Part III: Muscles of Ventilation
Reference & Reading: Egan's p.158-163

Primary Muscles
 Diaphragm
 Intercostal muscles

Accessory Muscles




Scalenes
Sternocleomastoid
Pectoralis Major
Abdominals
Rises from costal
margin

Connects at central
tendon


Hemidiaphragms
Separates thorax from
abdomen


Resting Position
When muscle contracts, drops floor of thoracic
cavity down


Pulls air in
Located between each
rib pair


External Intercostals

Internal Intercostals

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 www.gettyimages.com

Also called intercostal retractions
There is increased amount of negative pressure
generated

Clinical sign of increased WOB; look at suprasternal
notch


Retractions on infant
Collection of chest wall muscles
 Help to increase thoracic space, by assisting
the primary muscles:
Includes:





Scalene
Sternocleomastoid
Pectoralis
Trapezius

3 muscles
 Anterior
 Medial
 Posterior
Arise from lower 5 cervical
vertebrae & connect to 2nd rib
anteriorly
 Function:

 Normal
 With increased WOB
Rise from manubrium &
medial end of clavicle
 Insert into the skull


Function:
 Primary: supports head
 Increased WOB: raises sternum up
& out
Rises from clavicle &
anterior surface of
sternum


Function:
 Primary: hugging motion
 With increased WOB: pulls
opposite of primary function
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
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
External Oblique: arise
from lower 8 ribs

Internal Oblique: Arise
from iliac crest& inguinal
ligament


Fibrous aponeurosis

Arises from:
 costal cartilages
 Iliac crest
 Part of inguinal ligament
Connects to a
aponeurosis


Arises from pubic bones
Inserts into costal
cartilages 5 -7

Contraction ↓ distance
from xiphoid to pubis
