Download 10 – Muscles of the Anterior Trunk

Myology
Muscles of the Anterior
Trunk
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Gross Anatomy
Osteology of the Thorax
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Thorax
• Thorax refers to the entire chest
• Functions:
– Protect organs in chest and upper abdomen
– Provides support for bones of upper limbs
• Bony cage flattened from front to back
• Formed by:
– Sternum
– Ribs
– Costal cartilages
– Bodies of thoracic vertebrae.
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• Sternum (breastbone)
– Manubrium: upper portion
• Suprasternal (Jugular) notch: depression in the upper part of
the manubrium
• Clavicular notches: lateral sides of manubrium, for
articulation with the clavicle.
• Body: middle and largest portion
– Xiphoid: inferior and smallest portion
– Sternal angle: formed by the junction of the manubrium and
body
• Ribs
– Ribs 1-7 are true ribs: direct anterior attachment to sternum
– Ribs 8-12 are false ribs: attaches indirectly to sternum or
doesn’t attach to sternum at all
– Ribs 11-12 are floating ribs: ends of ribs do not attach to
sternum
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Palpation of the Thorax
Sternum: Supine; place your fingers on the center of the chest. Then slide
superiorly toward the jugular notch at the top. Then move your fingers
slightly lateral and palpate the sternoclavicular joints (confirm by having
your partner move their upper extremity). Return to the sternum and
palpate inferiorly onto the manubrium and body. Finally, slide your
fingers down onto the xiphoid process feeling the tip between the costal
cartilages.
Ribs: Supine; slide laterally from the sternum onto the costal cartilages.
Roll off the cartilage into the spaces between. Follow the costal
cartilages laterally on to the ribs.
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Pectoralis Major
• Pec major along with the lats are important when performing a pullup.
• Both pec major and lats are powerful muscles which attach from the
trunk to the arm.
– Synergistic to each other with respect to their arm action in that
they both adduct and medially rotate the arm
– However they are antagonistic with respect to their sagittal plan
arm actions; pec major (being anterior) flexes the arm and the
lats (being posterior) extends the arm.
• Pectoralis major has layers: clavicular fibers are most superficial
(anterior); the sternal fibers are deep to the clavicular fibers; and the
costal and abdominal fibers attach more proximally on the humerus.
• Makes up the vast majority of the “anterior axillary fold” of tissue,
which borders the armpit anteriorly.
• Can only create flexion of the arm at the shoulder joint up to 60°.
• Powerful horizontal flexor of the arm at the shoulder joint.
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Pectoralis Major
O: Clavicular Head: Medial clavicle
Sternal Head: Sternum and the upper
costal cartilages
I: Lateral lip of the bicipital groove
A: Adduction, medial rotation, and
horizontal adduction of the arm. The
clavicular head also causes flexion of
the arm. Secondarily depresses and
protracts the scapula.
**Reversed muscle action causes
elevation of the trunk, lateral
deviation, and ipsilateral rotation.
N: Medial and Lateral Pectoral nerves
Palpation: page 260
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Pectoralis Minor
• When contracting it pulls on the coracoid process and pulls
scapula in such a manner that the lateral border is pulled in
toward the lateral body wall and the medial border moves
away from posterior body wall.
– This movement is called lateral tilt.
• Rounded shoulders is a common postural condition in which
the scapulae are protracted and depressed and the humeri are
medially rotated.
– Given the pec minor’s action of both protraction and
depression, when pec minor muscles are tight, they can
contribute to this condition.
• By elevating ribs 3-5, this muscle can expand the ribcage
during inspiration (accessory muscle of inspiration)
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Pectoralis Minor
O:
Anterior borders of ribs # 3
through 5
I: Coracoid process of the scapula
A: Protracts, Depresses, and
downwardly rotates the scapula
**Reversed muscle action
includes elevation of the 3rd
through 5th ribs
N: Medial pectoral nerve
Palpation: page 264
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Subclavius
• If clavicle is fixed to the scapula, then subclavius can also
depress the scapula at the scapulocostal joint
• Many believe main function is to act as a fixator of the clavicle
during arm/shoulder movements.
• Common entrapment site for nerves of brachial plexus and
subclavian artery called costoclavicular syndrome
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Subclavius
muscle is “under” the clavicle
O: 1st rib
I: Inferior surface of the
clavicle
A: Depression of the clavicle
and Elevation of the 1st rib
N: Nerve to the subclavius from
the brachial plexus
Palpation: page 267
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External Intercostals
• Oriented in the same direction as the external oblique
abdominal muscles.
– Appear to be extensions of external obliques
• Involved in respiration
• These muscles should be addressed in any client who has a
respiratory condition.
• This is the meat which is eaten when one eats spare ribs.
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External Intercostals
O: Inferior borders of ribs 1-12
I: Superior border of the rib
below
A: Elevation of ribs 2-12
N: Intercostal nerves
Palpation: page 270
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Internal Intercostals
• Oriented in the same direction as fibers of the internal
abdominal obliques.
• Generally thinner then external intercostals.
• Involved in respiration
• There is another layer of muscles called the
innermost intercostals which are located deep to the
internal intercostals.
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Internal Intercostals
located between the ribs and internal to external intercostals
O: Superior border of the rib
below
I: Inferior border of the rib
above
A: Depresses ribs 1-11
N: Intercostal nerves
Not palpable
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Transversus Thoracis
• Superior fibers run primarily vertically but inferior fibers run
horizontally
• Located internally i.e. located within thoracic cavity
• Primary role is as a respiratory muscle.
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Transversus Thoracis
Runs transversely across the thoracic region
O: Internal surfaces of the sternum,
xiphoid and adjacent costal
cartilages
I: Internal surfaces of costal
cartilages 2-6
A: Depression of ribs 2-6
N: Intercostal nerves
Not palpable
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Diaphragm
• Separates the thoracic and abdominal cavities.
• Number of openings to allow passage of structures between
thoracic and abdominal cavities.
– Largest openings for esophagus, aorta and inferior vena
cava
• Only muscle that must contract for quiet, relaxed inspiration.
• Usually under both conscious and unconscious control.
• Innervation is phrenic nerve composed of spinal nerves
C3, 4, 5.
– “C3, 4, 5 keeps the diaphragm alive!”
• Clinically a Hiatal hernia is when part of the stomach
herniates through the diaphragm into the thoracic cavity.
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Diaphragm
O: Internal surfaces of ribcage,
sternum and spine
I: Central tendon of diaphragm
A: Increases volume of thoracic
cavity during inspiration
N: Phrenic nerve
Palpation: page 293
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Muscles of the Anterior Abdominal
Wall
• Rectus abdominis located
anteromedially
• External/internal oblique and
transversus abdominis located
anterolaterally
• All four muscles compress the
abdominal contents.
• All except transversus
abdominis can flex the trunk.
• External oblique of one side is
synergistic with internal
oblique of opposite side with
trunk rotation.
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Rectus Abdominis
• Three fibrous bands known as tendinous inscriptions transect
the rectus abdominis muscles and divide each into four
sections or boxes.
– For this reason, this muscle in a well developed person is
often known as the eight-pack muscle (it is more often
incorrectly labeled as the six-pack since six of eight
compartments are more visible.
• The two rectus sheaths which encase the rectus abdominis
meet in the midline and form the linea alba.
• When old-fashioned straight legged sit-ups are done, the
movement occurs at the hip joint and not a the spinal joints.
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Rectus Abdominis
muscle runs straight up the abdomen
O: Pubis
I: Xiphoid and cartilages of ribs
5-7
A: Bilateral contraction: Flexion of
trunk, Posterior tilt of pelvis, and
compresses the abdominal contents
Unilateral contraction: lateral
flexion of the trunk
N: Intercostal nerves, iliohypogastric,
and ilioinguinal nerves
Palpation: page 281
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External Obliques
• Located lateral to rectus abdominis
• Most powerful of the 3 layers of the anterolateral abdominal
wall
– Directly deep to external oblique is internal oblique and
deep to that is the transversus abdominis
• If you put your hands in your coat pocket, your fingers
would be pointing along the direction of this muscle.
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External Abdominal Oblique
located externally and fibers oriented obliquely
O: Anterior iliac crest; pubic bone and
abdominal aponeurosis
I: Lower 8 ribs
A: Bilateral contraction: Trunk flexion,
Posterior tilt of pelvis, and compression
of the abdominal contents.
Unilateral contraction: Lateral trunk
flexion, Contralateral trunk rotation,
and elevation of the pelvis.
N: Intercostal nerves, iliohypogastric, and
ilioinguinal nerves
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Palpation: page 284
Internal Obliques
• If you were to put your hands in your back pockets, your
fingers would be pointing along the direction of this
muscle.
• It is an ipsilateral trunk rotator and antagonistic to its
external oblique partner on the same side.
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Internal Abdominal Oblique
located internally and fibers oriented obliquely
O: Inguinal ligament, iliac crest and
thoracolumbar fascia
I: Lower 3 ribs and the abdominal
aponeurosis
A: Bilateral contraction: Trunk flexion,
Posterior tilt of pelvis, and compresses
the abdominal contents.
Unilateral contraction: Lateral trunk
flexion, Ipsilateral trunk rotation, and
elevation of the pelvis
N: Intercostal nerves, iliohypogastric,
and ilioinguinal nerves
Palpation: page 287
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Transversus Abdominis
• Is the only abdominal muscle that cannot act as a mover
of a skeletal action.
– Primary purpose is to compress the abdominal
contents.
• Upper fibers are contiguous with the diaphragm and the
transversus thoracis.
• Sometimes called the corset muscle because it wraps
around the abdomen.
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Transversus Abdominis
O: Inguinal ligament, iliac crest,
thoracolumbar fascia and lower
costal cartilages
I: Abdominal aponeurosis
A: Compression of abdominal
contents
N: Intercostal nerves,
iliohypogastric, and ilioinguinal
nerves
Palpation: page 287
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