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Intercostal nerves
Intercostal nerves
	Diagram of the course and branches of a typical intercostal nerve.
	Intercostal nerves, the superficial muscles having been removed.
Details
From	Thoracic nerves (T1-T11)
Innervates	Intercostal muscle
Identifiers
Latin	nervi intercostales
MeSH	D007367
TA98	A14.2.04.006
TA2	6471
FMA	75467
	Anatomical terms of neuroanatomy [edit on Wikidata]

The intercostal nerves are part of the somatic nervous system, and arise from the anterior rami of the thoracic spinal nerves from T1 to T11.^[1]^[2] The intercostal nerves are distributed chiefly to the thoracic pleura and abdominal peritoneum, and differ from the anterior rami of the other spinal nerves in that each pursues an independent course without plexus formation.^[1]^[3]

The first two nerves supply fibers to the upper limb and thorax; the next four distribute to the walls of the thorax; the lower five supply the walls of the thorax and abdomen.^[3] The 7th intercostal nerve ends at the xyphoid process of the sternum.^[3] The 10th intercostal nerve terminates at the navel.^[3] The 12th (subcostal) thoracic is distributed to the walls of the abdomen and groin.^[3] Each of these fibers contains around 1300 axons.^[2]

Unlike the nerves from the autonomic nervous system that innervate the visceral pleura of the thoracic cavity, the intercostal nerves arise from the somatic nervous system. This enables them to control the contraction of muscles, as well as provide specific sensory information regarding the skin and parietal pleura. This explains why damage to the internal wall of the thoracic cavity can be felt as a sharp pain localized in the injured region. Damage to the visceral pleura is experienced as an un-localized ache.

The 1st thoracic nerve

The anterior division of the first thoracic nerve divides into two branches. The larger branch leaves the thorax in front of the neck of the first rib, and enters the brachial plexus. The smaller branch, the first intercostal nerve, runs along the first intercostal space, and ends on the front of the chest as the first anterior cutaneous branch of the thorax. Occasionally, this anterior cutaneous branch is missing.

The first intercostal nerve rarely gives off a lateral cutaneous branch; but sometimes sends a small branch to communicate with the intercostobrachial.

From the second thoracic nerve it frequently receives a connecting twig, which ascends over the neck of the second rib. This nerve was first described by Kuntz in 1927. There is considerable anatomic variation, but Kuntz nerve may be present in 40-80% of the population.^[4]^[5]

The upper thoracic nerves: 2nd–6th

The anterior divisions of the second, third, fourth, fifth, and sixth thoracic nerves, and the small branch from the first thoracic, are confined to the walls of the thorax, and are named thoracic intercostal nerves.

They pass forward in the intercostal spaces below the intercostal vessels. At the back of the chest they lie between the pleura and the posterior intercostal membranes, but soon they run between the internal intercostals and the innermost intercostals then anteriorly they lie between the pleura and the internal intercostals.

Near the sternum, they cross in front of the internal mammary artery and transversus thoracis muscle, pierce the intercostales interni, the anterior intercostal membranes, and pectoralis major, and supply the integument of the front of the thorax and over the mammary gland, forming the anterior cutaneous branches of the thorax; the branch from the second nerve unites with the anterior supraclavicular nerves of the cervical plexus.

The fourth intercostal nerve is innervated by cutaneous slowly-adapting and rapidly-adapting mechanoreceptors, especially by ones densely-packed under the areola; innervation subsequently triggers oxytocin release, which, when in the peripheral bloodstream, causes myoepithelial cell contraction and lactation: this is an example of a non-nerve-innervation muscular reflex.

Branches

Numerous slender muscular filaments supply the Intercostales, the Subcostales, the Levatores costarum, the Serratus posterior superior, and the Transversus thoracis. At the front of the thorax some of these branches cross the costal cartilages from one intercostal space to another.

Lateral cutaneous branches (rami cutanei laterales) are derived from the intercostal nerves, about midway between the vertebræ and sternum; they pierce the Intercostales externi and Serratus anterior, and divide into anterior and posterior branches.
The anterior branches run forward to the side and the forepart of the chest and skin, fourth nerve anterior branches supplying the areola and the mamma; those of the fifth and sixth nerves supply the upper digitations of the Obliquus externus abdominis.
The posterior branches run backward, and supply the skin over the scapula and Latissimus dorsi.

The lateral cutaneous branch of the second intercostal nerve does not divide, like the others, into an anterior and a posterior branch; it is named the intercostobrachial nerve.

The lower thoracic nerves: 7th–11th

The lower thoracic nerves: 12th

Anterior division

Lateral cutaneous branch

The lateral cutaneous branch of the last thoracic nerve is large, and undivided.

It perforates the internal and the external oblique muscles, descends over the iliac crest in front of the lateral cutaneous branch of the iliohypogastric nerve, and is distributed to the skin of the front part of the gluteal muscles, some of its filaments extending as low as the greater trochanter of the femur.

Additional images

Nervous system
Intercostal spaces, viewed from the left
Brachial plexus
Brachial plexus with courses of spinal nerves shown

References

This article incorporates text in the public domain from page 945 of the 20th edition of Gray's Anatomy (1918)

^ ^a ^b Ostrowska, Monika; de Carvalho, Mamede (2015-01-01), Tubbs, R. Shane; Rizk, Elias; Shoja, Mohammadali M.; Loukas, Marios (eds.), "Chapter 34 - Injuries of the Nerves of the Thorax", Nerves and Nerve Injuries, San Diego: Academic Press, pp. 525–543, doi:10.1016/b978-0-12-802653-3.00083-x, ISBN 978-0-12-802653-3, retrieved 2020-11-17
^ ^a ^b Hébert-Blouin, Marie-Noëlle; Spinner, Robert J.; Bishop, Allen T.; Shin, Alexander Y. (2012-01-01), Chung, Kevin C.; Yang, Lynda J. -S.; McGillicuddy, John E. (eds.), "CHAPTER 19 - Reconstructive procedures for the upper extremity", Practical Management of Pediatric and Adult Brachial Plexus Palsies, Philadelphia: W.B. Saunders, pp. 249–270, doi:10.1016/b978-1-4377-0575-1.00019-8, ISBN 978-1-4377-0575-1, retrieved 2020-11-17
^ ^a ^b ^c ^d ^e Narchi, Patrick; Singelyn, François; Paqueron, Xavier; Nicholls, Barry (2014-01-01), Benzon, Honorio T.; Rathmell, James P.; Wu, Christopher L.; Turk, Dennis C. (eds.), "55 - Truncal Blocks", Practical Management of Pain (Fifth Edition), Philadelphia: Mosby, pp. 745–754.e2, doi:10.1016/b978-0-323-08340-9.00055-4, ISBN 978-0-323-08340-9, retrieved 2020-11-17
^ Ramsaroop L, Partab P, Singh B, Satyapal KS. Thoracic origin of a sympathetic supply to the upper limb: the 'nerve of Kuntz' revisited. J Anat. 2001;199:675Y682
^ Marhold F, Izay B, Zacherl J, Tschabitscher M, Neumayer C. Thoracoscopic and anatomic landmarks of Kuntz's nerve: implications for sympathetic surgery. Ann Thorac Surg. 2008;86:1653Y1658.

External links

thoraxlesson5 at The Anatomy Lesson by Wesley Norman (Georgetown University) (paravertebralregion)
Atlas image: abdo_wall53 at the University of Michigan Health System - "Abdominal Wall, Dissection, Lateral View"