Muscles of Thorax.docx

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Western University
Anatomy and Cell Biology
Anatomy and Cell Biology 3319
Kem Rogers

Muscles of Thorax, Back & Neck Thoracic Cage • Includes thoracic vertebrae posteriorly, ribs laterally & sternum & costal cartilage anteriorly • Protective cage for heart, lungs & other organs • Supports shoulder girdles and upper limps • Provides attachment points for many muscles of back, neck, chest & shoulders • Intercostal spaces are occupied by intercostal muscles – lift & depress throax during breathing Sternum (breastbone) • 3 sections: o Manubrium  Superior section  Clavicular notches: articulate with clavicles (collarbones) superolaterally  Articulates with 1 & 2 ribs o Body  Midportion  Formed by 4 separate bones that fuse after puberty  Sides are notched where it articulates with the costal cartilages of the 2 to 7 rib o Xiphoid process  Forms inferior end  Tongue-shaped process  Plate of hyaline cartilate in youth  Doesn’t fully ossify until age 40  Blows to the chest can push xiphoid process into underlying heart or liver • 3 anatomical landmarks o Jugular notch  Suprasternal notch  Central indentation in the superior border of the manubrium  Lies in the same horizontal plane as the disc between the 2 and 4 thoracic vertebrae o Sternal angle  Inferior to jugular notch  Horizontal ridge across anterior surface of the sternum where manubrium joins the body  Fibrocartilage joint – hinge allowing sternal body to swing anteriorly as we inhale  In line with the disc between 4 & 5 thoracic vertebrae  Anteriorly lies at the level of the 2 ribs o Xiphisternal joint  Where sternal body and xiphoid process fuse  Lies at the level of 9 thoracic vertebrae  Deep to this joint – heart lies on diaphragm Ribs • 12 pairs of ribs • All ribs attach to thoracic vertebrae and run anteroinferiorly to reach the front of the chest • True ribs – Vertebrosternal ribs: superior 7 pairs – attach to sternum by their costal cartilages • False ribs: inferior ribs 8-12, attach to sternum indirectly or not at all o Verbrochondral ribs: ribs 8-10 attach to sternum indirectly – as each joins the costal cartilage above it o Floating ribs - Vertebral ribs: ribs 11 & 12 –no anterior attachments, costal cartilage lie imbedded in muscles of lateral body wall • Ribs increase in length from pair 1-7 and then decrease in length from 8-12 • Inferior margin of the rib cage or costal margin – formed by costal cartilages of ribs 7-10 • Right and left costal margins diverge from the region of xiphisternal joint, where they form infrasternal angle • Typical rib is bowed flat bone • Shaft/Body: Bulk of a rib • Superior border is smooth • Inferior border is sharp & thin & has a costal groove o Intercostal nerves and vessels are located within costal groove • Each rib is wide at the superior end and tapes at inferior surface • Each rib also has o Head  Wedge-shaped  Articulates with vertebral body by two facets • One facet joins the body of thoracic vertebra of the same number • One facet joins the body of the vertebra immediately superior o Neck  Short, constricted region just lateral to the head o Tubercle  Knob-like  Lateral to neck on posterior surface  Articulates with transverse process of the thoracic vertebra of the same number • Lateral to tubercle at angle of the rib – shaft curves sharply anteriorly and extends to costal cartilage anteriorly • Costal cartilage provide secure but flexible attachments of ribs to sternum and contribute to elasticity of cage • First rib o Atypical o Flattened from superior to inferior o Very broad o Subclavian vessels, large artery and vein serving the upper limb run in a groove along its superior surface • Other exceptions to typical rib pattern: o Rib 1 and ribs 10-12 only articulate with one vertebral body o Ribs 11-12 don’t articulate with vertebral transverse process Muscles Muscle Description O – Origin & I – Action Nerve Insertion Su ppl y Muscles of Thorax External • 11 pairs lie b/w ribs O – inferior border of Pull ribs toward one Intercostal Intercostal rib above another to elevate rib nerves • Fibres run obliquely (down & I – superior border of cage forward) • In lower intercostal spaces, fibersrib below Aid in inspiration Synergists of diaphragm are continuous with external Pulls inferior rib up oblique muscles forming part of abdominal wall Internal • 11 pairs lie between ribs O – superior border of Draw ribs together and Intercostal Intercostal • Fibres run deep to and at right rib below depress rib cage nerves I – inferior border Aid in expiration Inner and angles to external intercostals (costal groove) of rib Antagonist to external innermost (run downward & posteriorly) above intercostals • Lower intercostal muscles are When shortened - brings continuous with fibres of internal oblique muscle of abdominal wall superior rib down Diaphragm • Broad muscle pierced by aorta (in O – inferior surface of Prime mover of inspiration Phrenic the tendons so no muscles rib cage & sternum, Flattens on contraction nerves contra
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