Three sheets of muscle in each of the spaces between ribs, whose fibres in the outer and middle layers cross at right angles
Intercostal muscles — external, internal and innermost.
Anatomy · Muscles
Intercostal muscles
Three layers between the ribs
Thorax · chest wall, move the ribs in breathing
The muscles that fill the eleven spaces between the twelve pairs of ribs. There are three layers, external, internal and innermost, and their fibres cross each other at right angles. They hold the chest wall firm against the pressure changes of breathing and help to lift and lower the ribs, and the nerves and vessels of the chest wall run between the inner two layers.
How to spot them
- ▸Three sheets between adjacent ribs; the external layer's fibres run down and forwards, the internal layer's down and backwards
- ▸Each space is supplied by an intercostal nerve, artery and vein running in the costal groove under the upper rib
- ▸In neurovascular order from above: vein, artery, nerve (VAN)
- ▸They are the meat between the bones of a rack of ribs
What to know
The outer layer's fibres run downwards and forwards, and its contraction lifts the ribs on breathing in
External intercostals — elevation of the ribs in inspiration.
A vein, an artery and a nerve run in a groove under the lower border of each upper rib, between the inner two layers
Intercostal muscles — the neurovascular bundle lies between the internal and innermost layers (VAN).
A chest drain is inserted just above the upper border of a rib to avoid a bundle running beneath the rib above
Intercostal muscles — the bundle lies in the costal groove on the lower border of the upper rib.
Supplied by the ventral rami of the first eleven thoracic nerves, which are also the source of the skin of the chest wall
Intercostal muscles — the intercostal nerves, T1 to T11.
The meat that a butcher leaves between the bones of a rack of pork or beef ribs
Intercostal muscles — the meat between the bones of spare ribs.
Their fibres, thin and taut, keep the spaces between the ribs from being sucked in during inspiration or blown out on coughing
Intercostal muscles — they resist pressure changes across the chest wall.
Key ideas
- The external layer lifts the ribs (a bucket-handle and pump-handle movement) and so widens the chest, while the internal layer lowers them in forced expiration; in quiet breathing the diaphragm does most of the work and the muscles mainly stiffen the wall.
- The neurovascular bundle sits on the lower border of each rib, sheltered by the costal groove, so needles and drains go in along the top of the rib below.
Quick-fire facts
- •There are eleven intercostal spaces on each side, each with three layers of muscle: external, internal and innermost intercostals
- •External intercostals: fibres run down and forwards; they run from the lower border of a rib to the upper border of the rib below, replaced near the sternum by the external intercostal membrane
- •Internal intercostals: fibres run down and backwards, at right angles to the external layer; from the costal groove to the upper border of the rib below
- •Innermost intercostals: the deepest layer, similar in direction to the internal layer, separated from it by the neurovascular bundle
- •Action: the external raise the ribs in inspiration; the internal and innermost lower them in forced expiration, and all stiffen the wall
- •Nerve supply: the intercostal nerves (T1 to T11)
- •Blood supply: anterior and posterior intercostal arteries
- •Order of the bundle in each space from superior to inferior: vein, artery, nerve (VAN)
- •A chest drain or aspiration needle is placed at the upper border of a rib to avoid the bundle
Drill it — 7 cards
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Sources
- TeachMeAnatomy — External intercostals
- TeachMeAnatomy — Internal intercostals