Musculature of Thoracic Wall

Question 1

Name the muscles (10) that attach to the thoracic cage and their innervation.

Answer 1

1. Pectoralis major
2. Pectoralis minor
3. Serratus anterior
4. Latissimus dorsi
5. Scalene’s
6. Intercostal muscles
7. Transverse thoracic muscles
8. Subcostal muscles
9. Levatores costarum
10. Serratus posterior sup. And inf.

Innervation: Ventral Rami Spinal Nerves

Question 2

Pectoralis Major

Answer 2

Origin:
1. Clavicle
2. Anterior sternum to the 6th rib
3. Originates off aponeurosis of obliquus externus abdominis

Insertion: Intertubercular groove of the humerus

Function:
Whole muscle:
1. ADduction, spinal rotation & elevation of the thorax (during inspiration)

2. Clavicular portion: internal rotation, flexion, and horizontal ADduction of the shoulder

Sternocostal portion: horizontal adduction and extension of the shoulder

Innervation: Medial and lateral pectoral nerves

Question 3

Pectoralis Minor

Answer 3

Origin: Ribs 3-5, Aponeurosis of intercostal muscles

Insertion: Coracoid process of scapula, medial border and superior surface

Function:
1. Scapular ABduction and protraction (bring forward)
2. Elevation of ribs in forced inspiration

Innervation: Medial and lateral pectoral nerves

Question 4

Serratus Anterior

Answer 4

Origin: Ribs 1-8, Aponeurosis of intercostal muscles

Insertion: Ventral (anterior) surface of scapula

Function:
Upward rotation of the scapula

Innervation: Long Thoracic nerve

Question 5

Scalene muscles (3)
1. Scalenus Anterior

Answer 5

Origin: Cervical transverse processes

Insertion: 1st rib

Function:
1. Flexion of cervical spine
2. Elevation of 1st rib during inspiration
3. Rotation of cervical spine to opposite side
4. Lateral bending of C-spine to the same side

Innervation: Ventral rami cervical nerves

Question 6

2. Scalenus Medius

Answer 6

Origin: Cervical transverse processes

Insertion: 1st rib

Function: Same as Scalenus Anterior

Innervation: Ventral rami cervical nerves

Question 7

Scalenus posterior

Answer 7

Origin: Cervical transverse processes

Insertion: 2nd rib

Innervation: Ventral rami cervical nerves

Function
1. Cervical flexion
2. Elevation of 2nd rib during inspiration
3. Lateral bending of C-spine to same side
4. Cervical rotation to opposite side

Question 8

What muscles sit in the intercostal space (3 groups)?
ALL innervated by ventral rami - intercostal nerves.

Answer 8

1. External intercostals
2. Internal intercostals
3. Innermost intercostals

Question 9

External Intercostals

• Fibers run inferior and anteriorly (inferomedially: hands in pockets)
• Inferiorly continuous with external abdominal oblique

Answer 9

Origin: Ribs 1-11 lower borders, Superior costotransverse ligaments

Insertion:
Ribs 2-12 upper borders, Sternum

Function:
1. Elevation of ribs in inspiration
2. Depression of the ribs in expiration
3. Rotation of thoracic spine to opposite side (unilateral)
4. Stabilization of rib cage

Innervation:
Ventral rami - intercostal nerves

Question 10

Internal Intercostals

• Deep to external intercostals m.
• Visible through external intercostals membrane
• Fibers run (superomedially: inferolaterally)
• Continues posteriorly as the Internal Intercostal

Answer 10

Origin: Ribs 1-11 inner surface, Costal cartilages, Sternum

Insertion: Ribs 2-12 upper border of inferior rib

Function: Same as External Intercostals

Innervation: Ventral rami - Intercostal nerves

Question 11

Innermost intercostal muscles

• Deep to internal intercostals
• Less well developed
• Runs in the same direction as internal intercostals (superomedially: inferolaterally)

Answer 11

Origin: Costal groove of rib above the rib of insertion

Insertion: Upper margin of the rib below the rib of origin

Function: Same as External Intercostals

Innervation: Ventral rami - Intercostal nerves

Question 12

Transverse Thoracis

Answer 12

Origin
- Sternum

• Ribs 3-6 (inner side)

Insertion: Ribs 2-5 (caudal borders)

Function:
1. Draws ribs downward (narrows chest)
2. Active in forced expiration

Innervation: Ventral rami - intercostal nerves

Question 13

Subcostal muscles

Answer 13

Origin: Lower ribs

Insertion: Inner surface of two or three ribs below rib of origin

Function: Draws adjacent ribs together

Innervation: Ventral rami - intercostal nerves

Question 14

Levatores Costarum

Answer 14

Origin: C7-T11 transverse processes

Insertion: Rib immediately below rib of origin

Function:
1. Elevation of ribs in inspiration
2. Lateral bending of spine

Innervation
Dorsal rami intercostal nerves