1. Unit 1: Gross Anatomy of the Chest
Part III: Muscles of Ventilation
Reference & Reading: Egan's p

2. Muscles of Ventilation
Primary Muscles
Diaphragm
Intercostal muscles
Accessory Muscles
Scalenes
Sternocleomastoid
Pectoralis Major
Abdominals

3. Diaphragm Rises from costal margin Connects at central tendon
Hemidiaphragms
Separates thorax from abdomen

4. Diaphragm - Function Resting Position
When muscle contracts, drops floor of thoracic cavity down
Pulls air in

5. Intercostal Muscles Located between each rib pair
External Intercostals
Internal Intercostals
External – rise from lower edge of each rib and into upper edge of rib below
Internal - lie beneath external intercostals; lower edge of rib form anterior end

6. Intercostal Muscles - Function
Active during quiet breathing
Elevates ribs, ↑ thoracic volume - occurs closer to exhalation
At increased lung volumes, ribs are lowered
Stabilizes chest wall during large pressure changes
Quiet Breathing – from

7. Retractions Also called intercostal retractions
There is increased amount of negative pressure generated
Clinical sign of increased WOB; look at suprasternal notch
Retractions on infant

8. Accessory Muscles - Inspiration
Collection of chest wall muscles
Help to increase thoracic space, by assisting the primary muscles:
Includes:
Scalene
Sternocleomastoid
Pectoralis
Trapezius

9. Scalene Muscles 3 muscles
Anterior
Medial
Posterior
Arise from lower 5 cervical vertebrae & connect to 2nd rib anteriorly
Function:
Normal
With increased WOB

10. Sternocledomastoids Rise from manubrium & medial end of clavicle
Insert into the skull
Function:
Primary: supports head
Increased WOB: raises sternum up & out

11. Pectoralis Muscles Rises from clavicle & anterior surface of sternum
Function:
Primary: hugging motion
With increased WOB: pulls opposite of primary function

12. Trapezius Muscles
Arise from the occipital bone in the skull & all thoracic vertebrae; insert into clavicle
Function:
Primary: shrug shoulders; raise or lower arms
Increased WOB: Raises rib cage

13. Accessory Muscles - Exhalation
Used to forcibly exhale (cough, sneeze, etc)
Muscles used are the abdominal muscles
Collectively compress abdominal contents to push diaphragm up
Includes:
External & internal obliques
Transverse abdominals
Rectus abdominus

14. Internal & External Oblique
External Oblique: arise from lower 8 ribs
Internal Oblique: Arise from iliac crest& inguinal ligament
Fibrous aponeurosis
Fibrous aponeurosis – fibrous sheath

15. Transverse Abdominis Arises from: Connects to a aponeurosis
costal cartilages
Iliac crest
Part of inguinal ligament
Connects to a aponeurosis

16. Rectus Abdominis Arises from pubic bones
Inserts into costal cartilages 5 -7
Contraction ↓ distance from xiphoid to pubis