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THORAX
Thoracic nerves
Blood supply
Joints of thoracic wall
Mechanism of breathing
BAAB 02/05/2016
THORACIC NERVES
• The thoracic nerves refer to the cluster of spinal nerve
fibers found in the upper body particularly within the
chest region (thorax).
• The nerves carry and transmit information between the
spinal cord and parts of the thorax
• The nerves stem from portions of the vertebrae.
• Eleven of the 12 nerves are situated in intercostal
spaces (located between two ribs) and are called
intercostal nerves.
• The last thoracic nerve, known as subcostal, is found
just below the 12th rib.
• In general, these nerves communicate with various
parts of the chest and abdomen.
Thoracic nerves cont………
Thoracic nerves cont………
• The fibers of the first two thoracic nerves extend
to the shoulder and arms (ref to the brachial
plexus).
• The next four nerves direct signals to the chest.
• The lower five thoracic nerves are found in the
chest and abdomen. The eleventh is called
thoracicoabdominal intercostal nerves
• The last thoracic nerve (twelfth) supplies the
abdominal wall and the buttocks, specifically the
skin.
• The 7th intercostal nerve terminates at the
xyphoid process, at the lower end of the sternum.
• The 10th intercostal nerve terminates at the navel.
Thoracic nerves cont………
• Each of the thoracic nerves is divided into anterior
and posterior branches known as the dorsal and
ventral ramus respectively.
• These fiber extensions direct signals to various parts
of the thorax including muscles, deep tissues, skin,
and blood vessels.
• The intercostal nerves are musculoskeletocutenous
in nature by their branches. Muscular branches supply
Intercostales, the Subcostales, the Levatores
costarum, the Serratus posterior superior, and the
Transversus thoracis. At the front of the thorax some
of these branches cross the costal cartilages from one
intercostal space to another.
• Cutenous branches are distributed all over the
thoracis skin and partly over the abdominal skin
Thoracic nerves cont………
Thoracic nerves cont………
• Lateral cutaneous branches are derived from
the intercostal nerves, about midway between the
vertebræ and sternum; they pierce the
Intercostales externi and Serratus anterior, and
divide into anterior and posterior branches.
• The anterior branches run forward to the side
and the forepart of the chest, supplying the skin
and the mamma; those of the fifth and sixth
nerves supply the upper digitations of the
Obliquus externus abdominis.
• The posterior branches run backward, and
supply the skin over the scapula and Latissimus
dorsi
Thoracic nerves cont………
• The lateral cutaneous branch of the second intercostal
nerve does not divide, like the others, into an anterior
and a posterior branch; it is named the
intercostobrachial nerve.
• The lateral cutaneous branch of the last (twelfth)
thoracic nerve is large, and undivided.
• It perforates the internal and the external oblique
muscles, descends over the iliac crest in front of the
lateral cutaneous branch of the iliohypogastric nerve,
and is distributed to the skin of the front part of the
gluteal muscles, some of its filaments extending as low
as the greater trochanter of the femur.
Thoracic nerves cont………
• the intercostal nerves arise from the somatic
nervous system. This enables them to control
the contraction of muscles, as well as provide
specific sensory information regarding the skin
and parietal pleura.
• Visceral pleura is innervate by the nerves from
the autonomic nervous system
• Damage to the internal wall of the thoracic
cavity can be felt as a sharp pain localized in
the injured region.
• Damage to the visceral pleura is experienced
as an un-localized ache.
Thoracic nerves cont………
Thoracic nerves cont………
• Long thoracic nerve:
– This arises from the anterior rami of C5- C7
(occassionaly C7 is absent) brachial plexus and
supply the serratus anterior.
• Phrenic nerve:
– This nerve arises from C3-C5. mainly it arises from
C4 which receives contributions from C3 and C5. It
descends through the neck and between the lungs
and the heart to supply the diaphragm.
Thoracic nerves cont………
The Brachial Plexus:
BLOOD SUPPLY
• The Aorta:
– The aorta is the main artery in the human body,
originating from the left ventricle of the heart and
extending down to the abdomen, where it splits into
two smaller arteries (the common iliac arteries).
– The aorta distributes oxygenated blood to all parts of
the body through the systemic circulation.
– Course of the aorta in the thorax (anterior view),
starting posterior to the main pulmonary artery, then
anterior to the right pulmonary arteries, the trachea and
the esophagus, then turning posteriorly to course
dorsally to these structures.
Blood supply cont…..
Blood supply cont…..
• In anatomical sources, the aorta is usually
divided into sections
• One way of classifying a part of the aorta is by
anatomical compartment, where
– the thoracic aorta (or thoracic portion of the aorta)
runs from the heart to the diaphragm.
– The aorta then continues downward as the
abdominal aorta (or abdominal portion of the
aorta)through the diaphragm to the aortic
bifurcation.
Blood supply cont…..
• Another system divides the aorta with respect to
its course and the direction of blood flow.
– In this system, the aorta starts as the ascending aorta
then travels superiorly from the heart and then makes a
hairpin turn known as the aortic arch.
– From the aortic arch, the aorta travels inferiorly as the
descending aorta.
– The descending aorta has two parts. The aorta begins
to descend in the thoracic cavity, and consequently is
known as the thoracic aorta.
– After the aorta passes through the diaphragm, it is
known as the abdominal aorta.
– The aorta ends by dividing into two major blood
vessels, the common iliac arteries and a smaller
midline vessel, the median sacral artery.
Blood supply cont…..
• Ascending aorta
• The ascending aorta begins at the opening of the
aortic valve in the left ventricle of the heart.
– It runs through a common pericardial sheath with the
pulmonary trunk. These two blood vessels twist around
each other, causing the aorta to start out posterior to the
pulmonary trunk, but end by twisting to its right and
anterior side.
– The transition from ascending aorta to aortic arch is at
the pericardial reflection on the aorta.
Blood supply cont…..
• At the root of the ascending aorta, the lumen has
three small pockets between the cusps of the aortic
valve and the wall of the aorta, which are called the
aortic sinuses or the sinuses of Valsalva.
– The left aortic sinus contains the origin of the left
coronary artery and the right aortic sinus likewise gives
rise to the right coronary artery. Together, these two
arteries supply the heart.
– The posterior aortic sinus does not give rise to a coronary
artery. For this reason the left, right and posterior aortic
sinuses are also called left-coronary, right-coronary and
non-coronary sinuses.
Blood supply cont…..
Aortic arch
• The aortic arch loops over the left pulmonary artery and
the bifurcation of the pulmonary trunk, to which it remains
connected by the ligamentum arteriosum, a remnant of the
fetal circulation that is obliterated a few days after birth.
• In addition to these blood vessels, the aortic arch crosses
the left main bronchus. Between the aortic arch and the
pulmonary trunk is a network of autonomic nerve fibers,
the cardiac plexus or aortic plexus.
• The left vagus nerve, which passes anterior to the aortic
arch, gives off a major branch, the recurrent laryngeal
nerve, which loops under the aortic arch just lateral to the
ligamentum arteriosum. It then runs back to the neck.
Blood supply cont…..
• The aortic arch has three major branches: from
proximal to distal, they are the brachiocephalic
trunk, the left common carotid artery, and the left
subclavian artery.
• The brachiocephalic trunk supplies the right side
of the head and neck as well as the right arm and
chest wall,
• The latter two together supply the left side of the
same regions.
• The aortic arch ends and the descending aorta
begins at the level of the intervertebral disc
between the fourth and fifth thoracic vertebrae.
Blood supply cont…..
Thoracic aorta
• The thoracic descending aorta gives rise to the intercostal and
subcostal arteries, superior and inferior left bronchial arteries
and variable branches to the esophagus, mediastinum, and
pericardium.
• Its lowest pair of branches are the superior phrenic arteries,
which supply the diaphragm, and the subcostal arteries for the
twelfth rib.
Abdominal aorta
• The abdominal aorta gives rise to lumbar and musculophrenic
arteries, renal and middle suprarenal arteries, and visceral
arteries (the celiac trunk, the superior mesenteric artery and the
inferior mesenteric artery). It ends in a bifurcation into the left
and right common iliac arteries. At the point of the bifurcation,
there also springs a smaller branch, the median sacral artery.
Blood supply cont…..
Arteries of the Thorax:
• The thoracic region of the body showcases the
remarkable complexity of human anatomy
• blood vessels in this critical region enable sensation and
allow blood to flow throughout the entire body.
• Anterior intercostal arteries: The first six anterior
intercostal arteries stem directly from the internal
thoracic artery. The rest of them branch off the
musculophrenic artery.
• Posterior intercostal arteries: Two of these arteries
branch off the superior intercostal artery in the first two
intercostal spaces, and the remaining posterior
intercostal arteries are branches of the descending
thoracic aorta.
Blood supply cont…..
Bones and Joints in the Thoracic Region
Bones and Joints…..
• The thoracic cage is made up of bones and
cartilage along with joints and an assortment
of muscles and other soft tissues
• It has the superior and inferior apertures
• the bottom of the thoracic cage (the inferior
thoracic aperture) is closed by a muscle called
the diaphragm.
• Its main function is to protect your heart,
lungs, and major blood vessels located inside.
Bones and Joints…..
• The bones that create the architecture of the
thoracic cage include the sternum, the ribs, and
the thoracic vertebrae.
• The sternum: The sternum is a flat, long bone
that forms the medial and anterior part of the
thoracic cage. It has three parts:
– Manubrium: The manubrium forms the upper part of
the sternum. It articulates with the clavicles and
attaches to the cartilage of the first two ribs. Joints are
sternoclavicular and sternocostal joints
– Body: This part has segments called sternobrae. It
articulates with the costal cartilages of the 2nd through
7th ribs on its sides and with the xiphoid process. The
joint is xiphisternal and sternocostal joint.
– Xiphoid process: This small piece of cartilage turns
into bone during adulthood. It’s located at the inferior
end of the sternal body at the xiphisternal joint.
Bones and Joints…..
• The ribs: Are 12 pairs (left and right) of flat, curved
bones that give the thoracic cage its shape. They
articulate with the thoracic vertebrae in your back,
and most of them are attached directly or indirectly
to your sternum by costal cartilages. Three types
are
– i. Vertebrosternal ribs, ii. Vertebrochondral ribs
iii. Vertebral ribs
• These cartilages help hold the thoracic cage to the
sternum and add elasticity to the thoracic cage.
• Each rib is separated from neighboring ribs by an
intercostal space that runs between the ribs along
their full lengths. The space below the 12th rib is
called the subcostal space.
Bones and Joints…..
The thoracic joints
• The cartilaginous joints in your thoracic cage allow you
to breath.
• The 1st ribs don’t move at all, but the act of breathing
requires the other ribs to move up and down a bit, so
the joints formed between the rest of the ribs and
thoracic vertebrae allow some movements.
• These joints are:
– Vertebrocostal joints (12 pairs) btn vertebral bones and
the ribs
– Strenocosto joints (6 pairs) btn the sternum and the ribs
– Costochondral joints (4 pairs) btn the ribs and the
corresponding cartilage bars which connects to the sternum
Bones and Joints…..
• Manubriosternal joint: The joint between the
manubrium and the body of the sternum; forms the
sternal angle
• Xiphisternal joint: Formed between the sternal body
and xiphoid process
• Costovertebral joints: Formed between the heads of
the ribs and the bodies of the vertebrae and the necks of
the ribs and the transverse processes of the vertebrae
• Sternocostal joints: Join the sternum to the costal
cartilages
• Sternoclavicular joints: Join the sternum and clavicles
• Costochondral joints: Attach the ribs to the costal
cartilages
• Interchondral joints: Join cartilage to cartilage
The Mechanics of Breathing
• The action of breathing in and out is due to
changes of pressure within the thorax, in
comparison with the outside (external
respiration)
• When we inhale the intercostal muscles (between
the ribs) and diaphragm contract to expand the
chest cavity.
• The diaphragm flattens and moves downwards
and the intercostal muscles move the rib cage
upwards and out
• This increase in size decreases the internal air
pressure and so air from the outside (at a now
higher pressure that inside the thorax) rushes into
the lungs to equalise the pressures.
Breathing……
• When we exhale the diaphragm and intercostal muscles
relax to resting positions. This reduces the size of the
thoracic cavity, thereby increasing the pressure and forcing
air out of the lungs.
• Breathing Rate
• The inhalation and exhalation rates are controlled by the
respiratory centre, within the Medulla Oblongata in the
brain.
– Inspiration occurs due to increased firing of inspiratory nerves
and so the increased recruitment of motor units within the
intercostals and diaphragm.
– Exhalation occurs due to a sudden stop in impulses along the
inspiratory nerves.
• Our lungs are prevented from excess inspiration due to
stretch receptors within the bronchi and bronchioles which
send impulses to the Medulla Oblongata when stimulated
Breathing……
• Also breathing rate is all controlled by
chemoreceptors within the main arteries which
monitor the levels of Oxygen and Carbon Dioxide
within the blood.
 If oxygen saturation falls, ventilation accelerates to increase
the volume of Oxygen inspired.
• If levels of Carbon Dioxide increase a
substance known as carbonic acid is released
into the blood which causes Hydrogen ions
(H+) to be formed.
 An increased concentration of H+ in the blood
stimulates increased ventilation rates. This also
occurs when lactic acid is released into the blood
following high intensity exercise.
Breathing……
• Both inhalation and exhalation (respiration)depend on
pressure gradients between the lungs and atmosphere,
as well as the muscles in the thoracic cavity.
• The mechanics of breathing follow Boyle's Law
which states that pressure and volume have an inverse
relationship
Breathing……
• The relationship between gas pressure and volume helps to
explain the mechanics of breathing.
Boyles law
This graph of data from Boyle's original 1662 experiment shows that pressure and volume are inversely related. No units
Breathing……
The process of exhalation occurs due to an elastic recoil of the lung
tissue which causes a decrease in volume, resulting in increased
pressure in comparison to the atmosphere; thus, air rushes out of
the airway.
Inhalation and exhalation
Breathing……
There is no contraction of muscles during exhalation; it
is considered a passive process.
Each lung is surrounded by an invaginated sac
The lung is protected by layers of tissue referred to as
the visceral pleura and parietal pleura; the intrapleural
space contains a small amount of fluid that protects the
tissue by reducing friction.
If these layers of tissues become inflamed, this is
categorized as pleurisy: a painful inflammation that
increases the pressure within the thoracic cavity,
reducing the volume of the lung.