Thoracic muscles and their functions

Question 1

Thoracic muscles - general info

Answer 1

• Three groups autochtonous, heterochtonous and the diaphragm

Question 2

Autochtonous thoracic muscles

Answer 2

• Derived from the anterior parts of thoracic myotomes
• Preserve segmented organisation
• Includes:

1. External intercostal muscles
2. Internal intercostal muscles
3. Innermost intercostal muscles
4. Transversus thoracis muscle

• Innervated by the intercostal nerves
• Functionally classified as respiratory muscles

Question 3

Heterochtonous thoracic muscles

Answer 3

• Shifted to thorax secondarily during development of the upper extremities
• Includes:

1. Pectoralis major m.
2. Pectoralis minor m.
3. Subclavius m.
4. Serratus anterior m.

• Move upper extremity
• Innervated by the brachial plexus

Question 4

Pectoralis major muscle

Answer 4

• Trianglular - medial base and apex running towards axilla
• Origin:

1. Pars clavicularis - from medial 1/2 of the clavicle
2. Pars sternocostalis - from manubrium, sternal body and 2nd-7th costal cartilages
3. Pars abdominalis - anterior surface of rectus sheath

• Insertion: crista tuberculi majoris humeri
• Inferior fibres are attached more proximally
• Innervation: medial and lateral pectoral nerves rom the supraclavicular branch of the brachial plexus
• Function: adduction, pronation, arm flexion and during arm fixation: lifts thorax and is therefore an auxillary inspiratory muscle

Question 5

Pectoralis minor

Answer 5

• Below pectoralis major
• Origin: with 3 teeth on 3rd to 5th rib
• Runs craniolaterally to the shoulder
• Insertion: Coracoid process of the scapula
• Innervation: medial and lateral percotral nerves from the brachial plexus
• Function: pulls shoulder blade, and with it the entire brachail plexus, anterocaudally, at arm fixation: lifts thorax - auxillary inspiratory muscle

Question 6

Subclavius muscle

Answer 6

• Thin
• Below pectoralis major
• Origin: 1st rib
• Runs laterocranially
• Insertion: lateral part of the inferior face of the clavicle
• Innervation: subclavian nerve from the brachial plexus
• Function: Pulls clavice, and indirectly entire shoulder, down and forward, fixates shoulder to sternum, at fixed shoulder: lifts first rib - auxillary inspiratory muscle

Question 7

Serratus anterior muscle

Answer 7

• Flat muscle on the lateral side of the chest
• Origin: with 9 teeth from the cranial 9 ribs
• Runs dorsomedially
• Insertion: between wall of the thoracic cage and shoulder-blade to the medial margin and the inferior angle of the scapula
• Innervation: Long thoracic nerve from the brachail plexus
• Function: Pulls shoulder-blade from backbone, and inlines it towards the thorax, pulls the inferior angle of the scapula laterally and rotates scapula so that the glenoid cavits runs cranially and enables arm lifting about 90 degrees, wish shoulder blade fixated: pulls ribs cranially - auxillary inspiratory muscle

Question 8

External intercostal muscles

Answer 8

• Origin: Inferior edge of more cranially located rib (anterior margin of costal sulcus)
• Run in a mediocaudal direction
• Insertion: Superior margin of adjacent caudally lovated rib
• From tuberculum costae to the lateral margin of costal cartilage where they pass into the external intercostal membrane
• Innervation: intercostal nerves
• Function: Elavation of lower ribs, which enlarges the thoracic cavity - inspiratory muscle
• Forms external layer of intercostal muscles

Question 9

Internal intercostal muscles

Answer 9

• Origin: superior edge of caudal rib
• Run craniolaterally
• Insertion: inferior edge of cranially located rib
• Frontally reach up to sternum
• Dorsally reach up to level of angulus costae after which they proceed as the internal intercostal membrane
• Innervation: intercostal nerves
• Function: adduction of cranial ribs to caudal ribs and thereby diminishing the thoracic volume - expiratory muscle
• Forms middle layer of intercostal muscles

Question 10

Innermost intercostal muscles

Answer 10

• Origin: superior margin of cuadal rib
• Run craniolaterally
• Insertion: inferior edge of sulcus costae of more cranially located rib
• Innervation: intercostal nerves
• Function: Adduction of upper ribs to lower ribs, which narrows the slits and reduces the thoracic volume - expiratory muscles
• There is a slit between them and the internal intercostal muscles through which the intercostal nerves and vessels pass
• Forms internal layer of intercostal muscles

Question 11

Transversus thoracis muscle

Answer 11

• Origin: dorsal side of the xiphoid process and the adjacent part of the sternal body
• Diverges in a ray-shaped form craniolaterally
• Insertion: dorsal planes of 2nd to 6th ribs (costal cartilage)
• Innervation: Intercostal nerves
• Function: expiratory muscle