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 Outside view of back wall of lower six ribs Transversus Thoracis Inside view of front wall of upper six ribs Internal Intercostals Subcostals

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 Ribs Exhaled Raised Torqued cartilage Elastic Recoil Inhaled Gravity

Assignments Reading: Seikel: Ch.3 (Pgs. 99-109) Maue-Dickson: Ch.3 (116-122)