[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Anatomy](https://durgical.com/en/anatomy/) › [Chest](https://durgical.com/en/anatomy/region/chest/) › Internal intercostals [Muscular system](https://durgical.com/en/anatomy/system/muscular-system/) · [Chest](https://durgical.com/en/anatomy/region/chest/) # Internal intercostals The internal intercostals are the middle layer of muscles between the [ribs](https://durgical.com/en/anatomy/ribs/); they help pull the ribs down when breathing out hard, as in coughing. Official name: Internal intercostal muscles [See in 3D →](https://durgical.app/?from=durgipedia&lang=en#region=thorax&select=internal_intercostals&side=r) Opens in the Durgical app, no sign-up needed. ## What it is Muscles between the ribs, deeper, with fibres running down and back. ## What it does Help pull the ribs down when you breathe out forcefully (coughing, blowing). ## Key points - The intercostal neurovascular bundle runs deep to this muscle, between it and the innermost intercostals, sheltered in the costal groove of the rib above - From above down in the groove: vein, artery, nerve (VAN); the nerve is lowest and least protected - Needles and [chest](https://durgical.com/en/anatomy/region/chest/) drains go in just above the upper border of the rib below, to stay clear of the main bundle ## Key facts **Origin** Inferior border of rib above (floor of costal groove) **Insertion** Superior border of rib below; fibers run down and back; replaced behind by internal intercostal membrane **Action** Interosseous part depresses ribs in forced expiration; interchondral part elevates ribs (inspiration) **Nerve** Intercostal nerves (T1–T11) **Blood supply** Posterior and anterior intercostal arteries ## Relations **Superficial** [External intercostals](https://durgical.com/en/anatomy/external-intercostal-muscles/); in front, between the [costal cartilages](https://durgical.com/en/anatomy/costal-cartilage/), only the external intercostal membrane covers them **Deep** Intercostal neurovascular bundle ([intercostal veins](https://durgical.com/en/anatomy/right-posterior-intercostal-veins/), [posterior intercostal arteries](https://durgical.com/en/anatomy/posterior-intercostal-arteries/) and [intercostal nerves](https://durgical.com/en/anatomy/intercostal-nerves/)), then the [innermost intercostals](https://durgical.com/en/anatomy/innermost-intercostal-muscles/), endothoracic fascia and [pleura](https://durgical.com/en/anatomy/pleura/) **Medial** In front they reach the [sternum](https://durgical.com/en/anatomy/sternum/); behind, from the rib angles to the [spine](https://durgical.com/en/anatomy/region/spine/), they are replaced by the internal intercostal membrane ## How to find it Not palpable on its own. On ultrasound it is the middle of the three muscle layers between two rib shadows; the intercostal artery may be seen with colour Doppler, closer to mid-space in the back, near the spine. ## On imaging Ultrasound with a linear probe across a space shows the intercostal muscles between rib shadows, above the bright pleural line that slides with breathing; the neurovascular bundle lies under the upper rib. This view guides thoracentesis and drains over the lower rib. Contrast CT shows an intercostal artery bleeding after a drain or rib fracture. ## Clinical notes - Tube thoracostomy is usually placed in the triangle of safety (lateral border of the [pectoralis major](https://durgical.com/en/anatomy/pectoralis-major-muscle/), anterior border of the [latissimus dorsi](https://durgical.com/en/anatomy/latissimus-dorsi-muscle/) and a line at [nipple](https://durgical.com/en/anatomy/nipple/) level, about the 5th intercostal space), going over the top of the rib - Thoracentesis is usually done in the back or side of the chest, below the top of the effusion, again just above a rib - A collateral branch of the bundle runs along the upper border of the rib below, so even the safe zone is not risk free; in the back the vessels lie mid-space before entering the groove - Herpes zoster and post-thoracotomy pain follow the band of [skin](https://durgical.com/en/anatomy/skin/) supplied by one intercostal nerve ## Development Derived, with the external and innermost layers, from the thoracic myotomes; their segmental origin is the reason each space has its own nerve and vessels, and why intercostal pain and weakness follow single segments. ## Memory aid VAN from top to bottom in the costal groove: Vein, Artery, Nerve. ## Related conditions - [Costochondritis](https://durgical.com/en/conditions/costochondritis/) ## Test yourself Think of the answer, then tap the question to see it. ## Between which muscle layers does the intercostal neurovascular bundle run? Deep to the internal intercostals, between them and the innermost intercostals, sheltered in the costal groove of the rib above. ## What are the borders of the triangle of safety for tube thoracostomy? The lateral border of the pectoralis major, the anterior border of the latissimus dorsi and a line at nipple level (about the 5th intercostal space). ## What is the action of the interosseous and interchondral parts of the internal intercostal muscles? The interosseous part depresses the ribs in forced expiration; the interchondral part elevates the ribs in inspiration. ## Why is even the safe zone above the rib below not risk-free when inserting a chest drain? A collateral branch of the intercostal bundle runs along the upper border of the rib below; in the back the vessels also lie mid-space before entering the groove. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/anatomy/internal-intercostal-muscles/) Educational information, not medical advice. For any symptom, see a health professional. ## Its names **Official Latin (TA2)** musculi intercostales interni TA2 2312 **Official Spanish (DeCS)** Músculos intercostales internos DeCS D007366 **English (TA2)** Internal intercostal muscles ## Related - [Intercostal nerves](https://durgical.com/en/anatomy/intercostal-nerves/) - [Posterior intercostal arteries](https://durgical.com/en/anatomy/posterior-intercostal-arteries/) Sources: Terminologia Anatomica (TA2); [DeCS](https://decs.bvsalud.org/es/ths/resource/?id=22524&filter=ths_termall&q=M%C3%BAsculos%20Intercostales); [Anatomy, Thoracotomy and the Collateral Intercostal Neurovascular Bundle](https://www.ncbi.nlm.nih.gov/books/NBK544368/); [Anatomy, Thorax, Wall Movements](https://www.ncbi.nlm.nih.gov/books/NBK526023/); Anatomy of the Human Body (20th ed.): Development of the Muscles (Lea & Febiger (Gray's Anatomy, 1918), 1918) · adapted, Public domain. ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/anatomy/internal-intercostal-muscles/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anatomy/internal-intercostal-muscles/