The intercostal nerves are part of the

somatic nervous system The somatic nervous system (SNS), or voluntary nervous system is the part of the peripheral nervous system associated with the voluntary control of body movements via skeletal muscles. The somatic nervous system consists of sensory nerves carry ...

, and arise from the anterior rami of the thoracic spinal nerves from T1 to T11. The intercostal nerves are distributed chiefly to the thoracic

pleura The pulmonary pleurae (''sing.'' pleura) are the two opposing layers of serous membrane overlying the lungs and the inside of the surrounding chest walls. The inner pleura, called the visceral pleura, covers the surface of each lung and dips ...

and abdominal

peritoneum The peritoneum is the serous membrane forming the lining of the abdominal cavity or coelom in amniotes and some invertebrates, such as annelids. It covers most of the intra-abdominal (or coelomic) organs, and is composed of a layer of mesot ...

, and differ from the anterior rami of the other

spinal nerves A spinal nerve is a mixed nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body. In the human body there are 31 pairs of spinal nerves, one on each side of the vertebral column. These are grouped into th ...

in that each pursues an independent course without plexus formation. The first two nerves supply fibers to the

upper limb The upper limbs or upper extremities are the forelimbs of an upright-postured tetrapod vertebrate, extending from the scapulae and clavicles down to and including the digits, including all the musculatures and ligaments involved with the shou ...

and thorax; the next four distribute to the walls of the

thorax The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the ...

; the lower five supply the walls of the thorax and

abdomen The abdomen (colloquially called the belly, tummy, midriff, tucky or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the front part of the abdominal segment of the tors ...

. The 7th intercostal nerve end at the xyphoid process of the

sternum The sternum or breastbone is a long flat bone located in the central part of the chest. It connects to the ribs via cartilage and forms the front of the rib cage, thus helping to protect the heart, lungs, and major blood vessels from injury. ...

. The 10th intercostal nerve terminates at the

navel The navel (clinically known as the umbilicus, commonly known as the belly button or tummy button) is a protruding, flat, or hollowed area on the abdomen at the attachment site of the umbilical cord. All placental mammals have a navel, altho ...

. The 12th ( subcostal) thoracic is distributed to the walls of the abdomen and

groin In human anatomy, the groin (the adjective is ''inguinal'', as in inguinal canal) is the junctional area (also known as the inguinal region) between the abdomen and the thigh on either side of the pubic bone. This is also known as the medial co ...

. Each of these fibers contains around 1300 axons. Unlike the nerves from the autonomic nervous system that innervate the visceral pleura of the thoracic cavity, the intercostal nerves arise from the

. This enables them to control the contraction of muscles, as well as provide specific sensory information regarding the skin and

parietal pleura The pulmonary pleurae (''sing.'' pleura) are the two opposing layers of serous membrane overlying the lungs and the inside of the surrounding chest walls. The inner pleura, called the visceral pleura, covers the surface of each lung and dips ...

. 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 The intercostal space (ICS) is the anatomic space between two ribs (Lat. costa). Since there are 12 ribs on each side, there are 11 intercostal spaces, each numbered for the rib superior to it. Structures in intercostal space * several kind ...

, 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.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.

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 In human anatomy, the internal thoracic artery (ITA), previously commonly known as the internal mammary artery (a name still common among surgeons), is an artery that supplies the anterior chest wall and the breasts. It is a paired artery, with one ...

and

transversus thoracis muscle The transversus thoracis muscle (), also known as triangularis sterni, lies internal to the thoracic cage, anteriorly. It is usually a thin plane of muscular and tendinous fibers, however on athletic individuals it can be a thick 'slab of meat' ...

, pierce the intercostales interni, the anterior intercostal membranes, and

pectoralis major The pectoralis major () is a thick, fan-shaped or triangular convergent muscle, situated at the chest of the human body. It makes up the bulk of the chest muscles and lies under the breast. Beneath the pectoralis major is the pectoralis minor, ...

, and supply the integument of the front of the thorax and over the mammary gland, forming the anterior cutaneous branches of the

; the branch from the second nerve unites with the anterior supraclavicular nerves of the

cervical plexus The cervical plexus is a plexus of the anterior rami of the first four cervical spinal nerves which arise from C1 to C4 cervical segment in the neck. They are located laterally to the transverse processes between prevertebral muscles from the me ...

. The fourth intercostal nerve is innervated by cutaneous slowly-adapting and rapidly-adapting

mechanoreceptor A mechanoreceptor, also called mechanoceptor, is a sensory receptor that responds to mechanical pressure or distortion. Mechanoreceptors are innervated by sensory neurons that convert mechanical pressure into electrical signals that, in animals, ...

s, especially by ones densely-packed under the areola; innervation subsequently triggers

oxytocin Oxytocin (Oxt or OT) is a peptide hormone and neuropeptide normally produced in the hypothalamus and released by the posterior pituitary. It plays a role in social bonding, reproduction, childbirth, and the period after childbirth. Oxytoci ...

release, which, when in the peripheral bloodstream, causes myoepithelial cell contraction and

lactation Lactation describes the secretion of milk from the mammary glands and the period of time that a mother lactates to feed her young. The process naturally occurs with all sexually mature female mammals, although it may predate mammals. The pr ...

: this is an example of a non-nerve-innervation muscular reflex.

Branches

Numerous slender muscular filaments supply the

Intercostales Intercostal muscles are many different groups of muscles that run between the ribs, and help form and move the chest wall. The intercostal muscles are mainly involved in the mechanical aspect of breathing by helping expand and shrink the size ...

, the

Subcostales The Subcostales (singular: subcostalis) (Infracostales) consist of muscular and aponeurotic fasciculi, which are usually well-developed only in the lower part of the thorax; each originates from the inner surface of one rib, and is inserted into t ...

, 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 The human areola (''areola mammae'', or ) is the pigmented area on the breast around the nipple. Areola, more generally, is a small circular area on the body with a different histology from the surrounding tissue, or other small circular ...

and the mamma; those of the fifth and sixth nerves supply the upper digitations of the

Obliquus externus abdominis The abdominal external oblique muscle (also external oblique muscle, or exterior oblique) is the largest and outermost of the three flat abdominal muscles of the lateral anterior abdomen. Structure The external oblique is situated on the lateral ...

. * The posterior branches run backward, and supply the skin over the

scapula The scapula (plural scapulae or scapulas), also known as the shoulder blade, is the bone that connects the humerus (upper arm bone) with the clavicle (collar bone). Like their connected bones, the scapulae are paired, with each scapula on eithe ...

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 Internal may refer to: * Internality as a concept in behavioural economics *Neijia, internal styles of Chinese martial arts *Neigong Neigong, also spelled ''nei kung'', ''neigung'', or ''nae gong'', refers to any of a set of Chinese breathing, ...

and the external oblique muscles, descends over the

iliac crest The crest of the ilium (or iliac crest) is the superior border of the wing of ilium and the superiolateral margin of the greater pelvis. Structure The iliac crest stretches posteriorly from the anterior superior iliac spine (ASIS) to the poste ...

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 The gluteal muscles, often called glutes are a group of three muscles which make up the gluteal region commonly known as the buttocks: the gluteus maximus, gluteus medius and gluteus minimus. The three muscles originate from the ilium and sac ...

, some of its filaments extending as low as the

greater trochanter The greater trochanter of the femur is a large, irregular, quadrilateral eminence and a part of the skeletal system. It is directed lateral and medially and slightly posterior. In the adult it is about 2–4 cm lower than the femoral head.Stan ...

of the

femur The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates wit ...

Additional images

File:Nervous system diagram-en.svg, Nervous system File:Gray530.png, Intercostal spaces, viewed from the left File:Brachial plexus.svg, Brachial plexus File:Brachial_plexus_color.svg, Brachial plexus with courses of spinal nerves shown

References

External links

* () * - "Abdominal Wall, Dissection, Lateral View" {{Authority control Spinal nerves