Name
Pronunciation
(in-ter-KOS-talz)
Origin/Proximal Attachment
Superior border of a lower rib (hint: runs opposite to external intercostals). Innermost ones often not well developed
Insertion/Distal Attachment
Inferior border of a rib above (each muscle fibre runs obliquely & inserts toward the costal cartilage
Action/Relevance
Internal: Depresses the ribs in expiration May elevate the ribs in forced inspiration Innermost: May assist in respiration
Innervation
Intercostal nerves
Notes
The internal intercostal muscles are the middle of the intercostal muscle groups within each intercostal space.
Within each space they arise from the inferior border of the rib that lies superiorly. The muscle fibres pass inferiorly and posteriorly to insert into the superior border of the rib that lies immediately inferiorly.
Each internal intercostal muscle is muscular from the angle of each respective rib posteriorly to the sternum anteriorly.
The internal intercostals are innervated by collateral branches of the first to eleventh intercostal nerves.