Respiratory Anatomy
Muscles of Expiration
• Unlike inspiration: expiration is an
interaction between passive & active forces
– active: rib cage and abdominal muscles
(opposition to diaphragm)
– passive: recoil forces, gravity
• 3 relatively independent forces:
– Passive forces
– Active diaphragm-abdomen forces
– Active rib cage forces
Internal Intercostals
• Fill spaces between ribs (except in back) on
the inside of the chest
• Connect ribs at opposite angles to external
intercostals
• Work in opposition to each other
(external/internal)
– Internal: pull down from the pelvis through
connection with abdominal muscles
– External: Pull upward from the spine, skull,
neck and fixate upper ribs
Transversus Thoracis
• Upward & outward from lower sternum to
insert into 2nd-6th ribs
• Flat muscle lying along inside front wall of
the chest
• Upper fibers run obliquely & assist in
pulling the chest downward
Subcostal Muscles
• Along lower inside back wall of the thorax
• Originate from lower ribs near the vertebral
attachment
• Run outward and up to insert into ribs one or
more higher
• Pull lower ribs (bucket handle) inward &
downward
Internal Rib Cage Muscles of Exhalation
Transversus
Thoracis
Outside view
of back wall
of lower six
ribs
Inside view
of front wall
of upper six
ribs
Subcostals
Internal
Intercostals
Serratus Posterior Inferior
• Slants upward & outward from lower
thoracic and upper lumbar vertebrae
• Inserts into the lowest four ribs
• Size, angle of pull & leverage to depress
the lower ribs with strong force
Quadratus Lumborum
• Strongly pulls down on the lowest floating
rib
• Pulls from its attachment along the upper
border of the hip (coxal bone)
• Flat vertical muscle in the posterior
abdominal wall
External Rib Cage Muscles of Exhalation
Serratus
Posterior
Inferior
Quadratus
Lumborum
Abdominal Muscles of Expiration
• Abdominal wall muscles provide major
active force in exhalation
• Contribution to breathing is compression of
viscera that push up on diaphragm
• Pushing displaces 60-80% of the exhaled
volume
• Function as rib cage depressors (pull down
on thorax) & abdominal compressors
Rectus Abdominus
• Large, vertical ribbon muscle
• Runs from front of pelvis along midline of
belly to the sternum & lower ribs
• Limited in amount of compression it applies
(Pulls in a straight line)
• Downward pull on sternum provides
powerful exhalatory force
External Oblique
• Originates from the lower 8 ribs and sweeps down
and forward
• Posterior fibers descend vertically to crest of coxal
bone
• Other fibers slant obliquely forward toward
midline
• Insert into tendinous sheath called abdominal
aponeurosis (covers rectus abdominus)
• Contribute to exhalation by pulling down on the
thorax while compressing viscera
Internal Obliques
• Thinner muscle, middle layer of abdominal wall
• Course of fibers opposite to external obliques
• Originate along upper border of coxal bone, fan
out and up
• Fan out at right angles to the external obliques
• Insert at the midline into the abdominal
aponeurosis & cartilages of the lower ribs
• External & Internal pull down on the thorax and
squeeze the viscera
Transversus Abdominus
• Deepest layer of abdominal muscle
• Horizontal fibers sweep from the vertebrae in the
back of the abdomen
• Insert into abdominal aponeurosis
• Attaches above to the lower border of the ribs (the
cartilages of the lower 6 ribs)
• Attaches below to the upper border of the pelvis
(coxal bone)- Like a corset (compress viscera)
• Corset action- Ext. & Int. obliques add
• Paired muscle- Tug of war
Abdominal Muscles of Exhalation
Rectus Abdominus
Transverse Abdominus
Internal
Oblique
External
Oblique
Passive forces
• Inspiration- raises rib cage against gravity
– cartilage are twisted
– viscera compressed
– alveolar sacs inflated against surface tension
– greater the inhalation= greater resistance
(muscles)
– Muscles relax= passive forces
• Untorquing
• Gravity
• Elastic recoil of lungs
Relaxation Pressure
Exhaled
Ribs
Raised
Torqued cartilage
Elastic Recoil
Inhaled
Gravity
Assignments
• Reading:
– Seikel: Ch.3 (Pgs. 99-109)
– Maue-Dickson: Ch.3 (116-122)