Name

# Internal Intercostal

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.