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| 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 | |
Theintercostal nerves are part of thesomatic nervous system, and arise from theanterior rami of thethoracic spinal nerves from T1 to T11.[1][2] The intercostal nerves are distributed chiefly to the thoracicpleura and abdominalperitoneum, and differ from the anterior rami of the otherspinal nerves in that each pursues an independent course without plexus formation.[1][3]
The first two nerves supply fibers to theupper limb and thorax; the next four distribute to the walls of thethorax; the lower five supply the walls of the thorax andabdomen.[3] The 7th intercostal nerve ends at thexyphoid process of thesternum.[3] The 10th intercostal nerve terminates at thenavel.[3] The 12th (subcostal) thoracic is distributed to the walls of the abdomen andgroin.[3] Each of these fibers contains around 1300 axons.[2]
Unlike the nerves from theautonomic nervous system that innervate the visceral pleura of the thoracic cavity, the intercostal nerves arise from thesomatic nervous system. This enables them to control the contraction of muscles, as well as provide specific sensory information regarding the skin andparietal 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 thevisceral pleura is experienced as an un-localizedache.
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 firstintercostal 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 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 theinternal mammary artery andtransversus thoracis muscle, pierce theintercostales interni, the anterior intercostal membranes, andpectoralis major, and supply the integument of the front of the thorax and over the mammary gland, forming the anterior cutaneous branches of thethorax; the branch from the second nerve unites with the anteriorsupraclavicular nerves of thecervical plexus.
Thefourth intercostal nerve is innervated by cutaneous slowly-adapting and rapidly-adaptingmechanoreceptors, especially by ones densely-packed under the areola; innervation subsequently triggersoxytocin release, which, when in the peripheral bloodstream, causesmyoepithelial cell contraction andlactation: this is an example of a non-nerve-innervation muscular reflex.
Numerous slender muscular filaments supply theIntercostales, theSubcostales, theLevatores costarum, theSerratus posterior superior, and theTransversus thoracis. At the front of the thorax some of these branches cross the costal cartilages from one intercostal space to another.
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 theintercostobrachial nerve.
The lateral cutaneous branch of the last thoracic nerve is large, and undivided.
It perforates theinternal and theexternal oblique muscles, descends over theiliac crest in front of the lateral cutaneous branch of theiliohypogastric nerve, and is distributed to the skin of the front part of thegluteal muscles, some of its filaments extending as low as thegreater trochanter of thefemur.
This article incorporates text in thepublic domain frompage 945 of the 20th edition ofGray's Anatomy(1918)
