Anatomy study note · Thorax

Intercostal muscles

Three thin layers of muscle filling each intercostal space: external, internal and innermost intercostals. They mainly keep the spaces rigid and move the ribs in forced breathing.

Key points

• External: fibres down and forward; internal: down and back.
• Innermost = transversus thoracis + innermost intercostal + subcostalis.
• Bundle between internal and innermost: VAN from above.
• Supplied by intercostal nerves.
• Main role: keep the spaces from bulging or sinking with pressure changes.
• Trunk muscles: from myotomes of the somites.
• Dorsal part → dorsal-ramus muscles; ventral part → ventral-ramus muscles.
• Skeletal muscle: multinucleated, peripheral nuclei, striated.
• Epimysium → perimysium → endomysium.

The full note in the atlas also covers

Relations · Features · Origin · Insertion · Action · Nerve supply · Histology · Development · Clinical notes

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Written from

• Snell’s Clinical Anatomy by Regions, 10th ed., ch. 4, PDF pp. 492–496, 509–510, 514–516
• Inderbir Singh’s Human Embryology, ch. 7, PDF pp. 108–109
• BRS Cell Biology & Histology, 7th ed., ch. 8, PDF pp. 135–144

More from the thorax

• Intercostal nerves
• Internal thoracic artery
• Internal thoracic vein
• Interventricular septum
• Joints of the ribs
• Left atrium
• Left coronary artery
• Left ventricle
• Levatores costarum
• Lung
• Lymph nodes of the thoracic wall
• Main and lobar bronchi

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