
and breathing is made difficult by this fact.

Chest muscles
Serratus posterosuperior muscle: elevates the ribs (accessory to inspiration). From C5 to D2 to the 5th,
6th and 7th ribs.

Serratus posteroinferior muscle: descends the ribs (accessories of expiration). From D12 to L3 to the
9th, 10th, 11th and 12th ribs.

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Intercostal muscles : innervated by the intercostal nerves.
1. External intercostal muscles: elevate the ribs (accessories of inspiration).
2. Intermediate intercostal muscles: descend the ribs (accessory to expiration).
3. Intimate or internal intercostal muscles: they descend the ribs (accessories of the
expiration).

Each intercostal space contains: three muscles (musc. external, musc. intermediate and music intimal) and
the intercostal neurovascular bundle (intercostal artery, intercostal vein, intercostal nerve). It should be
noted that the intercostal neurovascular bundle is cranial within the intercostal space (important for
injections, cuts, etc.).

INTERCOSTAL MUSCLES

INTERNAL

M. Faes--2011

diaphragm muscle

The diaphragm muscle is the structure responsible for dividing the thoracic cavity from the abdominal cavity.
It attaches to the bottom of the chest wall. It is a flat or wide muscle. It is innervated by the phrenic nerve. It
is the most important inspiring muscle (as a physiological note, we can say that tetanus causes death due
to the tetanic (permanent) contraction of this muscle, among others, causing respiratory failure and death by
drowning).
There is an area of the pericardium attached to the diaphragm and when it moves, the heart also moves.
The diaphragm also attaches to the pleurae of the lungs and when the diaphragm moves, so do the lungs.
The diaphragm, at the bottom, joins the peritoneum.

The diaphragm originates from three bony portions:

•Lumbar portion:
o Right medial pillar (from L1-L4)
o Left medial pillar (from L1-L3)
o Lateral pillar: medial arcuate ligament (from the body of L1 to the transverse process of
L1) [Psoas Major arch] | lateral arcuate ligament (from the transverse process of L1 to
the tip of the 12th rib) [Arch of the quadratus lumborum] | middle arcuate ligament
(connects the two anterior pillars).
• Costal portion : from rib 12 to rib 7

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 • Sternal portion : xiphoid process of the sternum.

The diaphragm has more holes through which elements pass to communicate the two cavities (thoracic and
abdominal), but there is no real communication between the thorax and abdomen since the holes are
covered by the elements that cross them and by connective tissue. These holes are:

• Phrenic or tendon center: it is the insertion aponeurosis of the diaphragm. Through it passes the
inferior vena cava and the right phrenic nerve, has a non-contractile hiatus (1 in the image).
• Aortic hiatus: formed by the middle arcuate ligament (joins the two medial pillars) and the
spine. The aorta artery and the thoracic lymphatic duct (2 in the image) pass through it.
• Esophageal hiatus: located in the middle of the muscle fibers of the medial pillar. It is a hiatus with
contractile capacity. The esophagus and the vagus or pneumogastric nerves cross through it (3 in
the image).
• Hiatus of the Greater Vena Cava: crosses the phrenic center (4 in the image).
• In addition to inspiration, the diaphragm intervenes in the acts of expulsion: defecating, coughing,
giving birth,
vomiting, blowing, whistling, laughing, sneezing and talking.

DIAPHRAGM

M. Faes--2011
TOP VIEW
SELF-TEST

Seminar: Thorax

Questions
1) How is the thorax composed?
2) What are the intercostal muscles? What functions do they fulfill?
3) How does the thorax move? What are your joints?
4) What function do the serratus minor have?
5) How are ribs classified?

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 6) Describe anatomy and function of the diaphragm muscle
Space for your answers