Muscles of the thorax pdf - Thorax

(see Fig. 2.16).

stomach contents into the thoracic part of the esophagus

and possibly assist in the prevention of regurgitation of the

a slinglike loop. These fibers appear to act as a sphincter

pass up to the left and surround the esophageal orifice in

pericardium. Some of the muscle fibers of the right crus

don is partially fused with the inferior surface of the fibrous

is shaped like three leaves. The superior surface of the ten

which

central tendon,

The diaphragm is inserted into a

crosses over the anterior surface of the aorta (see Fig. 2.16).

which

median arcuate ligament,

crura are connected by a

lower border of the 12th rib. The medial borders of the two

of the transverse process of the first lumbar vertebra to the

vertebra. The lateral arcuate ligament extends from the tip

vertebra to the tip of the transverse process of the first lumbar

ment extends from the side of the body of the second lumbar

(see Fig. 2.16). The medial arcuate liga

arcuate ligaments

lateral

medial

the crura the diaphragm arises from the

vertebrae and the intervertebral disc (see Fig. 2.16). Lateral to

arises from the sides of the bodies of the first two lumbar

crus

left

three lumbar vertebrae and the intervertebral discs; the

arises from the sides of the bodies of the first

right crus

The

from the arcuate ligaments

arising by vertical columns or crura and

vertebral part

ribs and their costal cartilages (see Fig. 2.16)

arising from the deep surfaces of the lower six

costal part

xiphoid process (see Fig. 2.2)

arising from the posterior surface of the

sternal part

origin of the diaphragm can be divided into three parts:

opening, and a centrally placed tendon (see Fig. 2.16). The

cular part, which arises from the margins of the thoracic

tion. It is dome shaped and consists of a peripheral mus

The diaphragm is the most important muscle of respira

pass between the chest and the abdomen.

cavity below (Fig. 2.16). It is pierced by the structures that

that separates the chest cavity above from the abdominal

The diaphragm is a thin muscular and tendinous septum

The Thorax: Part I—The Thoracic Wall

Diaphragm

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-

and

Traumatic Injury to the Thorax

When the anatomy of the thorax is reviewed, it is important to

ula, which overlies the upper seven ribs. This bone is covered

of a vertebral fracture with associated injury to the spinal cord

tebral column. In severe posterior chest injuries, the possibility

is sucked in during inspiration and driven out during expiration,

case, the stability of the chest wall is lost, and the flail segment

either side of the sternum, the sternum may be flail. In either

nected to the rest of the thoracic wall. If the fractures occur on

and anteriorly near the costochondral junctions. This causes

ited to one side, the fractures may occur near the rib angles

patient to breathe adequately, it may be necessary to relieve the

Severe localized pain is usually the most important symptom

jagged ends of a fractured rib may penetrate the lungs and pres

and the delicate pleura internally, it is not surprising that the

Because the rib is sandwiched between the skin externally

posteriorly. The 11th and 12th ribs float and move with the force of

muscles anteriorly and by the scapula and its associated muscles

ribs. The first four ribs are protected by the clavicle and pectoral

tively fixed. Ribs 5 through 10 are the most commonly fractured

may be injured. With increasing age, the rib cage becomes more

can be easily compressed so that the underlying lungs and heart

Fractures of the ribs are common chest injuries. In children,

Traumatic injury to the thorax is common, especially as a result

of automobile accidents.

Fractured Sternum
The sternum is a resilient structure that is held in position by

relatively pliable costal cartilages and bendable ribs. For these

reasons, fracture of the sternum is not common; however, it does

occur in high-speed motor vehicle accidents. Remember that the

heart lies posterior to the sternum and may be severely contused

by the sternum on impact.

Rib Contusion
Bruising of a rib, secondary to trauma, is the most common

rib injury. In this painful condition, a small hemorrhage occurs

beneath the periosteum.

Rib Fractures

the ribs are highly elastic, and fractures in this age group are

therefore rare. Unfortunately, the pliable chest wall in the young

rigid, owing to the deposit of calcium in the costal cartilages, and

the ribs become brittle. The ribs then tend to break at their weak-

est part, their angles.

The ribs prone to fracture are those that are exposed or rela-

impact.

ent as a pneumothorax.

of a fractured rib. The periosteum of each rib is innervated by the

intercostal nerves above and below the rib. To encourage the

pain by performing an intercostal nerve block.

Flail Chest
In severe crush injuries, a number of ribs may break. If lim-

flail chest, in which a section of the chest wall is discon-

producing paradoxical and ineffective respiratory movements.

Traumatic Injury to the Back of the Chest

The posterior wall of the chest in the midline is formed by the ver-

should be considered. Remember also the presence of the scap-

with muscles and is fractured only in cases of severe trauma.

Traumatic Injury to the Abdominal Viscera

and the Chest

remember that the upper abdominal organs—namely, the liver,

stomach, and spleen—may be injured by trauma to the rib cage.

In fact, any injury to the chest below the level of the nipple line

may involve abdominal organs as well as chest organs.

C L I N I C A L N O T E S

Basic Anatomy

the heart. Lymph within the abdominal lymph vessels is

vena cava and forces it upward into the right atrium of

pressure change compresses the blood in the inferior

same time increases the intra-abdominal pressure. This

phragm decreases the intrathoracic pressure and at the

The descent of the dia

Thoracoabdominal pump:

the bladder and anal canal under these circumstances.

it is important to have adequate sphincteric control of

muscles in the lifting of heavy weights. Needless to say,

prevent flexion. This greatly assists the postvertebral

extent that it helps support the vertebral column and

wall in raising the intra-abdominal pressure to such an

phragm assists the muscles of the anterior abdominal

breath and holding it (fixing the diaphragm), the dia

In a person taking a deep

Weight-lifting muscle:

escape, producing a grunting sound.

in the respiratory tract. Now and again, air is allowed to

diaphragm is unable to rise because of the air trapped

a deep breath and closing the glottis of the larynx. The

This mechanism is further aided by the person taking

pressure for micturition, defecation, and parturition.

anterior abdominal wall in raising the intra-abdominal

diaphragm assists the contraction of the muscles of the

The contraction of the

Muscle of abdominal straining:

important muscle used in inspiration.

cal diameter of the thorax. The diaphragm is the most

pulls its central tendon down and increases the verti

On contraction, the diaphragm

Muscle of inspiration:

Functions of the Diaphragm

don and increases the vertical diameter of the thorax.

On contraction, the diaphragm pulls down its central ten

Action of the Diaphragm

from the lower six intercostal nerves.

the phrenic nerve and the periphery of the diaphragm is

covering the central surfaces of the diaphragm are from

The parietal pleura and peritoneum

Sensory nerve supply:

(C3, 4, 5).

The right and left phrenic nerves

Motor nerve supply:

Nerve Supply of the Diaphragm

the xiphoid process (see Fig. 2.2).

vertebral column and the short limb extending forward to

ance of an inverted J, the long limb extending up from the

When seen from the side, the diaphragm has the appear

ing; it is higher in the supine position and after a large meal.

The diaphragm is lower when a person is sitting or stand

ture, and the degree of distention of the abdominal viscera.

the diaphragm vary with the phase of respiration, the pos

whereas the central tendon supports the heart. The levels of

sternal joint. The domes support the right and left lungs,

the liver.) The central tendon lies at the level of the xiphi

at a higher level, because of the large size of the right lobe of

reach the lower border of the 5th rib. (The right dome lies

as the upper border of the 5th rib, and the left dome may

or cupulae. The right dome reaches as high

and left domes,

right

As seen from in front, the diaphragm curves up into

Shape of the Diaphragm

■

Needle Thoracostomy

right). Avoid damaging the diaphragm and entering the perito

the lower intercostal spaces is possible provided that the pres

the bundle passes forward to the rib angle, it becomes closely

The preferred insertion site for a tube thoracostomy is the fourth

(d) external intercostal muscle, (e) internal intercostal muscle, (f)

toral muscles are then penetrated), (c) serratus anterior muscle,

ing structures as it passes through the chest wall (see Fig. 2.8):

The skin is prepared in the usual way, and a local anesthetic

the 2nd rib, and the second intercostal space are found in the

For the anterior approach, the patient is in the supine position.

drain fluid (blood or pus) away from the pleural cavity to allow

A needle thoracostomy is necessary in patients with tension

pneumothorax (air in the pleural cavity under pressure) or to

the lung to reexpand. It may also be necessary to withdraw a

sample of pleural fluid for microbiologic examination.

Anterior Approach

The sternal angle is identified, and then the 2nd costal cartilage,

midclavicular line.

Lateral Approach
For the lateral approach, the patient is lying on the lateral side.

The 2nd intercostal space is identified as above, but the anterior

axillary line is used.

is introduced along the course of the needle above the upper bor-

der of the 3rd rib. The thoracostomy needle will pierce the follow-

(a) skin, (b) superficial fascia (in the anterior approach the pec-

innermost intercostal muscle, (g) endothoracic fascia, and (h) pari-

etal pleura.

The needle should be kept close to the upper border of the

3rd rib to avoid injuring the intercostal vessels and nerve in the

subcostal groove.

Tube Thoracostomy

or fifth intercostal space at the anterior axillary line (Fig. 2.14).

The tube is introduced through a small incision. The neurovas-

cular bundle changes its relationship to the ribs as it passes for-

ward in the intercostal space. In the most posterior part of the

space, the bundle lies in the middle of the intercostal space. As

related to the lower border of the rib above and maintains that

position as it courses forward.

The introduction of a thoracostomy tube or needle through

ence of the domes of the diaphragm is remembered as they

curve upward into the rib cage as far as the 5th rib (higher on the

neal cavity and injuring the liver, spleen, or stomach.

C L I N I C A L N O T E S

(continued)

first part of the subclavian artery in the neck. It descends

body from the clavicle to the umbilicus. It is a branch of the

The internal thoracic artery supplies the anterior wall of the

tal origins of the diaphragm on each side (see Fig. 2.16).

superior epigastric vessels pass between the sternal and cos

terior to the medial arcuate ligament on each side; and the

nerves pierce the crura; the sympathetic trunks pass pos

In addition to these openings, the sympathetic splanchnic

right phrenic nerve.

mits the inferior vena cava and terminal branches of the

vertebra in the central tendon (see Fig. 2.16). It trans

lies at the level of the 8th thoracic

caval opening

The

third of the esophagus.

the left gastric vessels, and the lymphatics from the lower

right and left vagus nerves, the esophageal branches of

right crus (see Fig. 2.16). It transmits the esophagus, the

racic vertebra in a sling of muscle fibers derived from the

lies at the level of the 10th tho

esophageal opening

The

transmits the aorta, the thoracic duct, and the azygos vein.

thoracic vertebra between the crura (see Fig. 2.16). It

lies anterior to the body of the 12th

aortic opening

The

The diaphragm has three main openings:

backflow.

The presence of valves within the thoracic duct prevents

racic duct is aided by the negative intrathoracic pressure.

also compressed, and its passage upward within the tho

The Thorax: Part I—The Thoracic Wall

Openings in the Diaphragm

■

Internal Thoracic Artery

vertically on the pleura behind the costal cartilages, a
fingerbreadth lateral to the sternum, and ends in the sixth

verse process and is inserted into the rib below.

lar in shape and arises by its apex from the tip of the trans

There are 12 pairs of muscles. Each levator costa is triangu

each side.

racic artery and drains into the brachiocephalic vein on

The internal thoracic vein accompanies the internal tho

Internal Thoracic Vein

intercostal spaces and the diaphragm

costal margin of the diaphragm and supplies the lower

which runs around the

musculophrenic artery,

The

rectus muscle as far as the umbilicus

sheath of the anterior abdominal wall and supplies the

which enters the rectus

superior epigastric artery,

The

mediastinum (e.g., the thymus)

to the contents of the anterior

Mediastinal arteries

the phrenic nerve and supplies the pericardium

which accompanies

pericardiacophrenic artery,

The

branches of the corresponding intercostal nerves

which accompany the terminal

Perforating arteries,

costal spaces

for the upper six inter

anterior intercostal arteries

Two

Branches

and musculophrenic arteries (see Figs. 2.9 and 2.10).

intercostal space by dividing into the superior epigastric

■

Levatores Costarum

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Thoracotomy

to the diaphragm until proved otherwise. The arching domes of

circumstances, the nerve to the subclavius muscle must also

To obtain complete paralysis under these

sory phrenic nerve.

cal spinal nerve joins the phrenic nerve late as a branch from

when the physician wishes to rest the lower lobe of the lung

essary in the treatment of certain forms of lung tuberculosis,

A single dome of the diaphragm may be paralyzed by crushing

however, be a symptom of disease such as pleurisy, peritonitis,

Hiccup is the involuntary spasmodic contraction of the dia

intercostal muscle, (g) endothoracic fascia, and (h) parietal

costal membrane, (e) internal intercostal muscle, (f) innermost

side. The following tissues will be incised (see Fig. 2.14): (a)

heart and the aorta, the chest should be entered from the left

left incision depends on the site of the injury. For access to the

the anterior axillary line (Fig. 2.15). Whether to make a right or

tal space, extending from the lateral margin of the sternum to

ing procedure. After preparing the skin in the usual way, the

In patients with penetrating chest wounds with uncontrolled

intrathoracic hemorrhage, thoracotomy may be a life-sav-

physician makes an incision over the fourth or fifth intercos-

skin, (b) subcutaneous tissue, (c) serratus anterior and pecto-

ral muscles, (d) external intercostal muscle and anterior inter-

pleura.

Avoid the internal thoracic artery, which runs vertically

downward behind the costal cartilages about a fingerbreadth

lateral to the margin of the sternum, and the intercostal vessels

and nerve, which extend forward in the subcostal groove in the

upper part of the intercostal space (see Fig. 2.14).

Hiccup

phragm 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,

pericarditis, or uremia.

Paralysis of the Diaphragm

or sectioning of the phrenic nerve in the neck. This may be nec-

on one side. Occasionally, the contribution from the fifth cervi-

the nerve to the subclavius muscle. This is known as the acces-

be sectioned.

Penetrating Injuries of the Diaphragm

Penetrating injuries can result from stab or bullet wounds to the

chest or abdomen. Any penetrating wound to the chest below

the level of the nipples should be suspected of causing damage

the diaphragm can reach the level of the 5th rib (the right dome

can reach a higher level).

Basic Anatomy

intercostal vein

intercostal artery

intercostal nerve

tube

superficial fascia

serratus anterior

external
intercostal

internal intercostal

innermost intercostal

parietal pleura

pleural cavity (space)

visceral pleura

lung

skin

FIGURE 2.14

Tube thoracostomy.

and their actions is given in Table 2.1.

A summary of the muscles of the thorax, their nerve supply,

Intercostal nerves.

Nerve supply:

tory muscle.

It depresses the ribs and is therefore an expira

Action:

the lower ribs.

Its fibers pass upward and laterally and are inserted into

arises from the upper lumbar and lower thoracic spines.

The serratus posterior inferior is a thin, flat muscle that

Intercostal nerves.

Nerve supply:

muscle.

It elevates the ribs and is therefore an inspiratory

Action:

the upper ribs.

Its fibers pass downward and laterally and are inserted into

arises from the lower cervical and upper thoracic spines.

The serratus posterior superior is a thin, flat muscle that

Posterior rami of thoracic spinal nerves.

Nerve supply:

inspiratory muscle.

Each raises the rib below and is therefore an

Action:

The tube advancing

space is kept close to the upper border of the rib to avoid injuring the intercostal vessels and nerve.

and later the tube as they pass through the chest wall to enter the pleural cavity (space). The incision through the intercostal

The various layers of tissue penetrated by the scalpel

made over the intercostal space one below the space to be pierced.

The site for insertion of the tube at the anterior axillary line. The skin incision is usually

superiorly and posteriorly in the pleural space.

■

Serratus Posterior Superior Muscle

■

Serratus Posterior Inferior Muscle

■

The Thorax: Part I—The Thoracic Wall

neck

line of

incision

pectoralis

minor

pectoralis

major

left lung

diaphragm

pericardium

anterior intercostal

membrane

external intercostal

muscle

left phrenic nerve

serratus
anterior

latissimus
dorsi

long thoracic

nerve

FIGURE 2.15

Left thoracotomy.

the way to visualize the mediastinum.

phrenic nerve descends over the pericardium beneath the mediastinal pleura. The collapsed left lung must be pushed out of

The pleural space opened and the left side of the mediastinum exposed. The left

injuring the intercostal vessels and nerve.

ated muscles. The line of incision through the intercostal space should be placed close to the upper border of the rib to avoid

The exposed ribs and associ

Site of skin incision over fourth or fifth intercostal space.

Basic Anatomy

right phrenic nerve

inferior vena cava

left phrenic nerve

esophagus

vagi

median arcuate ligament

medial arcuate ligament

12th rib

sympathetic trunk

psoas muscle

quadratus lumborum muscle

subcostal nerve

left crus

right crus

central tendon

lateral arcuate ligament

FIGURE 2.16

he anterior portion of the right side has been removed. Note the sternal, cos

Diaphragm as seen from below. T

tal, and vertebral origins of the muscle and the important structures that pass through it.

Tip of transverse

Very important muscle of

Name of Muscle

Origin

Insertion

Nerve Supply

Action

External intercostal

muscle (11) (fibers pass

downward and forward)

Inferior border of rib

Superior border of

rib below

Intercostal nerves

With 1st rib fixed, they raise ribs

during inspiration and thus

increase anteroposterior and

transverse diameters of thorax

Internal intercostal

muscle (11) (fibers

pass downward and

backward)

Inferior border of rib

Superior border of

rib below

Intercostal nerves

With last rib fixed by abdominal

muscles, they lower ribs during

expiration

Innermost intercostal

muscle (incomplete

layer)

Adjacent ribs

Intercostal nerves

Assists external and internal

intercostal muscles

Diaphragm (most important

muscle of respiration)

Xiphoid process;

lower six costal

cartilages, first

three lumbar

vertebrae

Central tendon

Phrenic nerve

inspiration; increases vertical

diameter of thorax by pulling

central tendon downward;

assists in raising lower ribs

Also used in abdominal straining

and weight lifting

Levatores costarum (12)

process of C7 and

T1–11 vertebrae

Rib below

Posterior rami of

thoracic spinal

nerves

Raises ribs and therefore

inspiratory muscles

Serratus posterior superior

Lower cervical and

upper thoracic

spines

Upper ribs

Intercostal nerves

Raises ribs and therefore

inspiratory muscles

Serratus posterior inferior

Upper lumbar and

lower thoracic

spines

Lower ribs

Intercostal nerves

Depresses ribs and therefore

expiratory muscles

Muscles of the Thorax

T A B L E 2 . 1