Download THE THORACIC CAGE

THE THORACIC
CAGE
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The thoracic cage is a osseo-cartilaginous,
elastic & a conical cavity.
It has a inlet & a outlet.
Inlet is narrowers
outlet is broader.
The cage is flatened anteroposteriorly & on
cross-section is reniform in shape. However, in
the new born , it is rounded on cross-section.
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BOUNDARIES
Behind
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the bodies of 12 thoracic vertebra & their
intervertebral discs.
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transverse processes of the vertebrae.
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Posterior parts of ribs extending upto the
posterior angles
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Front
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Strenum
- which consists of the manubrium, body & xiphoid
process
- the manubrium lies opposite the bodies of T3 &
T4
- sternal body lies opposite T5 & T8
- sternal angle correspond to the lower border of
T4
- xiphi-sternal joint correspond with the
intervertebral disc between T8 & T9.
Anterior part of the ribs & their costal cartilages.
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On each side
Twelve ribs & their costal cartilages separated by
intercostal spaces,
front.
- the last two spaces being open in
- the intercostal spaces are occupied
by the intercostal muscles, vessels & nerves.
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INLET OF THORAX
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it is reniform in shape.
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It measures 5cms antero-posterior & 10 cms in
transverse diameters.
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inlet slopes downwards &forwards.
The sternal end of the first rib lies 3 to 4 cms lower
than the verterbral end.
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Bounded behind by the body of T1, at the sides by
the first rib & its cartilage; in front by the upper border
of the manubrium.
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OUTLET OF THORAX
It is bounded
- behind by the body of T12.
- In the front by the 7,8,9 & 10th costal
cartilages & the xiphoid process forming an
infra sternal angle.
- At the sides by the 11 & 12 th ribs.
The outlet is closed by the diaphragm.
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FUNCTIONS OF THE THORACIC CAVITY
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It contains & protects essential organs of
respiration & circulation ( lungs & heart )
It alters the diameters of the thorax during
the different phases of respiration – by the
movement of the ribs & the diaphragm.
Some of the sub-diaphragmatic organs like
liver, stomach & spleen are placed beneath
the costal margins.
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STERNAL ANGLE
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It forms a important land mark for counting the ribs. –
the sternal angle articulate with the 2nd costal
cartilage.
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it is the junction between the superior & inferior
mediastinum.
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Sternum moves at tha sterno-manubrial joint during
respiration.
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Trachea bifurcates close to this level.
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Beginning & ending of the arch of aorta.
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Thoracic duct deviates from right to the left
behind the oesophagus at this level.
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Superior venacava pierces the fibrous
pericardium.
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Arch of the azygos vein terminates here.
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Anterior margins of the lungs & the pleura
approximate at the sternal angle.
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INTERCOSTAL SPACE
There are eleven intercostal spaces on each
side.
Last two are open in the front because the
11th & the 12th ribs are floating ribs.
Those spaces intervening between the typical
ribs & traversed by vessels & nerves are known
as the typical inter-costal spaces.
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The 3rd ,4th, 5th & 6th intercostal spaces are the
typical inter costal spaces & possess the
following boundaries :
above : sharp lower margin of the rib above
& its cartilage.
below : blunt upper border of the rib below &
its costal cartilage.
in front : lateral margin of the sternum
behind : body of the corresponding thoracic
vertebra.
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Posterior part of each space is placed between
two ribs is called the inter-osseous part.
Anterior part intervening between the two
cartilages is called the inter-cartilaginous part.
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CONTENTS
1)
- INTERCOSTAL MUSCLES.
2)
- INTERCOSTAL VESSELS.
3)
- INTERCOSTAL NERVES.
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INTERCOSTAL MUSCLES.
The muscles are arranged in three layers from
outside inwards –
- Intercostalis Externus
- Intercostalis Internus
- Intercostalis Intimus (inner
most inter-costal muscle)
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Intercostalis externus
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it extends from the sternum to the tubercles of
the ribs.
in the inter-osseous part it is fleshy
in the inter-cartilagenous part it is replaced by
an aponeurosis known as the anterior
intercostal membrane.
The fibres are directed downwards, forwards &
medially in the anterior part.
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Origin :
it arises from the lower border of the
upper rib .
Insertion :
it is inserted into the outer lip of the upper
border of the lower rib.
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Intercostalis internus
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It extends from the sternum to the posterior
angels of the ribs.
The anterior part is fleshy.
Posteriorly, it is replaced by the posterior
intercostal membrane.
The direction of the fibres are at right angles to
that of the externus muscle.
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Origin :
rib.
it arises from the costal groove of the upper
Insertion:
into the intermediate part of the upper
border of the lower rib.
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INTERCOSTALIS INTIMUS.
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It is a part of the transversus thoracis muscle.
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It occupies middle 2/4 of the intercostal space.
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The intercostal nerves & the vessels run in
between the internus & intimus muscles –
called the neurovascular plane.
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ORIGIN :
it arises from the upper lip of the
costal groove of the rib above
INSERTION:
into the inner lip of the upper border
of the rib below.
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TRANSVERSE THORACIS MUSCLE
it has three components
- sub costalis
- intercostalis intimus
- sternocostalis.
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Action of the muscles
External intercostal : elevates the ribs.
Helps in inspiration
Internal intercostal :depress the ribs
Helps in expiration.
They prevent blowing out or sucking in of the
intercostal spaces during respiration
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INTERCOSTAL VESSELS.
ARTERIES
In each space there are TWO groups
- anterior
- posterior.
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ANTERIOR INTERCOSTAL ARTERIES
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Present in all spaces expect in the last two spaces.
In each space they are two in number.
One follows the upper margin & other follows the
lower margin of the intercostal space.
They run in the neurovascular plane.
They anastomose with the posterior intercostal
arteries at the junction of the ant 1/3 & post 2/3 of the
space.
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In the upper six spaces they are the branches of
the internal thoracic artery.
In the lower three spaces they are derived from
the musculo -phrenic artery.
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POSTERIOR INTERCOSTAL ARTERIES
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Each space is occupied by one posterior
intercostal artery
In the upper two spaces they are the branches
of the superior intercostal artery – from the
costocervical trunk of the subclavian artery.
In the lower 9 spaces they are the branches of
the descending thoracic aorta.
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Neurovascular groove
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The intercostal nerves & the vessels run in
between the internus & intimus muscles called
the neurovascular plane.
In the neurovascular groove, the arrangement
of the structures are (from above downwards):
VAN - vein
- artery
- nerve
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INTERCOSTAL VEINS
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Corresponds to the arteries
Arranged in two groups
- anterior
- posterior.
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Anterior group –
upper six spaces drain into internal thoracic
vein
lower spaces drain into the musculo-phrenic
vein.
Posterior group –
Each space presents one posterior vein.
They terminates in different manner on two
sides
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INTERCOSTAL NERVES
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Eleven in number in each side.
Each nerve is the ventral ramus of a thoracic
nerve.
3rd to 6th nerves are typical
7th to 11th nerves appear in the anterior
abdominal wall.
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Course
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The nerves pass through the respective intervertebral
foramen & appears in the posterior part of the space.
It intervenes in the endothoracic fascia, between the
costal pleura & posterior intercostal membrane.
On reaching the angle of the upper rib, it gives off a
collateral branch & a lateral cutaneous branch.
Then, it passes along the costal groove , in the
neurovascular plane.
In the anterior part of the space , it passes in front of
the sternocostalis muscle ,crosses internal thoracic
artery, pierces intercostalis internus, anterior
intercostal membrane, pectoralis major
Terminates as the anterior cutaneous nerve.
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Branches
DISTRIBUTING BRANCHES
 Collateral branch
 Lateral cutaneous branches –pierces the internus &
the externus muscles in the midaxillary line. Divides
in to anterior & posterior branches.
COMMUNICATING BRANCHES
 Ganglionic branches – with the sympathetic
Ganglion, via the grey & white rami communicantes.
 In the anterior ppart of the space , they communicate
with the adjacent nerves behind the costal
cartilages.
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APPLIED ANATOMY
INTER COSTAL NEURALGIA
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A sharp burning pain in the area of the skin
supplied by thoracic spinal nerves.
It may be produced by the rib fractures.
The important cause of neuralgia is HERPES
ZOSTER which is a viral disease of the spinal
ganglia.– vesicular eruptions appear along the
dermatomes of the affected nerves.
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RESPIRATORY MOVEMENTS
Respiratory movements involves
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Inspiration:
muscles of inspiration are diaphragm,
intercostal muscles , erector spinae, scalene
muscles &sternocledomastoid
expiration:
expiration is a passive movement.
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MECHANISM OF RESPIRATION
During inspiration all the three diameters of the
thorax are increased
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The antero-posterior diameter– by the pump
handle movement.
The vertical diameter – by the descent of the
diaphragm producing the piston movement.
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 The
transverse diameter -- by the passive&
active methods.
- the passive method is found in the
upper 6 ribs
- the active method is seen in 7th to 11th
ribs by the bucket handle movement
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