Thoracic Wall - Muscles

Question 1

Describe quiet and forceful breathing

Answer 1

Quiet breathing in (quiet inspiration)
Diaphragm contracts and the dome moves inferiorly
External intercostal muscles raise the ribs

Forceful breathing in (exercise)
Diaphragm contracts and the dome moves inferiorly
External intercostal muscles raise the ribs
More muscles are active
Internal intercostal muscles (exhale)
Innermost intercostal muscles
(exhale)
Accessory muscles of respiration

Question 2

Describe the external intercostal muscles

Answer 2

Run in ‘hands in pockets’ direction (inferomedially)
Elevate the ribs during inspiration
Innervated by the intercostal nerves (of the corresponding intercostal space)

Question 3

Describe the internal intercostal muscles

Answer 3

Run in perpendicular to external
intercostals (superomedially)
Depress the ribs during expiration
Innervated by the intercostal nerves (of the corresponding intercostal space)
lie deep to external I muscles

Question 4

Describe the innermost intercostal muscles:

Answer 4

Deepest muscle layer
Depress the ribs during expiration helping to decrease the volume
Innervated by the intercostal nerves
Only visible posteriorly
Separated from the internal intercostals by the neurovascular bundle
Runs obliquely and downward
primarily found in the lateral part of the thoracic wall

Question 5

Describe the sternocleidomastoid:

Answer 5

Attaches to the sternum, clavicle and mastoid process (on the skull)
Elevates the sternum and clavicle via the pump handle movement
Increases the anterior- posterior diameter of the chest
Nerve supply from cranial nerve XI, the spinal accessory nerve
Accessory respiration muscle

Question 6

Describe the scalene muscles:

Answer 6

Anterior, middle and posterior
Anterior and middle scalene muscles attach from cervical vertebrae to rib 1
Posterior muscle attaches to rib 2
They elavate ribs 1 + 2
Nerve supply from cervical spinal nerves

Question 7

Describe the Pectoralis major:

Answer 7

Attaches from the medial clavicle & sternum and costal cartilages (1-6)
Fibres combine and attach in the intertubercular groove of humerus
Two heads act together to adduct and medially rotate
Clavicular head acts to flex
Nerve supply from medial and lateral pectoral nerves
Accessory muscle of respiration

Question 8

Describe the Pectoralis minor:

Answer 8

Attaches from the coracoid process of scapula
Fibres attach to ribs 3, 4 & 5
Draws the scapula towards the thoracic wall (protraction) and stabilizes
Nerve supply from medial pectoral nerve
Accessory muscle of respiration

Question 9

Describe the Serratus anterior:

Answer 9

Attaches from the upper 8 ribs
Fibres attach to medial border and inferior angle of scapula
Draws the scapula forward around the thoracic wall
If scapula is fixed, elevates ribs
Nerve supply by the long thoracic nerve

Question 10

Describe the abdominal muscles as accessory muscles of respiration:

Answer 10

Role in forced expiration
Contract to push the diaphragm upward, decreasing thoracic volume, and expelling air from the lungs
Essential in coughing and clearing the airway
Innervated by continuations of the intercostal nerves

Question 11

Describe the arterial supply to the thoracic:

Answer 11

Internal thoracic arteries branch from the subclavian artery
Lie lateral to the sternum and deep to the costal cartilages
Each give 6 branches anteriorly
Terminates into two arteries:

Musculophrenic artery (7-9 anterior intercostal arteries)
Superior epigastric artery
(continues to supply anterior abdominal wall)

Posterior intercostal arteries come direct from the thoracic aorta
Anastomoses with the anterior intercostal arteries laterally

Question 12

Describe venous drainage in the thoracic:

Answer 12

Follows the arteries
Anterior intercostal veins drain to the internal thoracic veins
Posterior intercostal veins drain to the azygous system of veins

Question 13

Describe the nervous innervation to the thoracic:

Answer 13

Nerve supply to the intercostal
muscles is via the intercostal
nerves
These are the ventral rami of the thoracic nerves
T1-T11: intercostal nerves
T12: sub costal nerves

Question 14

Describe briefly a spinal nerve and the 2 types

Answer 14

Ventral/ dorsal root ->
Spinal nerve -> Ventral ramus, dorsal ramus

Dorsal rami - motor innervation to intrinsic muscle of the back
Ventral rami - individual spinal nerves

Question 15

Describe the thoracic spinal nerves:

Answer 15

Ventral rami T1-12
Motor - intercostal and abdominal muscles
Sensory - Supply a strip of skin
* The area supplied by a single spinal
nerve is called a dermatome
* Intercostal nerves also supply the
parietal pleura and peritoneum

Question 16

What are the divisions of the innermost intercostal muscles ?

Answer 16

True - same direction and action as internal but only found laterally
Transversus thoracis - anterior
Subcostal - posterior