Muscles of Respiration

SHS 300

i-clicker

• Anatomy movies –A) integrate into lectures with questions –B) integrate into lectures with bonus questions –C) just show the damn movie so I can sleep

Muscles of Inspiration

•Diaphragm •Rib cage Elevators –External intercostals and internal intercostal (chondral portion) –Sternocleidomastoid –Levatores costarum or costal elevators –Scalenus group: Anterior, medius and posterior –Pectoralis major and minor –Subclavius –Serratus anterior and serratus posterior superior –Latissimus dorsi

1 Diaphragm ‘Fence in between’ •Thick sheet of muscle that forms floor of thorax –Separates abdomen and thorax •Dome or inverted bowl shape and slightly lower on left •In the center is the central tendon •Lateral muscles attach all around lower rib cage and circumference •Major inhalation muscle

Hoit & Hixon, 2005

Diaphragm

•Contraction pulls tendon downwards and forwards •Enlarges thorax vertically and circumerentially (elevates lower six ribs) •Increases pressure on abdominal contents

•Innervation: Phrenic nerve arising from cervical plexus

Diaphragm Origins and Insertions

•Origins: • Sternal part: Xiphoid process: posterior surface. •Costal part: Ribs 6 to 12 and their costal cartilages. •Insertion: Central tendon.

Hoit & Hixon, 2005

2 Diaphragm Origins and Insertions

Lumbar part: 1) Medial and lateral arcuate ligaments; 2) Vertebrae L1 - L3: bodies (via left and right crura). The left crus is a tendinous attachment of the diaphragm and is located on its posterior aspect. It passes to the left side of the aorta and blends with the anterior longitudinal ligament over the vertebrae and discs of L1 to L2.

The right crus is a tendinous attachment of the diaphragm located on its posterior aspect. It passes to the right side of the aorta and blends with the anterior longitudinal ligament over the vertebrae and discs of L1 to L3.

Diaphragm Apertures (Openings) •See SLP module for aperture anatomy •Aortic aperture: most inferoposterior opening located at the inferior border of T12 and slightly to the left of the mid line. •The margins of the aperture are defined by the crura laterally, the vertebral column posteriorly, and by the diaphragm itself anteriorly. •Allows the passage of the Descending aorta, Thoracic duct, Azygos and hemiazygos veins.

Hoit & Hixon, 2005

Diaphragm apertures

• Esophageal aperture: The oval shaped middle opening of the diaphragm located in the right crus, at the level of T10. •Muscle fibers from the crus surround the esophagus in a vertical tube •when the diaphragm moves during inspiration, the esophagus is constricted, preventing reflux of the gastric contents. •It allows the passage of the Esophagus, Esophageal vessels, Vagal trunks.

3 Vena Caval aperture •The square-shaped most superior opening •located in the anterior edge of the diaphragm (T8 and T9) •The vena cava adheres to the opening so as the diaphragm contracts in inspiration the aperture widens, stretching the vena cava to facilitate blood flow. •It allows the passage of the Inferior vena cava and right phrenic nerve.

Possible diaphragm actions

Hoit & Hixon, 2005

External Intercostals

•Major player in inhalation •Muscles that fill spaces between ribs •Runs FORWARDS and DOWNWARDS •Collectively forms a sheet of muscle that can work as a group

Hoit & Hixon, 2005

4 External Intercostal

•Contraction must affect position of upper rib or lower rib • Externals are anchored by first rib, cervical vertebrae and base of skull •Contraction elevates lower rib (either en masse or portions of ribs) •Contraction also stiffens spaces between ribs (prevents bulging or sucking inward during respiration)

Elevators •Sternocleidomastoid –Arises from sternum and clavicle to insert on mastoid process (2 slips) –Important in turning head, but muscle exerts force on sternum and clavicle when head is fixed – This force is transmitted to ribs and acts to elevate ribcage

Hoit & Hixon, 2005

Elevators

•Pectoralis major (pecs): large fan shaped on upper front rib cage (large chest muscle) –Originates from upper costal cartilages, sternum and inner clavicle –Inserts on humerus (upper arm bone) –When humerus is fixed, pectoralis major pulls sternum and ribs upward •Pectoralis minor: large, but thinner fan-shaped muscle below pectoralis major –Originates from ribs 2-5 (outer portion) and inserts on front of scapula – Elevates ribs 2-5

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