Nn. Intercostalis

Nn. intercostales

are ventral branches of the thoracic spinal nerves; they are twelve pairs, but the lowest - the 12th nerve is called n. subcostalis. The 1st thoracic spinal nerve partly joins to plexus brachialis and the 12th - to plexus lumbalis.

Side branches of nn. intercostales

contain only sensory fibres: 1. r. cutaneus lateralis - spread near linea axillaris media to suppy the lateral thoracic and abdominal wall; 2. r. cutaneus anterior - emerge between the lateral margin of sternum and the lateral border of vagina musculi recti abdominis to supply the anterior thoracic and abdominal wall in the upper and middle regions.

Each intercostal nerve

enters the intercostal space between pars costalis pleurae parietalis and membrana intercostalis interna and runs forward between intercostal musles and m. transversus thoracis et m. subcostalis; the nerve is not covered by the rib, lies below corresponding intercostal vein and artery (v. et a. intercostalis posterior).

The lower six nerves

leave anterior parts of the intercostal spaces by passing deep to the costal cartilages to enter the anterior wall of the abdominal cavity. They run between m. transversus abdominis and m. obliquus internus abdominis to terminte at the margin of m. rectus abdominis.

The upper six intercostal nerves

run along the intercostal spaces to the margin of the sternum.

Nn. intercostales by sensory fibres

supply pars costalis pleurae parietalis, fascia endothoracica, fascia endoabdominalis, peritoneum parietale.

For female

the 2nd, the 3rd and the 4th rr. cutanei anteriores give off rr. mammarii mediales, but the 4th, 5th and 6th rr. cutanei laterales - rr. mammarii laterales to supply skin over glandula mammae.

Nn. intercostales are mixed nerves, by motor fibres

they supply the deep muscles of thorax (mm. intercostales externi et interni, m. transversus thoracis, mm. subcostales, mm. levatores costarum), the 3rd layer of superficial muscles of back (m. serratus posterior superior et inferior). The lower nerves supply the abdominal muscles (m. obliquus externus abdominis, m. obliquus internus abdominis, m. transversus abdominis, m. rectus abdominis, m. pyramidalis).