Anterior Chest wall muscles

Question 1

Pectoralis Major

Answer 1

Attachments:
Clavicular head – originates from the anterior surface of the medial clavicle.
Sternocostal head – originates from the anterior surface of the sternum, the superior six costal cartilages and the aponeurosis of the external oblique muscle.
The distal attachment of both heads is onto the intertubercular sulcus of the humerus.

Function:
Adducts and medially rotates the upper limb and draws the scapula anteroinferiorly.
The clavicular head also acts individually to flex the upper limb.

Innervation: Lateral and medial pectoral nerves (C5-T1).

Blood supply:
pectoral branches of thoracoacromial artery and the perforating branches of internal thoracic artery.

Question 2

Pectoralis Minor

Answer 2

Origin:
Anterior surface, costal cartilages of ribs 3-5
Insertion Medial border and coracoid process of scapula

Innervation:
Medial and lateral pectoral nerves (C5-T1)

Blood supply: Thoracoacromial a. (pectoral and deltoid branches), superior thoracic a., lateral thoracic a.

Function:
Scapulothoracic joint: draws scapula anteroinferiorly, stabilizes scapula on thoracic wall

Question 3

Serratus anterior

Answer 3

Attachments:
The muscle consists of several strips, which originate from the lateral aspects of ribs 1-8. They attach to the costal (rib facing) surface of the medial border of the scapula.

Function:
Rotates the scapula, allowing the arm to be raised over 90 degrees. It also holds the scapula against the ribcage.

Innervation:
Long thoracic nerve.

Blood supply:
Superior and lateral thoracic arteries, thoracodorsal artery branches

Question 4

Subclavius

Answer 4

Attachments:
Originates from the junction of the 1st rib and its costal cartilage. It inserts onto the inferior surface of the middle third of the clavicle.

Function:
Anchors and depresses the clavicle.

Innervation:
Nerve to subclavius.

Blood supply:
Clavicular branch of thoracoacromial artery, suprascapular artery

Question 5

External intercostal

Answer 5

Attachments:
Originate at the lower border of the rib, inserting into the superior border of the rib below.

Actions:
Elevates the ribs, increasing the thoracic volume.

Innervation:
Intercostal nerves (T1-T11).

Blood supply:
Anterior and posterior intercostal arteries

Question 6

Internal intercostal

Answer 6

Attachments:
Originates from the lateral edge of the costal groove and inserts into the superior surface of the rib below.

Actions:
The interosseous part reduces the thoracic volume by depressing the ribcage, and the interchondral part elevates the ribs.

Innervation:
Intercostal nerves (T1-T11).

Blood supply:
Anterior intercostal, posterior intercostal, internal thoracic and musculophrenic arteries; costocervical trunk

Question 7

Innermost intercostal

Answer 7

Attachments:
Originates from the medial edge of the costal groove and inserts into the superior surface of the rib below.

Actions:
The interosseous part reduces the thoracic volume by depressing the ribcage, and the interchondral part elevates the ribs.

Innervation:
Intercostal nerves (T1-T11)

Blood supply:
Anterior intercostal, posterior intercostal, internal thoracic and musculophrenic arteries; costocervical trunk

Question 8

Transversus thoracis

Answer 8

Attachments:
From the posterior surface of the inferior sternum to the internal surface of costal cartilages 2-6.

Actions:
Weakly depress the ribs.

Innervation:
Intercostal nerves (T2-T6).

Blood supply:
Sternal branches of internal thoracic artery

Question 9

Anterior scalene

Answer 9

Attachments:
Originates from the anterior tubercles of the transverse processes of C3-C6 and attaches onto the scalene tubercle (on the inner border of the first rib).

Function:
Elevation of the first rib. Ipsilateral contraction causes ipsilateral lateral flexion of the neck, and bilateral contraction causes anterior flexion of the neck.

Innervation:
Anterior rami of C5-C6.

Blood supply:
ascending cervical branch of the inferior thyroid artery.

Question 10

Middle scalene

Answer 10

Attachments:
Originates from the posterior tubercles of the transverse processes of C2-C7 and attaches to the scalene tubercle of the first rib.

Function:
Elevation of the first rib. Ipsilateral contraction causes ipsilateral lateral flexion of the neck.

Innervation:
Anterior rami of C3-C8.

Blood supply:
ascending cervical branch of the inferior thyroid artery

Question 11

Posterior scalene

Answer 11

Attachments:
Originates from the posterior tubercles of the transverse processes of C5-C7 and attaches into the second rib.

Function:
Elevation of the second rib, and ipsilateral lateral flexion of the neck.

Innervation:
Anterior rami of C6-C8.

Blood supply:
ascending cervical branch of the inferior thyroid artery; superficial cervical artery